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1. Distribution of Burkholderia pseudomallei within a 300-cm deep soil profile: implications for environmental sampling

Author: Khemngeun Pongmala, Alain Pierret, Priscia Oliva, Anne Pando, Viengmon Davong, Sayaphet Rattanavong, Norbert Silvera, Manophab Luangraj, Laurie Boithias, Khampaseuth Xayyathip, Ludovic Menjot, Melina Macouin, Emma Rochelle-Newall, Henri Robain, Amphone Vongvixay, Andrew J. H. Simpson, David A. B. Dance, and Olivier Ribolzi
Subjects: Medicine, Science
Abstract: Abstract The environmental distribution of Burkholderia pseudomallei, the causative agent of melioidosis, remains poorly understood. B. pseudomallei is known to have the ability to occupy a variety of environmental niches, particularly in soil. This paper provides novel information about a putative association of soil biogeochemical heterogeneity and the vertical distribution of B. pseudomallei. We investigated (1) the distribution of B. pseudomallei along a 300-cm deep soil profile together with the variation of a range of soil physico-chemical properties; (2) whether correlations between the distribution of B. pseudomallei and soil physico-chemical properties exist and (3) when they exist, what such correlations indicate with regards to the environmental conditions conducive to the occurrence of B. pseudomallei in soils. Unexpectedly, the highest concentrations of B. pseudomallei were observed between 100 and 200 cm below the soil surface. Our results indicate that unravelling the environmental conditions favorable to B. pseudomallei entails considering many aspects of the actual complexity of soil. Important recommendations regarding environmental sampling for B. pseudomallei can be drawn from this work, in particular that collecting samples down to the water table is of foremost importance, as groundwater persistence appears to be a controlling factor of the occurrence of B. pseudomallei in soil.
Published: 2022
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2. From shifting cultivation to teak plantation: effect on overland flow and sediment yield in a montane tropical catchment

Author: Olivier Ribolzi, Olivier Evrard, Sylvain Huon, Anneke de Rouw, Norbert Silvera, Keo Oudone Latsachack, Bounsamai Soulileuth, Irène Lefèvre, Alain Pierret, Guillaume Lacombe, Oloth Sengtaheuanghoung, and Christian Valentin
Subjects: Medicine, Science
Abstract: Abstract Soil erosion supplies large quantities of sediments to rivers of Southeastern Asia. It reduces soil fertility of agro-ecosystems located on hillslopes, and it degrades, downstream, water resource quality and leads to the siltation of reservoirs. An increase in the surface area covered with commercial perennial monocultures such as teak plantations is currently observed at the expanse of traditional slash-and-burn cultivation systems in steep montane environments of these regions. The impacts of land-use change on the hydrological response and sediment yields have been investigated in a representative catchment of Laos monitored for 13 years. After the gradual conversion of rice-based shifting cultivation to teak plantation-based systems, overland flow contribution to stream flow increased from 16 to 31% and sediment yield raised from 98 to 609 Mg km−2. This result is explained by the higher kinetic energy of raindrops falling from the canopy, the virtual absence of understorey vegetation cover to dissipate drop energy and the formation of an impermeable surface crust accelerating the formation and concentration of overland flow. The 25-to-50% lower 137Cs activities measured in soils collected under mature teak plantations compared to soils under other land uses illustrate the severity of soil erosion processes occurring in teak plantations.
Published: 2017
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3. Can Organic Amendments Improve Soil Physical Characteristics and Increase Maize Performances in Contrasting Soil Water Regimes?

Author: Phimmasone Sisouvanh, Vidhaya Trelo-ges, Supat Isarangkool Na Ayutthaya, Alain Pierret, Naoise Nunan, Norbert Silvera, Khampaseuth Xayyathip, and Christian Hartmann
Subjects: compost, vermicompost, soil matric potential, porosity, pore size distribution, root, Agriculture (General), S1-972
Abstract: Organic amendments are believed to help increase the soil carbon storage and therefore improve soil quality, which may be important in the context of climate change. However, the added value of organic amendments for farmers must be clearly demonstrated in order to convince them of the utility of their use. The aims of this study were: (i) to investigate the impact on maize of compost and vermicompost combined with two levels (negligible and significant) of plant water stress; and (ii) to determine how the organic amendments affected the soil’s physical properties and maize productivity. Water stress levels were imposed by controlling the matric potential of soil columns in which cultivated soil characteristics was mimicked (10 cm topsoil with organic amendments, above a 50 cm subsoil without any inputs containing the majority of the roots). Plant and soil characteristics were monitored daily for 70 days. Our results show that the use of organic amendments is profitable for farmers as: (i) maize performances were increased in both moisture regimes; and (ii) the improvement was particularly striking in terms of yield. No additional benefits were measured when using vermicompost instead of compost. The data suggest that the improvement in plant characteristics did not result from increased water storage in the soils with organic amendments, but rather from better access to the water, resulting in faster root development in the macroporosity of the amended soils.
Published: 2021
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4. Hydrological Regime and Water Shortage as Drivers of the Seasonal Incidence of Diarrheal Diseases in a Tropical Montane Environment.

Author: Laurie Boithias, Marc Choisy, Noy Souliyaseng, Marine Jourdren, Fabrice Quet, Yves Buisson, Chanthamousone Thammahacksa, Norbert Silvera, Keooudone Latsachack, Oloth Sengtaheuanghoung, Alain Pierret, Emma Rochelle-Newall, Sylvia Becerra, and Olivier Ribolzi
Subjects: Arctic medicine. Tropical medicine, RC955-962, Public aspects of medicine, RA1-1270
Abstract: BACKGROUND:The global burden of diarrhea is a leading cause of morbidity and mortality worldwide. In montane areas of South-East Asia such as northern Laos, recent changes in land use have induced increased runoff, soil erosion and in-stream suspended sediment loads, and potential pathogen dissemination. To our knowledge, few studies have related diarrhea incidences to catchment scale hydrological factors such as river discharge, and loads of suspended sediment and of Fecal Indicator Bacteria (FIB) such as Escherichia coli, together with sociological factors such as hygiene practices. We hypothesized that climate factors combined with human behavior control diarrhea incidence, either because higher rainfall, leading to higher stream discharges, suspended sediment loads and FIB counts, are associated with higher numbers of reported diarrhea cases during the rainy season, or because water shortage leads to the use of less safe water sources during the dry season. Using E. coli as a FIB, the objectives of this study were thus (1) to characterize the epidemiological dynamics of diarrhea in Northern Laos, and (2) to identify which hydro-meteorological and sociological risk factors were associated with diarrhea epidemics. METHODS:Considering two unconnected river catchments of 22 and 7,448 km2, respectively, we conducted a retrospective time series analysis of meteorological variables (rainfall, air temperature), hydrological variables (discharge, suspended sediments, FIB counts, water temperature), and the number of diarrheal disease cases reported at 6 health centers located in the 5 southern districts of the Luang Prabang Province, Lao PDR. We also examined the socio-demographic factors potentially affecting vulnerability to the effect of the climate factors, such as drinking water sources, hygiene habits, and recreational water exposure. RESULTS:Using thus a mixed methods approach, we found E. coli to be present all year long (100-1,000 Most Probable Number or MPN 100 mL-1) indicating that fecal contamination is ubiquitous and constant. We found that populations switch their water supply from wells to surface water during drought periods, the latter of which appear to be at higher risk of bacterial contamination than municipal water fountains. We thus found that water shortage in the Luang Prabang area triggers diarrhea peaks during the dry and hot season and that rainfall and aquifer refill ends the epidemic during the wet season. The temporal trends of reported daily diarrhea cases were generally bimodal with hospital admissions peaking in February-March and later in May-July. Annual incidence rates were higher in more densely populated areas and mostly concerned the 0-4 age group and male patients. CONCLUSIONS:We found that anthropogenic drivers, such as hygiene practices, were at least as important as environmental drivers in determining the seasonal pattern of a diarrhea epidemic. For diarrheal disease risk monitoring, discharge or groundwater level can be considered as relevant proxies. These variables should be monitored in the framework of an early warning system provided that a tradeoff is found between the size of the monitored catchment and the frequency of the measurement.
Published: 2016
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5. Diversity of soil biopores and their influence on soil water infiltration under various pedoclimatic conditions

Author: Charlotte Védère, Hanane Aroui Boukbida, Yvan Capowiez, Sougueh Cheik, Guillaume Coulouma, Rinh Pham Dinh, Séraphine Grellier, Claude Hammecker, Thierry Henry des Tureaux, Ajay Harit, Jean-Louis Janeau, Pascal Jouquet, Jean-Luc Maeght, Cornelia Rumpel, Stéphane Sammartino, Norbert Silvera, Siwaporn Siltecho, Lotfi Smaili, Bounsamay Soulileuth, and Nicolas Bottinelli
Abstract: Despite the large contribution of macropores made by soil engineers to the soil macroporosity and water infiltration, few studies have addressed the specific contribution of soil engineer groups, dynamics of biopores and their efficiency in conducting water. Thus, we aimed to investigate the link between soil macrofauna, soil biopores and water infiltration under different pedoclimatic conditions. To do so, we conducted an experimentation in twelve study sites with a large longitudinal gradient from France to Vietnam. The experiment consisted in the field incubation of repacked soil in cores (15 cm in height and 15 cm in diameter) and controlling the activity of soil engineers in the manner of litter bag. For each site, soil columns were: (i) covered with a mesh (200µm) or not and (ii) with or without addition of organic residues to the soil surface. After 12 months, we measured (i) the 3D organization of biopores by X-ray computed tomography and (ii) the saturated hydraulic conductivity by Beerkan method. In addition, soil macrofauna communities and the 3D organization of biopores was measured in each study field. Addition of organic residues increased up to 2-fold the volume percentage of biopores which reached similar values than those observed for each study field. The co-inertia analysis between the data matrix characterizing the shape of biopores and the data matrix of the macrofauna communities showed no statistically significant correlation. Saturated hydraulic conductivity increased with the presence of biopores by 2 to 50-fold with the lowest increased in soils presenting largest saturated hydraulic conductivity. In conclusion, these results demonstrated that biopores are rapidly regenerated regardless the pedoclimatic conditions while the efficiency of biopores in conducting water is related to soil properties.
Published: 2023
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6. Escherichia coli concentration, multiscale monitoring over the decade 2011–2021 in the Mekong River basin, Lao PDR

Author: Laurie Boithias, Olivier Ribolzi, Emma Rochelle-Newall, Chanthanousone Thammahacksa, Paty Nakhle, Bounsamay Soulileuth, Anne Pando-Bahuon, Keooudone Latsachack, Norbert Silvera, Phabvilay Sounyafong, Khampaseuth Xayyathip, Rosalie Zimmermann, Sayaphet Rattanavong, Priscia Oliva, Thomas Pommier, Olivier Evrard, Sylvain Huon, Jean Causse, Thierry Henry-des-Tureaux, Oloth Sengtaheuanghoung, Nivong Sipaseuth, and Alain Pierret
Subjects: General Earth and Planetary Sciences
Abstract: Bacterial pathogens in surface waters may threaten human health, especially in developing countries, where untreated surface water is often used for domestic needs. The objective of the long-term multiscale monitoring of Escherichia coli ([E. coli]) concentration in stream water, and that of associated variables (temperature (T), electrical conductance (EC), dissolved oxygen concentration ([DO]) and saturation (DO%), pH (pH), oxidation-reduction potential (ORP), turbidity (Turb), and total suspended sediment concentration ([TSS])), was to identify the drivers of bacterial dissemination across tropical catchments. This data description paper presents three datasets (see “Data availability” section) collected at 31 sampling stations located within the Mekong River and its tributaries in Lao PDR (0.6–25 946 km2) from 2011 to 2021. The 1602 records have been used to describe the hydrological processes driving in-stream E. coli concentration during flood events, to understand the land-use impact on bacterial dissemination on small and large catchment scales, to relate stream water quality and diarrhea outbreaks, and to build numerical models. The database may be further used, e.g., to interpret new variables measured in the monitored catchments, or to map the health risk posed by fecal pathogens.
Published: 2022
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7. In-stream Escherichia coli modeling using high-temporal-resolution data with deep learning and process-based models

Author: Ather Abbas, Sangsoo Baek, Norbert Silvera, Bounsamay Soulileuth, Yakov Pachepsky, Olivier Ribolzi, Laurie Boithias, and Kyung Hwa Cho
Abstract: Contamination of surface waters with microbiological pollutants is a major concern to public health. Although long-term and high-frequency Escherichia coli (E. coli) monitoring can help prevent diseases from fecal pathogenic microorganisms, such monitoring is time-consuming and expensive. Process-driven models are an alternative means for estimating concentrations of fecal pathogens. However, process-based modeling still has limitations in improving the model accuracy because of the complexity of relationships among hydrological and environmental variables. With the rise of data availability and computation power, the use of data-driven models is increasing. In this study, we simulated fate and transport of E. coli in a 0.6 km2 tropical headwater catchment located in the Lao People's Democratic Republic (Lao PDR) using a deep-learning model and a process-based model. The deep learning model was built using the long short-term memory (LSTM) methodology, whereas the process-based model was constructed using the Hydrological Simulation Program–FORTRAN (HSPF). First, we calibrated both models for surface as well as for subsurface flow. Then, we simulated the E. coli transport with 6 min time steps with both the HSPF and LSTM models. The LSTM provided accurate results for surface and subsurface flow with 0.51 and 0.64 of the Nash–Sutcliffe efficiency (NSE) values, respectively. In contrast, the NSE values yielded by the HSPF were −0.7 and 0.59 for surface and subsurface flow. The simulated E. coli concentrations from LSTM provided the NSE of 0.35, whereas the HSPF gave an unacceptable performance with an NSE value of −3.01 due to the limitations of HSPF in capturing the dynamics of E. coli with land-use change. The simulated E. coli concentration showed the rise and drop patterns corresponding to annual changes in land use. This study showcases the application of deep-learning-based models as an efficient alternative to process-based models for E. coli fate and transport simulation at the catchment scale.
Published: 2021
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8. Escherichia coli concentration, multiscale monitoring over the decade 2011–2021 in the Mekong basin, Lao PDR

Author: Laurie Boithias, Olivier Ribolzi, Emma Rochelle-Newall, Chanthanousone Thammahacksa, Paty Nakhle, Bounsamay Soulileuth, Anne Pando-Bahuon, Keooudone Latsachack, Norbert Silvera, Phabvilay Sounyafong, Khampaseuth Xayyathip, Rosalie Zimmermann, Sayaphet Rattanavong, Priscia Oliva, Thomas Pommier, Olivier Evrard, Sylvain Huon, Jean Causse, Thierry Henry-Des-Tureaux, Oloth Sengtaheuanghoung, Nivong Sipaseuth, and Alain Pierret
Abstract: Bacterial pathogens in surface waters may threaten human health, especially in developing countries, where untreated surface water is often used for domestic needs. The objective of the long-term multiscale monitoring of Escherichia coli concentration in stream water, and that of associated variables (temperature, electrical conductance, dissolved oxygen concentration and saturation, pH, oxidation-reduction potential, turbidity, and total suspended sediment concentration), was to identify the drivers of bacterial dissemination across tropical catchments. This data description paper presents three datasets (see section Data availability) collected at 31 sampling stations located within the Mekong river and its tributaries in Lao PDR (0.6–25,946 km2) from 2011 to 2021. The 1,602 records have been used to describe the hydrological processes driving in-stream Escherichia coli concentration during flood events, to understand land-use impact on bacterial dissemination on small and large catchment scales, to relate stream water quality and diarrhea outbreaks, and to build numerical models. The database may be further used e.g. to interpret new variables measured in the monitored catchments, or to map the health risk posed by fecal pathogens.
Published: 2022

9. Overland flow during a storm event strongly affects stream water chemistry and bacterial community structure

Author: Huong T. Le, Thomas Pommier, Olivier Ribolzi, Bounsamay Soulileuth, Sylvain Huon, Norbert Silvera, Emma Rochelle-Newall, Laboratoire d'Ecologie Microbienne - UMR 5557 (LEM), Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Ecole Nationale Vétérinaire de Lyon (ENVL)-VetAgro Sup - Institut national d'enseignement supérieur et de recherche en alimentation, santé animale, sciences agronomiques et de l'environnement (VAS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Vietnam Academy of Science and Technology (VAST), Institut d'écologie et des sciences de l'environnement de Paris (iEES Paris ), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Geosciences Environment Toulouse, Centre National de la Recherche Scientifique (CNRS), Representation du Laos (IRD), Institute of Research for sustainable Development (IRD), ANR-13-AGRO-0007,TecItEasy,Effets conjugués de l'expansion des plantations d'arbres et du changement climatique sur le fonctionnement hydro-sédimentaire des bassins versants tropicaux de montagne: la diversité microbienne aquatique comme un proxy de la conversion d'usage des terres(2013), and Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)
Subjects: [SDV.EE]Life Sciences [q-bio]/Ecology, environment, 2. Zero hunger, 0303 health sciences, 010504 meteorology & atmospheric sciences, Ecology, Lao PDR (Laos), DOC, 15. Life on land, Aquatic Science, Southeast Asia, 01 natural sciences, 6. Clean water, 03 medical and health sciences, Sustainability, 13. Climate action, [SDE]Environmental Sciences, CDOM, Land degradation, Ecology, Evolution, Behavior and Systematics, 030304 developmental biology, 0105 earth and related environmental sciences, Water Science and Technology
Abstract: International audience; As flood events are expected to become more frequent due to climate change, investigating how overland flow exports terrestrial nutrients, carbon and living organisms into aquatic systems is essential for understanding both soil and stream ecosystem status. Here we assessed how dissolved organic carbon (DOC), total suspended sediments (TSS), and stream bacterial diversity responded to stream discharge and overland flow during stormflow in a tropical catchment. A higher humification index and a decreasing ratio of allochthonous to autochthonous DOC indicated that DOC from soils was exported to stream during the flood. The delta C-13 and delta N-15 of particulate matter was indicative of a source in the cultivated areas of the upper catchment and of subsurface soils (stream banks and gullies) in the downstream section. Bacterial richness of particle-attached (PA) and the free-living (FL) fractions increased with the flood progression in the upstream section. Moreover, the community structure of the PA fraction in the stream was more similar to that of overland flow than was the FL fraction. This suggests that the soil PA bacterial community was washed-out with overland flow during the flood recession. The relative contribution of sources and the composition of TSS, rather than hydrological regime, significantly drove the composition of bacterial community. In conclusion, our results emphasize that overland flow during a flood event strongly influences the structure of stream bacterial communities further underlining the biological connectivity between terrestrial runoff and stream flow.
Published: 2021
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10. Decay Rate of Escherichia coli in a Mountainous Tropical Headwater Wetland

Author: Paty Nakhle, Laurie Boithias, Anne Pando-Bahuon, Chanthamousone Thammahacksa, Nicolas Gallion, Phabvilay Sounyafong, Norbert Silvera, Keooudone Latsachack, Bounsamay Soulileuth, Emma J. Rochelle-Newall, Yoan Marcangeli, Alain Pierret, Olivier Ribolzi, Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Department of Agricultural Land Management [Vientiane] (DALaM), Ministry of Agriculture and Forestry of Laos, Institut d'écologie et des sciences de l'environnement de Paris (iEES Paris ), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Institut de Recherche pour le Développement (IRD), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), and Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)
Subjects: Lao PDR, survival rates, Water supply for domestic and industrial purposes, fecal indicator bacteria, [SDE]Environmental Sciences, Hydraulic engineering, mesocosms, Mekong basin, TC1-978, TD201-500, water purification
Abstract: Surface water contamination by pathogen bacteria remains a threat to public health in the rural areas of developing countries. Fecal indicator bacteria (FIB) like Escherichia coli (E. coli) are widely used to assess water contamination, but their behavior in tropical ecosystems is poorly documented. Our study focused on headwater wetlands which are likely to play a key role in stream water purification of fecal pollutants. Our main objectives were to: (i) evaluate decay rates (k) of the total, particle-attached and free-living E. coli; (ii) quantify the relative importance of solar radiation exposition and suspended particles deposition on k; and (iii) investigate E. coli survival in the deposited sediment. We installed and monitored 12 mesocosms, 4500 mL each, across the main headwater wetland of the Houay Pano catchment, northern Lao People’s Democratic Republic (Lao PDR), for 8 days. The four treatments with triplicates were: sediment deposition-light (DL); sediment deposition-dark (DD); sediment resuspension-light (RL); and sediment resuspension-dark (RD). Particle-attached bacteria predominated in all mesocosms (97 ± 6%). Decay rates ranged from 1.43 ± 0.15 to 1.17 ± 0.13 day−1 for DL and DD treatments, and from 0.50 ± 0.15 to −0.14 ± 0.37 day−1 for RL and RD treatments. Deposition processes accounted for an average of 92% of E. coli stock reduction, while solar radiation accounted for around 2% over the experiment duration. The sampling of E. coli by temporary resuspension of the deposited sediment showed k values close to zero, suggesting potential survival or even growth of bacteria in the sediment. The present findings may help parameterizing hydrological and water quality models in a tropical context.
Published: 2021
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11. The Multiscale <scp>TROPIcal CatchmentS</scp> critical zone observatory <scp>M‐TROPICS</scp> dataset <scp>II</scp> : Land use, hydrology and sediment production monitoring in Houay Pano, northern Lao <scp>PDR</scp>

Author: Chanthamousone Thammahacksa, Norbert Silvera, Sylvain Huon, Khambai Phanthavong, Guillaume Lestrelin, Henri Robain, Keooudone Latsachack, Andrew Noble, Vincent Chaplot, Alain Pierret, Xaysatith Souliyavongsa, Yann Le Troquer, Jean-Pierre Thiébaux, Phapvilay Sounyaphong, Laurie Boithias, Khampaseuth Xayyathip, Jean-Louis Janeau, Kongkeo Phachomphon, Jean Riotte, Stéphane Audry, Olga Vigiak, Yves Auda, Anneke de Rouw, Nivong Sipaseuth, Marion Viguier, Sengkeo Tasaketh, Olivier Ribolzi, Pierre Marchand, Alounsavath Chanhphengxay, Thierry Henry des Tureaux, Anne Pando-Bahuon, Saysongkham Sayavong, Bounsamay Soulileuth, Jean-Luc Maeght, Oloth Sengtaheuanghoung, Jean-Pierre Bricquet, Pierre Moreau, Emma Rochelle-Newall, and Christian Valentin
Subjects: 2. Zero hunger, Hydrology, geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, 0207 environmental engineering, Drainage basin, Sediment, Tropics, 02 engineering and technology, 15. Life on land, 01 natural sciences, 6. Clean water, Water level, Catchment hydrology, Hydrology (agriculture), 13. Climate action, Environmental science, Water quality, 020701 environmental engineering, Surface runoff, 0105 earth and related environmental sciences, Water Science and Technology
Abstract: Mountain regions of the humid tropics are characterized by steep slopes and heavy rains. These regions are thus prone to both high surface runoff and soil erosion. In Southeast Asia, uplands are also subject to rapid land-use change, predominantly as a result of increased population pressure and market forces. Since 1998, the Houay Pano site, located in northern Lao PDR (19.85°N 102.17°E) within the Mekong basin, aims at assessing the long-term impact of the conversion of traditional slash-and-burn cultivation systems to commercial perennial monocultures such as teak tree plantations, on the catchment hydrological response and sediment yield. The instrumented site monitors hydro-meteorological and soil loss parameters at both microplot (1 m2) and small catchment (0.6 km2) scales. The monitored catchment is part of the network of critical zone observatories named Multiscale TROPIcal CatchmentS (M-TROPICS). The data shared by M-TROPICS in Houay Pano are (1) rainfall, (2) air temperature, air relative humidity, wind speed, and global radiation, (3) catchment land use, (4) stream water level, suspended particulate matter, bed particulate matter and stones, (5) soil surface features, and (6) soil surface runoff and soil detachment. The dataset has already been used to interpret suspended particulate matter and bed particulate matter sources and dynamics, to assess the impact of land-use change on catchment hydrology, soil erosion, and sediment yields, to understand bacteria fate and weed seed transport across the catchment, and to build catchment-scale models focused on hydrology and water quality issues. The dataset may be further used to e.g. assess the role of headwater catchments in large tropical river basin hydrology, support the interpretation of new variables measured in the catchment (e.g. contaminants other than fecal bacteria), and assess the relative impacts of both climate and land-use change on the catchment.
Published: 2021
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12. Supplementary material to 'In-stream Escherichia Coli Modeling Using high-temporal-resolution data with deep learning and process-based models'

Author: Ather Abbas, Sangsoo Baek, Norbert Silvera, Bounsamay Soulileuth, Yakov Pachepsky, Olivier Ribolzi, Laurie Boithias, and Kyung Hwa Cho
Published: 2021
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13. In-stream Escherichia Coli Modeling Using high-temporal-resolution data with deep learning and process-based models

Author: Norbert Silvera, Bounsamay Soulileuth, Olivier Ribolzi, Yakov Pachepsky, Laurie Boithias, Kyung Hwa Cho, Sang-Soo Baek, Ather Abbas, Institut d'écologie et des sciences de l'environnement de Paris (iEES Paris ), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), and Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)
Subjects: Technology, HSPF, Headwater catchment, business.industry, Deep learning, Soil science, Contamination, medicine.disease_cause, Environmental technology. Sanitary engineering, Environmental sciences, [SDU]Sciences of the Universe [physics], Scientific method, Geography. Anthropology. Recreation, medicine, Environmental science, High temporal resolution, GE1-350, Artificial intelligence, Subsurface flow, business, Escherichia coli, TD1-1066
Abstract: Contamination of surface waters with microbiological pollutants is a major concern to public health. Although long-term and high-frequency Escherichia coli (E. coli) monitoring can help prevent diseases from fecal pathogenic microorganisms, such monitoring is time-consuming and expensive. Process-driven models are an alternative means for estimating concentrations of fecal pathogens. However, process-based modeling still has limitations in improving the model accuracy because of the complexity of relationships among hydrological and environmental variables. With the rise of data availability and computation power, the use of data-driven models is increasing. In this study, we simulated fate and transport of E. coli in a 0.6 km2 tropical headwater catchment located in the Lao People's Democratic Republic (Lao PDR) using a deep-learning model and a process-based model. The deep learning model was built using the long short-term memory (LSTM) methodology, whereas the process-based model was constructed using the Hydrological Simulation Program–FORTRAN (HSPF). First, we calibrated both models for surface as well as for subsurface flow. Then, we simulated the E. coli transport with 6 min time steps with both the HSPF and LSTM models. The LSTM provided accurate results for surface and subsurface flow with 0.51 and 0.64 of the Nash–Sutcliffe efficiency (NSE) values, respectively. In contrast, the NSE values yielded by the HSPF were −0.7 and 0.59 for surface and subsurface flow. The simulated E. coli concentrations from LSTM provided the NSE of 0.35, whereas the HSPF gave an unacceptable performance with an NSE value of −3.01 due to the limitations of HSPF in capturing the dynamics of E. coli with land-use change. The simulated E. coli concentration showed the rise and drop patterns corresponding to annual changes in land use. This study showcases the application of deep-learning-based models as an efficient alternative to process-based models for E. coli fate and transport simulation at the catchment scale.
Published: 2021
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14. Can Organic Amendments Improve Soil Physical Characteristics and Increase Maize Performances in Contrasting Soil Water Regimes?

Author: Supat Isarangkool Na Ayutthaya, Norbert Silvera, Vidhaya Trelo-ges, Christian Hartmann, Alain Pierret, Khampaseuth Xayyathip, Phimmasone Sisouvanh, Naoise Nunan, Faculty of Agriculture [Khon Kaen University], Khon Kaen University [Thailand] (KKU), Institut d'écologie et des sciences de l'environnement de Paris (iEES Paris ), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Swedish University of Agricultural Sciences (SLU), and Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)
Subjects: 0106 biological sciences, compost, vermicompost, porosity, [SDV.SA.AGRO]Life Sciences [q-bio]/Agricultural sciences/Agronomy, Plant Science, soil matric potential, engineering.material, 01 natural sciences, pore size distribution, distribution, pore size, lcsh:Agriculture (General), Subsoil, 2. Zero hunger, Topsoil, Compost, 04 agricultural and veterinary sciences, Soil carbon, 15. Life on land, root, lcsh:S1-972, Soil quality, 6. Clean water, Water potential, plant water stress, Agronomy, 13. Climate action, Soil water, 040103 agronomy & agriculture, engineering, 0401 agriculture, forestry, and fisheries, Environmental science, Agronomy and Crop Science, Vermicompost, 010606 plant biology & botany, Food Science
Abstract: Organic amendments are believed to help increase the soil carbon storage and therefore improve soil quality, which may be important in the context of climate change. However, the added value of organic amendments for farmers must be clearly demonstrated in order to convince them of the utility of their use. The aims of this study were: (i) to investigate the impact on maize of compost and vermicompost combined with two levels (negligible and significant) of plant water stress, and (ii) to determine how the organic amendments affected the soil’s physical properties and maize productivity. Water stress levels were imposed by controlling the matric potential of soil columns in which cultivated soil characteristics was mimicked (10 cm topsoil with organic amendments, above a 50 cm subsoil without any inputs containing the majority of the roots). Plant and soil characteristics were monitored daily for 70 days. Our results show that the use of organic amendments is profitable for farmers as: (i) maize performances were increased in both moisture regimes, and (ii) the improvement was particularly striking in terms of yield. No additional benefits were measured when using vermicompost instead of compost. The data suggest that the improvement in plant characteristics did not result from increased water storage in the soils with organic amendments, but rather from better access to the water, resulting in faster root development in the macroporosity of the amended soils.
Published: 2021
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15. Surface and sub-surface flow estimation at high temporal resolution using deep neural networks

Author: Norbert Silvera, Olivier Ribolzi, Minjeong Kim, Joong-Hyuk Min, Mayzonee Ligaray, Sang-Soo Baek, Kyung Hwa Cho, Ather Abbas, Laurie Boithias, Ulsan National Institute of Science and Technology (UNIST), Korea Atomic Energy Research Institute [Daejeon, south Korea] (KAERI), University of the Philippines Diliman (UP Diliman), Géosciences Environnement Toulouse (GET), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), Institut d'écologie et des sciences de l'environnement de Paris (iEES Paris ), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), and Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)
Subjects: Surface (mathematics), 010504 meteorology & atmospheric sciences, Flow (psychology), 0207 environmental engineering, Climate change, Soil science, 02 engineering and technology, 01 natural sciences, Water cycle, 020701 environmental engineering, Hydrological Simulated Program-FORTRAN, Spatial analysis, Sub-surface flow, 0105 earth and related environmental sciences, Water Science and Technology, business.industry, Deep learning, Surface runoff, 6. Clean water, 13. Climate action, [SDU]Sciences of the Universe [physics], Environmental science, High temporal resolution, Long short-term memory (LSTM), Artificial intelligence, business, Deep learning model
Abstract: Recent intensification in climate change have resulted in the rise of hydrological extreme events. This demands modeling of hydrological processes at high temporal resolution to better understand flow patterns in catchments. To model surface and sub-surface flows in a catchment we utilized a physically based model called Hydrological Simulated Program-FORTRAN and two deep learning-based models. One deep learning model consisted of only one long short-term memory (simple LSTM), whereas the other model simulated processes in each hydrological response unit (HRU) by defining one separate LSTM for each HRU (HRU-based LSTM). The models use environmental time-series data and two-dimensional spatial data to predict surface and sub-surface flows at 6-minute time step simultaneously. We tested our models in a tropical humid headwater catchment in northern Lao PDR and compared their performances. Our results showed that the simple LSTM model outperformed the other models on surface runoff prediction with the lowest MSE (7.4e - 5 m(3 )s(-1)), whereas HRU-based LSTM model better predicted patterns and slopes in sub-surface flow in comparison with the other models by having the smallest MSE value (3.2e - 4 m(3 )s(-1)). This study demonstrated the performance of a deep learning model when simulating hydrological cycle with high temporal resolution.
Published: 2020
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16. Application of deep recurrent neural networks for modeling surface and sub-surface flow at high temporal resolution

Author: Norbert Silvera, Sang-Soo Baek, Ather Abbas, Olivier Ribolzi, Laurie Boithias, Mayzonee Ligaray, Joong-Hyuk Min, Minjeong Kim, and Kyung Hwa Cho
Subjects: Surface (mathematics), Recurrent neural network, Flow (mathematics), High temporal resolution, Biological system, Geology
Abstract: Recent increase in climate change has resulted in rise of hydrologic extreme events, which demands better understanding of flow patterns in catchment. Modeling surface and sub-surface flow at high temporal resolution helps to understand catchment dynamics. In this study, we simulated surface and sub-surface flow in a Laotian catchment at 6-minute resolution. We used one physically based model called Hydrological Simulated Program-FORTRAN (HSPF) and developed two deep learning-based models. One deep learning model consisted of only one long short-term memory (LSTM), whereas the other model simulated processes in each hydrologic response unit (HRU) by defining one separate LSTM for each HRU. The models consider environmental data as well as changing landuse in catchment and predict surface and sub-surface flows. Our results show that simple LSTM model outperformed other models for surface runoff prediction, whereas the HRU-based LSTM model better predicted patterns and slopes in sub-surface flow in comparison with other models.
Published: 2020
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17. Understorey vegetation drives surface runoff and soil loss in teak plantation-based system of Northern Laos

Author: Olivier Ribolzi, Laurie Boithias, Bounsamai Soulileuth, Oloth Sengtaheuanghoung, Layheang Song, Alain Pierret, Phabvilay Sounyafong, Norbert Silvera, Chantha Oeurng, Anneke de Rouw, and Christian Valentin
Subjects: Hydrology, Soil loss, Environmental science, Understorey vegetation, Surface runoff
Abstract: Humid tropical mountainous area experiences serious soil erosion due to rapid changes in landuse, sometimes implying erosion prone management practices. In this study, we hypothesized that keeping understorey in teak tree plantation would protect soil and avoid soil erosion. We assessed the effects of 4 management practices in teak tree plantation area on water and soil losses using 6 replicated 1-m2 microplots in four plantations situated in Northern Laos during the wet season of 2017. The landuses in the four plantations were teak without understorey (TNU), teak with low density of understorey (TLU), teak with high density of understorey (THU), and teak with broom grass, Thysanolaena latifolia (TBG). During the wet season of 2017, we monitored surface runoff and soil loss for 22 rainfall events. We also measured some of the teak tree and understorey characteristics (i.e. height and percentage of cover) and the percentage areas of soil surface features (i.e. litter, free aggregates, crusting, etc.). Relationships among these variables was estimated through multiple statistics and regression analyses. We found that runoff coefficient and soil loss were the smallest for THU and TBG: runoff coefficient was 23% for both treatments, and soil losses were 465 and 381 g m-2, respectively. Runoff coefficient and soil loss for TLU were 35% and 1115 g m-2, respectively. We observed the highest runoff coefficient and soil loss under TNU (60%, 5455 g m-2) associated to the highest crusting rate (82%). High runoff coefficient and soil loss under TNU was explained by the kinetic energy of rain drops falling from the broad leaves of the tall teak trees down to bare soil, devoid of plant residues, thus leading to severe soil surface crusting and detachment. Overall, promoting understorey such as broom grass in teak tree plantations would (1) limit surface runoff and improve soil infiltrability, thus increase the soil water stock available for both root absorption and groundwater recharge, and (2) mitigate soil loss and favour soil fertility conservation.
Published: 2020
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18. Mise en œuvre des principes FAIR pour les données de recherche des surfaces continentales: enjeux, freins et bénéfices. Exemple du système d’information Theia/OZCAR

Author: Charly Coussot, Guillaume Brissebrat, Antony Mauclerc, Brice Boudevillain, Sylvie Galle, Jean-Christophe Desconnets, Genevieve Le Henaff, Hugues Alexandre, Isabelle Braud, Rémi Cailletaud, Marie-Françoise Gerard, Agnès Herrmann, Jean‐baptiste Paroissien, Hervé Squividant, Sylvain Grellet, Rémy Decoupes, Olivier Lobry, Juliette Fabre, Norbert Silvera, Gérard Cochonneau, Flora Branger, Philippe Baillion, Santiago Gabillard, Eric Lajeunesse, Olivier Laarman, Patrick Juen, Marie-Claire Pierret, Arnaud Dubreuil, Véronique Chaffard, Annick Battais, Riverly (Riverly), Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Institut des Géosciences de l’Environnement (IGE), Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement (IRD)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Université Grenoble Alpes (UGA), Laboratoire Ecologie Fonctionnelle et Environnement (ECOLAB), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut Ecologie et Environnement (INEE), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Centre d'études spatiales de la biosphère (CESBIO), Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Géosciences Rennes (GR), Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Central des Ponts et Chaussées (LCPC), Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA), Services communs OMP (UMS 831), Centre National de la Recherche Scientifique (CNRS), Géosciences Environnement Toulouse (GET), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), Laboratoire de l'Atmosphère et des Cyclones (LACy), Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Météo France, UMR 228 Espace-Dev, Espace pour le développement, Université de Guyane (UG)-Université des Antilles (UA)-Institut de Recherche pour le Développement (IRD)-Université de Perpignan Via Domitia (UPVD)-Avignon Université (AU)-Université de La Réunion (UR)-Université de Montpellier (UM), Laboratoire d'étude des Interactions Sol - Agrosystème - Hydrosystème (UMR LISAH), Institut de Recherche pour le Développement (IRD)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Écophysiologie des Plantes sous Stress environnementaux (LEPSE), Institut National de la Recherche Agronomique (INRA)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), Laboratoire d'Hydrologie et de Géochimie de Strasbourg (LHyGeS), Ecole et Observatoire des Sciences de la Terre (EOST), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Strasbourg (UNISTRA)-Centre National de la Recherche Scientifique (CNRS)-École Nationale du Génie de l'Eau et de l'Environnement de Strasbourg (ENGEES)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut de Physique du Globe de Paris (IPGP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), Sol Agro et hydrosystème Spatialisation (SAS), AGROCAMPUS OUEST, Orange Labs R&D [Rennes], France Télécom, Institut des Sciences de la Terre d'Orléans - UMR7327 (ISTO), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Biogéosystèmes Continentaux - UMR7327, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Bureau de Recherches Géologiques et Minières (BRGM) (BRGM)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut de Recherche pour le Développement (IRD), Institut d'écologie et des sciences de l'environnement de Paris (iEES Paris ), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), CNRS-INSU, RiverLy - Fonctionnement des hydrosystèmes (RiverLy), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP ), Laboratoire Ecologie Fonctionnelle et Environnement (LEFE), Institut Ecologie et Environnement (INEE), Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Météo-France, Institut de Recherche pour le Développement (IRD)-Université de Perpignan Via Domitia (UPVD)-Avignon Université (AU)-Université de La Réunion (UR)-Université de Montpellier (UM)-Université de Guyane (UG)-Université des Antilles (UA), Institut de Recherche pour le Développement (IRD)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro - Montpellier SupAgro, Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École Nationale du Génie de l'Eau et de l'Environnement de Strasbourg (ENGEES)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-INSTITUT AGRO Agrocampus Ouest, Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), ANR-19-DATA-0003,FairTOIS,Implémenter les principes FAIR dans le système d'information Theia/OZCAR(2019), Observatoire des Sciences de l'Univers de Grenoble (OSUG ), Institut national des sciences de l'Univers (INSU - CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université Grenoble Alpes (UGA)-Météo-France, Institut de Recherche pour le Développement (IRD) [NA], OZCAR-RI [NA], Centre National de la Recherche Scientifique (INSU) [NA]., Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées, Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2), Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Université de Rennes 2 (UR2), Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), and Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)
Subjects: FAIRisation des données, Computer science, Data management, 0208 environmental biotechnology, Interoperability, Portail de données, OZCAR-RI, 02 engineering and technology, World Wide Web, information system, data portal, Controlled vocabulary, Information system, Science de l’environnement, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Water Science and Technology, critical zone, FAIR data, business.industry, land surface, Data discovery, 020801 environmental engineering, Metadata, in situ observations, Data model, [SDU]Sciences of the Universe [physics], [SDE]Environmental Sciences, Faceted search, business
Abstract: International audience; La science ouverte vise à faciliter l’accès aux publications et aux données de la recherche. Elle a pour objectif d’accélérer les avancées scientifiques en encourageant les collaborations, la réutilisation des données et l’interdisciplinarité.Avoir une approche interdisciplinaire intégrée du Système Terre nécessite de pouvoir combiner des données hétérogènes de différents types, de différentes disciplines et provenant de différentes sources. Pour favoriser la réutilisation des données et l’interdisciplinarité, l’interopérabilité des données et des systèmes sont des enjeux cruciaux.L'infrastructure française de recherche sur la zone critique OZCAR-RI (1), regroupe 21 observatoires, dont deux situés en Afrique, qui échantillonnent sur le long terme différents compartiments de la Zone Critique (2). Ces observatoires ont historiquement développé leurs propres systèmes de gestion et de distribution des données. Cependant, ces efforts ont généralement été menés de manière indépendante. Cela a conduit à une situation très hétérogène en termes de description des données, de vocabulaire et d'interopérabilité, ce qui se traduit par un manque général de visibilité des données au sein et à l’extérieur de la communauté OZCAR-RI. Afin d'améliorer cette situation, le système d'information Theia/OZCAR a été construit en 2020 pour rendre FAIR (Findable, Accessible, Interoperable, Reusable) l’ensemble de ces données in-situ d’observation des surfaces continentales (3) avec un portail d’accès unique.Il a été nécessaire de proposer des solutions techniques pour collecter et décrire les données, afin de faciliter leur découverte et les rendre interopérables. Ces solutions s’appuient sur des standards d’échange, de description de données et de leur moyen d’acquisition, et sur la construction d’un vocabulaire contrôlé commun, le thésaurus de variable Theia/OZCAR. Si cela nécessite un travail important de normalisation pour bien décrire les données de la part des producteurs, les bénéfices attendus sont une diffusion plus large et une réutilisation accrue des données impliquant davantage de visibilité et de crédit pour les équipes qui les collectent et des opportunités de participation à des recherches interdisciplinaires et à de réseaux internationaux. D’autre part, la déclaration de licences libres protège les auteurs et favorise la réutilisation des données tout en garantissant les droits d’auteurs. De plus, si un DOI (Digital Object Identifer) est assigné au jeu de données ou si leur description fait l'objet d'un data paper, il est possible de suivre leur utilisation via la citation des DOI ou du data paper. Les étapes de construction du SI Theia/OZCAR ont permis de fédérer une communauté de gestionnaire et de producteurs de données autour des données de la zone critique. La montée en qualité des données nécessite des interactions fortes entre thématiciens et informaticiens.(1) https://www.ozcar-ri.org/fr/ozcar-observatoires-de-la-zone-critique-applications-et-recherche/(2) La Zone Critique désigne la pellicule la plus externe de la planète Terre, depuis lesroches non altérées jusqu’au sommet de la végétation, celle qui est le siège d’interactionschimiques entre l’air, l’eau et les roches et est le siège de la vie et l’habitat de l’espèce hu-maine(3) Braud, Isabelle, et al. ”Building the information system of the French Critical ZoneObservatories network: Theia/OZCAR-IS.” Hydrological Sciences Journal (2020): 1-19.10.1080/02626667.2020.1764568
Published: 2020
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19. Linking crop structure, throughfall, soil surface conditions, runoff and soil detachment: 10 land uses analyzed in Northern Laos

Author: Anneke de Rouw, Norbert Silvera, Christian Valentin, Olivier Ribolzi, Guillaume Lacombe, Alain Pierret, Phabvilay Sounyafong, Bounsamai Soulileuth, and Oloth Sengtaheuanghoung
Subjects: Environmental Engineering, 010504 meteorology & atmospheric sciences, Erosion control, F08 - Systèmes et modes de culture, Micro-plot experiment, Conservation des sols, 01 natural sciences, Soil crust, couverture du sol, Environmental Chemistry, Couverture végétale, Throughfall kinetic energy, Waste Management and Disposal, Multiple linear regression, 0105 earth and related environmental sciences, P36 - Érosion, conservation et récupération des sols, Hydrology, Utilisation des terres, Montane Southeast Asia, 04 agricultural and veterinary sciences, Plant litter, Throughfall, Pollution, Soil loss, Ruissellement, E11 - Économie et politique foncières, Soil water, 040103 agronomy & agriculture, Erosion, 0401 agriculture, forestry, and fisheries, Environmental science, Plant cover, Surface runoff
Abstract: In Montane Southeast Asia, deforestation and unsuitable combinations of crops and agricultural practices degrade soils at an unprecedented rate. Typically, smallholder farmers gain income from "available" land by replacing fallow or secondary forest by perennial crops. We aimed to understand how these practices increase or reduce soil erosion. Ten land uses were monitored in Northern Laos during the 2015 monsoon, using local farmers' fields. Experiments included plots of the conventional system(food crops and fallow), and land uses corresponding to new market opportunities (e.g. commercial tree plantations). Land uses were characterized by measuring plant cover and plant mean height per vegetation layer. Recorded meteorological variables included rainfall intensity, throughfall amount, throughfall kinetic energy (TKE), and raindrop size. Runoff coefficient, soil loss, and the percentage areas of soil surface types (free aggregates and gravel; crusts; macro-faunal, vegetal and pedestal features; plant litter) were derived from observations and measurements in 1-m(2) micro-plots. Relationships between these variables were explored with multiple regression analyses. Our results indicate that TKE induces soil crusting and soil loss. By reducing rainfall infiltration, crusted area enhances runoff, which removes and transports soil particles detached by splash over non-crusted areas. TKE is lower under land uses reducing the velocity of raindrops and/or preventing an increase in their size. Optimal vegetation structures combine minimum height of the lowest layer (to reduce drop velocity at ground level) and maximum coverage (to intercept the largest amount of rainfall), as exemplified by broom grass (Thysanolaena latifolia). In contrast, high canopies with large leaves will increase TKE by enlarging raindrops, as exemplified by teak trees (Tectona grandis), unless a protective understorey exists under the trees. Policies that ban the burning of multi-layered vegetation structure under tree plantations should be enforced. Shade-tolerant shrubs and grasses with potential economic return could be promoted as understorey.
Published: 2018
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20. Comparisons of xylem sap flux densities in immature hybrid rubber tree clones under varied environmental conditions

Author: Frédéric C. Do, Norbert Silvera, Poonpipope Kasemsap, S. Isarangkool Na Ayutthaya, Ratchanee Rattanawong, and S. Meetha
Subjects: Horticulture, Thermal dissipation, Natural rubber, Dry soil, visual_art, visual_art.visual_art_medium, Randomized block design, Flow density, Flux, Xylem, Biology, Hybrid
Abstract: The objective of this research was to evaluate the diversity of xylem sap flux density in four immature hybrid rubber clones, including the main mother clone RRIM600, planted in northeast Thailand. These hybrid clones, bred from the original RRIM600 (female) and RRII105 (male) clones, differed in trunk diameters. The age of the sample trees was 4 years. Measurements were taken from April to October 2016, within the full-leaves stage. The experimental design consisted of a randomized block design of hybrids and blocks for performing measurements at four environmental conditions: well-watered and sunny day (VPD 2.2 kPa), well-watered and extremely sunny day (VPD 3.2 kPa), well-watered and cloudy day (VPD 0.9 kPa) and dry soil and extremely sunny day (VPD 4.2 kPa). Sap flow density was recorded through the transient thermal dissipation method (10 min heating and 20 min cooling in a half hour period; TTD10) with a Granier's type probe. The results show that the maximum and daily sap flux densities were reduced by 40-45% on the cloudy day and soil drought conditions, compared to the well-watered and sunny day condition, while daily sap flux density in the extremely sunny day condition slightly increased. Differences in trunk size were insignificant in relation to the varying sap flux densities.
Published: 2018
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21. Quantifying the effect of overland flow on Escherichia coli pulses during floods: Use of a tracer-based approach in an erosion-prone tropical catchment

Author: Olivier Ribolzi, Cyril Zouiten, Laurie Boithias, Bounsamay Soulileuth, Guillaume Lacombe, Emma Rochelle-Newall, Olivier Evrard, Elodie Robert, Thomas Pommier, Chanthamousone Thammahacksa, Norbert Silvera, Keooudone Latsachack, Yves Auda, Marion Viguier, Sylvain Huon, Oloth Sengtaheuanghoung, Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Gestion de l'Eau, Acteurs, Usages (UMR G-EAU), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-AgroParisTech-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro - Montpellier SupAgro, Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), Département Environnements et Sociétés (Cirad-ES), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad), Institut de Recherche pour le Développement (IRD), Institut d'écologie et des sciences de l'environnement de Paris (iEES Paris ), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Géochimie Des Impacts (GEDI), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'Ecologie Microbienne - UMR 5557 (LEM), Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Ecole Nationale Vétérinaire de Lyon (ENVL)-VetAgro Sup - Institut national d'enseignement supérieur et de recherche en alimentation, santé animale, sciences agronomiques et de l'environnement (VAS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Department of Agricultural Land Management [Vientiane] (DALaM), Ministry of Agriculture and Forestry of Laos, ANR-13-AGRO-0007,TecItEasy,Effets conjugués de l'expansion des plantations d'arbres et du changement climatique sur le fonctionnement hydro-sédimentaire des bassins versants tropicaux de montagne: la diversité microbienne aquatique comme un proxy de la conversion d'usage des terres(2013), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-AgroParisTech-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), and Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)
Subjects: Turbidité, 010504 meteorology & atmospheric sciences, Drainage basin, 02 engineering and technology, 01 natural sciences, Panoply, Turbidity, 020701 environmental engineering, Hydrologie, Water Science and Technology, geography.geographical_feature_category, Northern uplands of Lao PDR, Inondation, Contamination biologique, Surface runoff, Ruissellement, 6. Clean water, Circulation de l'eau, S50 - Santé humaine, [SDE]Environmental Sciences, Erosion, Surface-sub surface flow separation, Storm flow, Land-use change, 0207 environmental engineering, faecal pollution [EN], Indicator bacteria, Context (language use), parasitic diseases, Escherichia coli, P10 - Ressources en eau et leur gestion, [SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, 0105 earth and related environmental sciences, Hydrology, geography, Flood myth, fungi, Fecal coliform, Fecal indicator bacteria, 13. Climate action, Environmental science
Abstract: International audience; Bacterial pathogens in surface waters threaten human health. The health risk is especially high in developing countries where sanitation systems are often lacking or deficient. Considering twelve flash-flood events sampled from 2011 to 2015 at the outlet of a 60-ha tropical montane headwater catchment in Northern Lao PDR, and using Escherichia coli as a fecal indicator bacteria, our objective was to quantify the contributions of both surface runoff and sub-surface flow to the in-stream concentration of E. coli during flood events, by (1) investigating E. coli dynamics during flood events and among flood events and (2) designing and comparing simple statistical and mixing models to predict E. coli concentration in stream flow during flood events. We found that in-stream E. coli concentration is high regardless of the contributions of both surface runoff and sub-surface flow to the flood event. However, we measured the highest concentration of E. coli during the flood events that are predominantly driven by surface runoff. This indicates that surface runoff, and causatively soil surface erosion, are the primary drivers of in-stream E. coli contamination. This was further confirmed by the step-wise regression applied to instantaneous E. coli concentration measured in individual water samples collected during the flood events, and by the three models applied to each flood event (linear model, partial least square model, and mixing model). The three models showed that the percentage of surface runoff in stream flow was the best predictor of the flood event mean E. coli concentration. The mixing model yielded a Nash-Sutcliffe efficiency of 0.65 and showed that on average, 89% of the in-stream concentration of E. coli resulted from surface runoff, while the overall contribution of surface runoff to the stream flow was 41%. We also showed that stream flow turbidity and E. coli concentration were positively correlated, but that turbidity was not a strong predictor of E. coli concentration during flood events. These findings will help building adequate catchment-scale models to predict E. coli fate and transport, and mapping the related risk of fecal contamination in a global changing context.
Published: 2021
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22. Understory Limits Surface Runoff and Soil Loss in Teak Tree Plantations of Northern Lao PDR

Author: Christian Valentin, Layheang Song, Anneke de Rouw, Chantha Oeurng, Bounchanh Lattanavongkot, Phabvilay Sounyafong, Alain Pierret, Olivier Ribolzi, Oloth Sengtaheuanghoung, Norbert Silvera, Bounsamay Soulileuth, Laurie Boithias, Bounthan Souksavath, Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Department of Agricultural Land Management [Vientiane] (DALaM), Ministry of Agriculture and Forestry of Laos, Institut d'écologie et des sciences de l'environnement de Paris (iEES Paris ), and Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)
Subjects: Wet season, lcsh:Hydraulic engineering, 010504 meteorology & atmospheric sciences, Geography, Planning and Development, teak tree plantation, South East Asia, 010501 environmental sciences, Aquatic Science, 01 natural sciences, Biochemistry, lcsh:Water supply for domestic and industrial purposes, overland flow, lcsh:TC1-978, inter-rill erosion, 0105 earth and related environmental sciences, Water Science and Technology, [SDV.EE]Life Sciences [q-bio]/Ecology, environment, lcsh:TD201-500, broom grass, soil erosion, Land use, Broom, land management, Understory, Groundwater recharge, Agronomy, understory, Soil water, Environmental science, Soil fertility, Surface runoff, South–East Asia
Abstract: Many mountainous regions of the humid tropics experience serious soil erosion following rapid changes in land use. In northern Lao People&rsquo, s Democratic Republic (PDR), the replacement of traditional crops by tree plantations, such as teak trees, has led to a dramatic increase in floods and soil loss and to the degradation of basic soil ecosystem services such as water filtration by soil, fertility maintenance, etc. In this study, we hypothesized that conserving understory under teak trees would protect soil, limit surface runoff, and help reduce soil erosion. Using 1 m2 microplots installed in four teak tree plantations in northern Lao PDR over the rainy season of 2017, this study aimed to: (1) assess the effects on surface runoff and soil loss of four understory management practices, namely teak with no understory (TNU, control treatment), teak with low density of understory (TLU), teak with high density of understory (THU), and teak with broom grass, Thysanolaena latifolia (TBG), (2) suggest soil erosion mitigation management practices, and (3) identify a field visual indicator allowing a rapid appraisal of soil erosion intensity. We monitored surface runoff and soil loss, and measured teak tree and understory characteristics (height and percentage of cover) and soil surface features. We estimated the relationships among these variables through statistics and regression analyses. THU and TBG had the smallest runoff coefficient (23% for both) and soil loss (465 and 381 g&middot, m&minus, 2, respectively). The runoff coefficient and soil loss in TLU were 35% and 1115 g&middot, 2, respectively. TNU had the highest runoff coefficient and soil loss (60%, 5455 g&middot, 2) associated to the highest crusting rate (82%). Hence, the soil loss in TBG was 14-times less than in TNU and teak tree plantation owners could divide soil loss by 14 by keeping understory, such as broom grass, within teak tree plantations. Indeed, a high runoff coefficient and soil loss in TNU was explained by the kinetic energy of rain drops falling from the broad leaves of the tall teak trees down to bare soil, devoid of plant residues, thus leading to severe soil surface crusting and soil detachment. The areal percentage of pedestal features was a reliable indicator of soil erosion intensity. Overall, promoting understory, such as broom grass, in teak tree plantations would: (1) limit surface runoff and improve soil infiltrability, thus increase soil water stock available for both root absorption and groundwater recharge, and (2) mitigate soil loss while favoring soil fertility conservation.
Published: 2020
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23. Interacting land use and soil surface dynamics control groundwater outflow in a montane catchment of the lower Mekong basin

Author: Anneke de Rouw, Phabvilay Sounyafong, Bounsamai Soulileuth, Oloth Sengtaheuanghoung, Sylvain Huon, Guillaume Lacombe, Olivier Ribolzi, Norbert Silvera, Emmanuel Mouche, Alain Pierret, Keo Oudone Latxachak, Henri Robain, Christian Valentin, Université Fédérale Toulouse Midi-Pyrénées, International Water Management Institute, International Water Management Institute, Vientiane, Biogéochimie et écologie des milieux continentaux (Bioemco), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut National de la Recherche Agronomique (INRA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-AgroParisTech-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD), Representation du Laos (IRD), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Modélisation Hydrologique (HYDRO), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), National Agriculture and Forestry Research Institute (NAFRI), Université de Toulouse (UT), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-AgroParisTech-Centre National de la Recherche Scientifique (CNRS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)
Subjects: Érosion hydrique, F08 - Systèmes et modes de culture, 0208 environmental biotechnology, 02 engineering and technology, Hydrologic connectivity, Bassin versant, Streamflow, Evapotranspiration, Electrical resistivity tomography (ERT), Hydrological modelling, P10 - Ressources en eau et leur gestion, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, ComputingMilieux_MISCELLANEOUS, P36 - Érosion, conservation et récupération des sols, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 2. Zero hunger, Hydrology, Baseflow, Ecology, Discharge, Culture itinérante, Montagne, Groundwater recharge, 15. Life on land, 6. Clean water, eau souterraine, 020801 environmental engineering, Infiltration (hydrology), Storm and inter-storm streamflow, 13. Climate action, Environmental science, Animal Science and Zoology, Tracer-based hydrograph separation, Surface runoff, Agronomy and Crop Science, Groundwater
Abstract: Groundwater contribution to streamflow sustains biodiversity and enhances ecosystem services, especially under monsoon-driven climate where stream baseflow is often the only available water resource during the dry season. We assessed how land use change influences streamflow and its groundwater contribution in a small headwater catchment subject to shifting cultivation in Montane Southeast Asia. Continuous time series of rainfall, reference evapotranspiration, groundwater level, stream discharge and electrical conductivity (EC) of surface and groundwater were monitored from 2002 to 2007. With the rainfall-runoff model GR4J, we investigated temporal changes in the hydrological behaviour of the study catchment to verify consistencies with observed land use change. An EC-based hydrograph separation method allowed estimating the groundwater contribution to 104 stormflow events. Mean soil surface crusting rates corresponding to each of the nine land uses identified in the catchment were determined using 236 standard 1-m2 micro-plots. Mean plant cover for each land use was assessed in 10 × 10-m2 plots. Bedrock topography and soil layers’ structure were assessed by electrical resistivity tomography to determine pathways of subsurface storm flows. Our results indicate that an increase in the catchment's areal percentage of fallow from 33% to 71% led to a decrease in the annual runoff coefficient from 43% to 26%. The concurrent reduction of soil crusting rate over the catchment, from 48% to 30%, increased rainwater infiltration. Consecutively, groundwater contribution to storm streamflow increased from 83% to 94%, highlighting the protective role of a dense vegetation cover against flash floods. The overall reduction of the annual basin water yield for inter-storm streamflow from 450 to 185 mm suggests that the potential gain in groundwater recharge was offset by the increased root water uptake for evapotranspiration, as confirmed by the drop in the groundwater level. This analysis illustrates how two different land uses with opposite impacts on soil permeability (i/ extensive soil surface crusting under annual crops resulting in limited runoff infiltration or ii/ fallow regrowth promoting both infiltration and evapotranspiration) both inhibit groundwater recharge. The maintenance of strips of fallow buffers between annual crop plots can slow down runoff and locally promote infiltration and groundwater recharge while limiting evapotranspiration.
Published: 2018
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24. Hydrological modeling of Fecal Indicator Bacteria in a tropical mountain catchment

Author: Laurie Boithias, Norbert Silvera, Olivier Ribolzi, Keooudone Latsachack, Kyung Hwa Cho, Chanthamousone Thammahacksa, Oloth Sengtaheuanghoung, Alain Pierret, Emma Rochelle-Newall, Minjeong Kim, Yakov Pachepsky, School of Urban and Environmental Engineering, UNIST The Genomics Institute, Géosciences Environnement Toulouse (GET), Centre National de la Recherche Scientifique (CNRS)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Institut de Recherche pour le Développement (IRD)-Centre National d'Études Spatiales [Toulouse] (CNES), Université Fédérale Toulouse Midi-Pyrénées, Centre National de la Recherche Scientifique (CNRS), Université Toulouse III - Paul Sabatier (UT3), Centre National d'Études Spatiales [Toulouse] (CNES), Department of Agricultural Land Management (DALaM), Institut de Recherche pour le Développement (IRD [France-Ouest]), Institut d'écologie et des sciences de l'environnement de Paris (IEES), Centre National de la Recherche Scientifique (CNRS)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut National de la Recherche Agronomique (INRA), Département of Agricultural Land Management (DALam), Environmental Microbial and Food Safety Laborator, USDA-ARS : Agricultural Research Service, Lao Department of Agricultural Land Management (DALaM), MSEC project (Multi-Scale Environment Changes), French National Research Agency (TecItEasy project) [ANR-13-AGRO-0007], Basic Core Technology Development Program for the Oceans, Polar Regions of the National Research Foundation (NRF) - Ministry of Science, ICT AMP, Future Planning [NRF-2016M1A5A1027457], Research Institute for Development (IRD) (Accueil de post-doctorants/Campagne), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), Department of Agricultural Land Management [Vientiane] (DALaM), Ministry of Agriculture and Forestry of Laos, Institut d'écologie et des sciences de l'environnement de Paris (iEES), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Institut National de la Recherche Agronomique (INRA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), and Université de Toulouse (UT)
Subjects: Wet season, Environmental Engineering, [SDV]Life Sciences [q-bio], 0208 environmental biotechnology, Indicator bacteria, 02 engineering and technology, Fecal Indicator Organism, Fate and transport, Deposition (geology), Feces, Dry season, Escherichia coli, SWAT, SWAT model, Tropical watershed, Waste Management and Disposal, Water Science and Technology, Civil and Structural Engineering, Hydrology, Tropical Climate, Baseflow, Bacteria, Ecological Modeling, Environmental engineering, Sediment, Soil and Water Assessment Tool, Pollution, 6. Clean water, 020801 environmental engineering, 13. Climate action, Laos, Environmental science, Water Microbiology, Surface water, Environmental Monitoring
Abstract: The occurrence of pathogen bacteria in surface waters is a threat to public health worldwide. In particular, inadequate sanitation resulting in high contamination of surface water with pathogens of fecal origin is a serious issue in developing countries such as Lao P.D.R. Despite the health implications of the consumption of contaminated surface water, the environmental fate and transport of pathogens of fecal origin and their indicators (Fecal Indicator Bacteria or FIB) are still poorly known in tropical areas. In this study, we used measurements of flow rates, suspended sediments and of the FIB Escherichia coli (E. coli) in a 60-ha catchment in Northern Laos to explore the ability of the Soil and Water Assessment Tool (SWAT) to simulate watershed-scale FIB fate and transport. We assessed the influences of 3 in-stream processes, namely bacteria deposition and resuspension, bacterial regrowth, and hyporheic exchange (i.e. transient storage) on predicted FIB numbers. We showed that the SWAT model in its original version does not correctly simulate small E. coli numbers during the dry season. We showed that model's performance could be improved when considering the release of E. coli together with sediment resuspension. We demonstrated that the hyporheic exchange of bacteria across the Sediment-Water Interface (SWI) should be considered when simulating FIB concentration not only during wet weather, but also during the dry season, or baseflow period. In contrast, the implementation of the regrowth process did not improve the model during the dry season without inducing an overestimation during the wet season. This work thus underlines the importance of taking into account in-stream processes, such as deposition and resuspension, regrowth and hyporheic exchange, when using SWAT to simulate FIB dynamics in surface waters.
Published: 2017
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25. Use of the Dixon-Tyree stem hygrometer in a rubber tree plantation

Author: Norbert Silvera, Jerzy Jan Nizinski, Marc Lointier, and Jean-Pierre Montoroi
Subjects: MODELE MATHEMATIQUE, Hydrology, Atmospheric Science, Global and Planetary Change, POTENTIEL HYDRIQUE, Hygrometer, Xylem, TRONC, Forestry, Cote d ivoire, Xylem water potential, HYGROMETRIE, RACINE, APPAREIL DE MESURE, Natural rubber, visual_art, PLANTATION, visual_art.visual_art_medium, Environmental science, CAOUTCHOUC, FEUILLE, Agronomy and Crop Science, METHODOLOGIE, VARIATION JOURNALIERE, NECROSE
Abstract: The Dixon-Tyree stem hygrometer has hitherto been used primarily indoors in controlled conditions. We used it, and the leaf pressure chamber, to measure water potentials in plantation rubber trees outside in the Cote d’Ivoire (May and September 2004). Measurements of stem and root xylem water potentials were considered to be reliable, provided they complied with technical constraints that we specify. The stem hygrometer is non-destructive if the sensor is well installed, and provides measurements for two to three weeks without intervention, although the initial measurements are sometimes erroneous.
Published: 2013
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26. Effect of land use and hydrological processes on Escherichia coli concentrations in streams of tropical, humid headwater catchments

Author: Laurie Boithias, Bounsamay Soulileuth, Norbert Silvera, Olivier Ribolzi, Pem Sisouvanh, Nikom Hmaimum, Keooudone Latsachack, Henri Robain, Hai Tran Sy, Rinh Pham Dinh, Marion Viguier, Jean-Louis Janeau, Piyapong Naporn, Christian Valentin, Emma Rochelle-Newall, Chanthamousone Thammahacksa, Alain Pierret, Institut d'écologie et des sciences de l'environnement de Paris (iEES), Institut National de la Recherche Agronomique (INRA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS), Géosciences Environnement Toulouse (GET), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement, Partenaires INRAE, Soils & Fertilizers Res Inst, Duc Thang Ward, Hanoi, Vietnam, Natl Pk Wildlife & Plant Conservat Dept NPD, 61 Phaholyotin Rd, Bangkok 10900, Thailand, National Park, Wild Life and Plant Conservation Department (DNP), National Park Wild Life and Plant Conservation Department, National University of Laos, French ANR 'Teciteasy' [ANR-13-AGRO-0007], French Institut de Recherche pour le Developpement (IRD) through the ECOFILTER project (LMI LUSES), UMR iEES-Paris, UMR GET, Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut National de la Recherche Agronomique (INRA), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), and Rochelle-Newall, Emma
Subjects: Rain, [SDV]Life Sciences [q-bio], 0208 environmental biotechnology, 02 engineering and technology, 010501 environmental sciences, 01 natural sciences, Feces, contamination, afforestation, Vegetation type, Dry season, Multidisciplinary, Ecology, Agriculture, stormwater runoff, health, Vegetation, Thailand, field, 6. Clean water, Catchment hydrology, Vietnam, Laos, [SDE]Environmental Sciences, Seasons, Water Microbiology, Environmental Monitoring, Wet season, fecal indicator bacteria, STREAMS, Article, Hydrology (agriculture), Water Supply, Escherichia coli, Animals, Humans, Developing Countries, soils, 0105 earth and related environmental sciences, northern vietnam, Hydrology, Tropical Climate, rivers, waters, Humidity, 15. Life on land, Bacterial Load, 020801 environmental engineering, 13. Climate action, Environmental science, Surface runoff
Abstract: Lack of access to clean water and adequate sanitation continues to be a major brake on development. Here we present the results of a 12-month investigation into the dynamics of Escherichia coli, a commonly used indicator of faecal contamination in water supplies, in three small, rural catchments in Laos, Thailand and Vietnam. We show that land use and hydrology are major controlling factors of E. coli concentrations in streamwater and that the relative importance of these two factors varies between the dry and wet seasons. In all three catchments, the highest concentrations were observed during the wet season when storm events and overland flow were highest. However, smaller peaks of E. coli concentration were also observed during the dry season. These latter correspond to periods of intense farming activities and small, episodic rain events. Furthermore, vegetation type, through land use and soil surface crusting, combined with mammalian presence play an important role in determining E. coli loads in the streams. Finally, sampling during stormflow revealed the importance of having appropriate sampling protocols if information on maximum contamination levels is required as grab sampling at a fixed time step may miss important peaks in E. coli numbers.
Published: 2016
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27. Use of fallout radionuclides (7Be, 210Pb) to estimate resuspension of Escherichia coli from streambed sediments during floods in a tropical montane catchment

Author: Norbert Silvera, Emma Rochelle-Newall, Oloth Sengtaheuanghoung, Chanthamousone Thammahacksac, Olivier Evrard, Thierry Henri-des-Tureaux, Olivier Ribolzi, Sylvain Huon, Géosciences Environnement Toulouse (GET), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Géochimie Des Impacts (GEDI), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Institut d'écologie et des sciences de l'environnement de Paris (iEES), Institut National de la Recherche Agronomique (INRA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD), Department of Agricultural Land Management (DALaM), Lao Department of Agriculture Land Management (DALAM), MSEC project (Multi-Scale Environment Changes), French Centre National de la Recherche Scientifique EC2CO/BIOHEFECT program (Belcrue project), French Centre National de la Recherche Scientifique EC2CO/BIOHEFECT program (Belkong project), French National Research Agency [ANR-13-AGRO-0007], ANR-13-AGRO-0007,TecItEasy,Effets conjugués de l'expansion des plantations d'arbres et du changement climatique sur le fonctionnement hydro-sédimentaire des bassins versants tropicaux de montagne: la diversité microbienne aquatique comme un proxy de la conversion d'usage des terres(2013), Centre National de la Recherche Scientifique (CNRS)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Institut de Recherche pour le Développement (IRD)-Centre National d'Études Spatiales [Toulouse] (CNES), Patrimoines Locaux et Gouvernance (PALOC), Muséum national d'Histoire naturelle (MNHN)-Institut de Recherche pour le Développement (IRD), Institut d'écologie et des sciences de l'environnement de Paris (IEES), Centre National de la Recherche Scientifique (CNRS)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut National de la Recherche Agronomique (INRA), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), and Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)
Subjects: Radioactive Fallout, Geologic Sediments, Water flow, Rain, Health, Toxicology and Mutagenesis, 0208 environmental biotechnology, Hydrograph, 02 engineering and technology, STREAMS, 010501 environmental sciences, South East Asia, 01 natural sciences, Feces, Overland flow, FIB, Rivers, Streamflow, Escherichia coli, Hydrological modelling, Environmental Chemistry, Water Pollutants, [SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, Radioisotopes, Hydrology, Beryllium-7, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Tropical Climate, General Medicine, 15. Life on land, Pollution, [SDV.MP.BAC]Life Sciences [q-bio]/Microbiology and Parasitology/Bacteriology, Floods, 6. Clean water, 020801 environmental engineering, Lead, 13. Climate action, Erosion, Lead-210, Land use, Beryllium, Surface runoff, Geology, Groundwater, Environmental Monitoring, Return flow
Abstract: Consumption of water polluted by faecal contaminants is responsible for 2 million deaths annually, most of which occur in developing countries without adequate sanitation. In tropical aquatic systems, streambeds can be reservoirs of persistent pathogenic bacteria and high rainfall can lead to contaminated soils entering streams and to the resuspension of sediment-bound microbes in the streambed. Here, we present a novel method using fallout radionuclides ((7)Be and (210)Pbxs) to estimate the proportions of Escherichia coli, an indicator of faecal contamination, associated with recently eroded soil particles and with the resuspension of streambed sediments. We show that using these radionuclides and hydrograph separations we are able to characterize the proportion of particles originating from highly contaminated soils and that from the resuspension of particle-attached bacteria within the streambed. We also found that although overland flow represented just over one tenth of the total flood volume, it was responsible for more than two thirds of the downstream transfer of E. coli. We propose that data obtained using this method can be used to understand the dynamics of faecal indicator bacteria (FIB) in streams thereby providing information for adapted management plans that reduce the health risks to local populations. Graphical Abstract Graphical abstract showing (1) the main water flow processes (i.e. overland flow, groundwater return flow, blue arrows) and sediment flow components (i.e. resuspension and soil erosion, black arrows) during floods in the Houay Pano catchment; (2) the general principle of the method using fallout radionuclide markers (i.e. (7)Be and (210)Pbxs) to estimate E. coli load from the two main sources (i.e. streambed resuspension vs soil surface washoff); and 3) the main results obtained during the 15 May 2012 storm event (i.e. relative percentage contribution of each process to the total streamflow, values in parentheses).
Published: 2016
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28. Contradictory hydrological impacts of afforestation in the humid tropics evidenced by long-term field monitoring and simulation modelling

Author: Didier Orange, Olivier Ribolzi, Jean-Louis Janeau, Henri Robain, Alain Pierret, Christian Valentin, Guillaume Lacombe, Toan Tran Duc, Keoudone Latsachak, Adrien Taccoen, Rinh Pham Dinh, Anneke de Rouw, Phouthamaly Sengphaathith, Emmanuel Mouche, Norbert Silvera, Bounsamai Soulileuth, Oloth Sengtaheuanghoung, International Water Management Institute [CGIAR, Laos] (IWMI), International Water Management Institute [CGIAR, Sri Lanka] (IWMI), Consultative Group on International Agricultural Research [CGIAR] (CGIAR)-Consultative Group on International Agricultural Research [CGIAR] (CGIAR), Géosciences Environnement Toulouse (GET), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), Institut d'écologie et des sciences de l'environnement de Paris (iEES Paris ), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Soils and Fertilizers Research Institute (SFRI), Vietnam Academy of Agricultural Sciences (VAAS), Ecologie fonctionnelle et biogéochimie des sols et des agro-écosystèmes (UMR Eco&Sols), Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA), Laboratoire d'Etudes des Ressources Forêt-Bois (LERFoB), Ecole Nationale du Génie Rural, des Eaux et des Forêts (ENGREF)-Institut National de la Recherche Agronomique (INRA), University of Arizona, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Modélisation Hydrologique (HYDRO), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Ministry of Agriculture and Forestry of Laos, Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Sorbonne Université (SU)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Géosciences Environnement Toulouse ( GET ), Institut de Recherche pour le Développement ( IRD ) -Université Paul Sabatier - Toulouse 3 ( UPS ) -Observatoire Midi-Pyrénées ( OMP ) -Centre National de la Recherche Scientifique ( CNRS ), Institut d'écologie et des sciences de l'environnement de Paris ( IEES ), Institut National de la Recherche Agronomique ( INRA ) -Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Université Paris-Est Créteil Val-de-Marne - Paris 12 ( UPEC UP12 ) -Centre National de la Recherche Scientifique ( CNRS ), Institut de Recherche pour le Développement ( IRD [France-Ouest] ), Centre de Recherches Interculturelles sur les Domaines Anglophones et Francophones ( CRIDAF ), Université Paris 13 ( UP13 ) -Université Sorbonne Paris Cité ( USPC ), Laboratory of Molecular Neuro-oncology, Howard Hughes Medical Institute ( HHMI ) -The Rockefeller University, Representation du Laos ( IRD ), Unité GEOVAST, Institut de Recherche pour le Développement ( IRD ), Laboratoire de minéralogie, cristallographie de Paris ( LMCP ), Université Pierre et Marie Curie - Paris 6 ( UPMC ) -IPG PARIS-Université Paris Diderot - Paris 7 ( UPD7 ) -Centre National de la Recherche Scientifique ( CNRS ), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] ( LSCE ), Université de Versailles Saint-Quentin-en-Yvelines ( UVSQ ) -Commissariat à l'énergie atomique et aux énergies alternatives ( CEA ) -Université Paris-Saclay-Centre National de la Recherche Scientifique ( CNRS ), Department of Agricultural Land Management ( DALaM ), Soils and Fertilizers Research Institute ( SFRI ), VAAS, Laboratoire Chrono-environnement ( LCE ), Université Bourgogne Franche-Comté ( UBFC ) -Université de Franche-Comté ( UFC ) -Centre National de la Recherche Scientifique ( CNRS ), Université Fédérale Toulouse Midi-Pyrénées-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Institut d'écologie et des sciences de l'environnement de Paris (IEES), Centre National de la Recherche Scientifique (CNRS)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut National de la Recherche Agronomique (INRA), Institut de Recherche pour le Développement (IRD [France-Ouest]), Centre de Recherches Interculturelles sur les Domaines Anglophones et Francophones (CRIDAF), Université Paris 13 (UP13)-Université Sorbonne Paris Cité (USPC), Howard Hugues Medical Institute-The Rockefeller University, Representation du Laos (IRD), Institut de Recherche pour le Développement (IRD), Laboratoire de minéralogie, cristallographie de Paris (LMCP), Université Pierre et Marie Curie - Paris 6 (UPMC)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Université Paris-Saclay-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS), Department of Agricultural Land Management (DALaM), Laboratoire Chrono-environnement - UFC (UMR 6249) (LCE), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Centre National de la Recherche Scientifique (CNRS)-Université de Franche-Comté (UFC), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), and Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS)
Subjects: [ SDU.OCEAN ] Sciences of the Universe [physics]/Ocean, Atmosphere, 010504 meteorology & atmospheric sciences, Tree planting, 0208 environmental biotechnology, Conservation des sols, 02 engineering and technology, 01 natural sciences, lcsh:Technology, Water balance, Shifting cultivation, Tectona grandis, Afforestation, Forêt tropicale humide, lcsh:Environmental technology. Sanitary engineering, Hydrologie, ComputingMilieux_MISCELLANEOUS, lcsh:Environmental sciences, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 2. Zero hunger, lcsh:GE1-350, lcsh:Geography. Anthropology. Recreation, Plantation forestière, Reconstitution forestière, lcsh:TD1-1066, Water conservation, Conservation de l'eau, Streamflow, [ SDU.ENVI ] Sciences of the Universe [physics]/Continental interfaces, environment, Hydrometeorology, P10 - Ressources en eau et leur gestion, [SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, 0105 earth and related environmental sciences, P36 - Érosion, conservation et récupération des sols, Hydrology, lcsh:T, Régénération naturelle, 15. Life on land, K10 - Production forestière, 020801 environmental engineering, Water resources, lcsh:G, 13. Climate action, Environmental science
Abstract: The humid tropics are exposed to an unprecedented modernisation of agriculture involving rapid and mixed land-use changes with contrasted environmental impacts. Afforestation is often mentioned as an unambiguous solution for restoring ecosystem services and enhancing biodiversity. One consequence of afforestation is the alteration of streamflow variability which controls habitats, water resources, and flood risks. We demonstrate that afforestation by tree planting or by natural forest regeneration can induce opposite hydrological changes. An observatory including long-term field measurements of fine-scale land-use mosaics and of hydrometeorological variables has been operating in several headwater catchments in tropical southeast Asia since 2000. The GR2M water balance model, repeatedly calibrated over successive 1-year periods and used in simulation mode with the same year of rainfall input, allowed the hydrological effect of land-use change to be isolated from that of rainfall variability in two of these catchments in Laos and Vietnam. Visual inspection of hydrographs, correlation analyses, and trend detection tests allowed causality between land-use changes and changes in seasonal streamflow to be ascertained. In Laos, the combination of shifting cultivation system (alternation of rice and fallow) and the gradual increase of teak tree plantations replacing fallow led to intricate streamflow patterns: pluri-annual streamflow cycles induced by the shifting system, on top of a gradual streamflow increase over years caused by the spread of the plantations. In Vietnam, the abandonment of continuously cropped areas combined with patches of mix-trees plantations led to the natural re-growth of forest communities followed by a gradual drop in streamflow. Soil infiltrability controlled by surface crusting is the predominant process explaining why two modes of afforestation (natural regeneration vs. planting) led to opposite changes in streamflow regime. Given that commercial tree plantations will continue to expand in the humid tropics, careful consideration is needed before attributing to them positive effects on water and soil conservation.
Published: 2016
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29. Spatial and temporal assessment of linear erosion in catchments under sloping lands of northern Laos

Author: Norbert Silvera, Vincent Chaplot, Christian Valentin, and E. Coadou le Brozec
Subjects: Rill, Hydrology, geography, Watershed, geography.geographical_feature_category, Land use, Drainage basin, Erosion, Environmental science, Slash-and-burn, Catchment area, Soil conservation, Earth-Surface Processes
Abstract: Linear erosion (LE), including rilling and gullying, has been identified as the major problem for sustainable agriculture in steepland areas. It causes severe environmental, economic, and social impacts. This issue is even more crucial in those areas undergoing rapid changes in land use, as for example northern Laos, and may dramatically affect soil conservation. Despite an increasing interest in the sloping lands of tropical areas, field evaluations of LE are still infrequent. Furthermore, the controlling environmental factors of topography, land use, climate and soils at the catchment level are seldom analysed. Our main objective was to quantify the spatial and temporal variations of LE at the catchment level and at a yearly basis. The study was conducted in a 0.62 km 2 watershed of Laos (Luang Prabang province) representative of the slash and burn systems of sloping lands. Linear erosion was monitored from 2001 to 2003 within 9 sub-catchments of differing surface areas, topographic characteristics and land use. The length, depth and width of the linear erosion features were recorded every 5-m from their headcuts to their outlets in order to estimate the total catchment LE. 52 linear features, mainly rills, were formed or developed within the study area with a mean erosion rate of 1.3 Mg ha − 1 y − 1 . LE rates ranged between 0.1 Mg ha − 1 y − 1 in 2003 to 2.4 Mg ha − 1 y − 1 in 2001. LE features mostly occurred within croplands where erosion rates reached 18 Mg ha − 1 y − 1 . In 2001 and 2002 there was a significant correlation between LE and the proportion of the catchment area under crops ( r = 0.88 and r = 0.69, respectively). However this was not the case in 2003 when few rills developed. In 2002 only, LE correlated well with the catchment surface area, the mean slope gradient and the sub-catchment perimeter confirming the non-constancy of LE landscape relation under varying rainstorm conditions. A linear regression model for LE prediction at the catchment level, generated from 2001 data, was able to explain 78% of LE variance for the 9 sub-catchments. However, this model was unable to predict accurately LE for 2002 and 2003 (ME > 5 Mg ha − 1 y − 1 ). This method for quantifying the linear erosion at the catchment level and some of its controlling factors can also be used for prediction over larger areas since topography and land use data, closely correlated with LE, are easily accessible.
Published: 2005
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30. Microrelief induced by tillage: measurement and modelling of Surface Storage Capacity

Author: Olivier Planchon, Jean-Marc Lapetite, Norbert Silvera, and Michel Esteves
Subjects: DRAINAGE, Flow (psychology), EAU DU SOL, TRAVAIL DU SOL, Soil science, MODELE NUMERIQUE D'ELEVATION, ETAT DE SURFACE DU SOL, COMPACITE, STOCKAGE, Perpendicular, MESURE, Boundary value problem, Digital elevation model, ANALYSE NUMERIQUE, Earth-Surface Processes, Mathematics, Hydrology, MICRORELIEF, ECOULEMENT DE SURFACE, MODELISATION, PRATIQUE CULTURALE, Exponential function, Tillage, Volume (thermodynamics), PENTE, Surface water
Abstract: The micro-topography of a groundnut plot in Senegal has been recorded over a full cultivation cycle, using an automated device able to measure 16.2 m2 at every 5 cm with an accuracy of 1 mm. Tillage is horse drawn, perpendicular to the general slope, and generates oriented microreliefs. Surface Storage Capacity (SSC) was calculated on both raw and slope-detrended surfaces. Additionally, various boundary conditions (BC) were used: no-wall; three-wall (up, left and right); or mirror (the Digital Elevation Model (DEM) surrounded by eight alternately reversed images of itself). SSC is more affected by these variants than by the variations of microrelief itself. Whatever the calculation method, SSC (as well as random roughness), follows a decreasing exponential with cumulated rainfall, but the coefficients of the exponential differ widely to each other. This suggests that SSC values could be of little use when they are obtained on various slopes, arbitrarily detrended or not, and calculated with arbitrary BC. We suggest a simple geometric model to characterise the way microrelief empties as the slope increases. The model has two calibrated depth-ratio parameters, one in each direction. It gives a more coherent framework for calculation and use of SSC. The model was applied to one of the DEMs of the data set, sampled after the first rain following hoeing. With the mirror-BC and detrended slope, SSC was 3.6 mm. Microrelief was found to behave in the same proportions, when tilted, than a tetrahedral container 94 times wider than deeper in the tillage direction and 11 times perpendicularly. This model represents the volume of surface water that cannot flow in any direction. With three-wall-BC, SSC was 6.7 mm, 1.4 mm remaining on the plot whatever the slope angle, and 5.3 mm behaving the same as a container 69 times wider than deeper. A possible use of this model is illustrated with an attempt to upscale the sampled plot to the watershed to which it belongs.
Published: 2002
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31. Relationship between raindrop erosion and runoff erosion under simulated rainfall in the Sudano-Sahel: consequences for the spread of nematodes by runoff

Author: Patrice Cadet, Jean-Marc Lapetite, Olivier Planchon, Norbert Silvera, and Michel Esteves
Subjects: Hydrology, business.product_category, SOL, Geography, Planning and Development, MICRORELIEF, Sediment, NEMATODE, INFESTATION, Bulk density, Plough, PLUIE, Dry season, Soil water, Earth and Planetary Sciences (miscellaneous), Erosion, ETUDE EXPERIMENTALE, Carrying capacity, Environmental science, EROSION HYDRIQUE, ECOULEMENT, SIMULATION DE PLUIE, DISTRIBUTION SPATIALE, business, Surface runoff, Earth-Surface Processes
Abstract: This paper presents a rainfall simulation experiment carried out on three 50 m2 plots in the Senegalese groundnut belt. One plot was not cultivated. Groundnut and millet had previously been grown in the other two. The experiment consisted of three rain events applied over 5 days at the end of the dry season. Erosion was monitored inside the plots by the use of a relief meter and, at their outlets, by sampling the discharge. The number of indigenous nematodes, and an exotic species introduced before the first rain event, was monitored in the soil and in the discharge. This experiment allows, for the first time, a set of simple hypotheses to be proposed to explain the spread of nematodes by the runoff: raindrop impacts on the soil surface set them in suspension; then, their low bulk density and their relatively large size do not allow them to settle when the raindrops shake the water surface. Thus, nematodes follow the flow path where they are as far as its velocity remains significant. The biological aspects are decisive in the mobility of nematodes, which can vary by a factor of 100 depending on the trophic groups. A very high raindrop erosion occurred during the experiment, up to 60 tons per hectare for the first rain event after hoeing. This represents more than 40 per cent of the volume of soil previously moved by soil work. The geometric properties of the plough, and their hydraulic consequences, appear very ephemeral. And yet these large movements of soil inside the plots are little related to the sediment load at the outlet, which follows its own rules. Analysis of the results indicates that the carrying capacity of the runoff at the scale of 10 m2, on gentle slopes ploughed perpendicular to the slope, could not be directly calculable from the discharge. It could depend on the history of past discharges because the shape of the flow paths, which condition their carrying capacity, permanently interacts with the discharge. These interactions could explain the great difficulties encountered by the erosion models in the case of low discharges on non-cohesive soils. Copyright © 2000 John Wiley & Sons, Ltd.
Published: 2000
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32. Comparison of roughness models to simulate overland flow and tracer transport experiments under simulated rainfall at plot scale

Author: J. Patin, Emmanuel Mouche, Patrick Richard, Olivier Planchon, Norbert Silvera, C. Mügler, Sylvain Weill, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Modélisation Hydrologique (HYDRO), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Laboratoire d'étude des Interactions Sol - Agrosystème - Hydrosystème (UMR LISAH), Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), BIOEMCO c/o Center for Water Resources Research, SAEES, Institut de Recherche pour le Développement (IRD), Biogéochimie et écologie des milieux continentaux (Bioemco), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut National de la Recherche Agronomique (INRA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-AgroParisTech-Centre National de la Recherche Scientifique (CNRS), RIDES project, ECCO, Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro Montpellier, École normale supérieure - Paris (ENS-PSL), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-AgroParisTech-Centre National de la Recherche Scientifique (CNRS)
Subjects: 010504 meteorology & atmospheric sciences, Scale (ratio), [SDE.MCG]Environmental Sciences/Global Changes, Flow (psychology), 0207 environmental engineering, Roughness model, Hydrograph, 02 engineering and technology, Surface finish, Rainfall-simulation, 01 natural sciences, Power law, Tracer injection, [SPI.MECA.MEFL]Engineering Sciences [physics]/Mechanics [physics.med-ph]/Fluids mechanics [physics.class-ph], TRACER, [SDU.STU.HY]Sciences of the Universe [physics]/Earth Sciences/Hydrology, 020701 environmental engineering, 0105 earth and related environmental sciences, Water Science and Technology, Hydrology, [SDE.IE]Environmental Sciences/Environmental Engineering, Mechanics, Flow velocity, Friction law, Environmental science, Surface runoff
Abstract: International audience; The Saint-Venant equations have consistently proved capable of accurately simulating hydrographs at plot scale. However, recent works showed that even though the hydrograph is satisfyingly reproduced, the flow velocity field within the plot might be wrong, with the highest velocity largely underestimated. Moreover, the choice of roughness models to be used in the Saint-Venant equations is most often done in the purpose of increasing the hydrograph quality, while the actual travel time of water is ignored. This paper presents a tracer experiment made on a 10-m by 4-m rainfall simulation plot, where travel time and tracer mass recovery as well as local flow velocity have been measured. Four roughness models are tested: (i) Darcy-Weisbach's model, (ii) Lawrence's model, (iii) Manning's model with a constant roughness coefficient, and (iv) Manning's model with a variable roughness coefficient which decreases as a power law of the runoff water depth. Models with a constant friction factor largely underestimate high velocities. Moreover, they are not able to simulate tracer travel-times. Lawrence's model correctly simulates low and high velocities as well as tracer breakthrough curves. However, a specific set of parameters are required for each breakthrough curve from the same experiment. The best results are obtained with the Manning's model with a water-depth dependent roughness coefficient: simulated velocities are consistent with measurements, and a single set of parameters captures the entire set of breakthrough curves, as well as tracer mass recovery. The study reported here brings the following findings: (i) roughness coefficient is flow-dependent, (ii) faithful simulation of the velocity fields does not imply a good prediction of travel time and mass recovery, (iii) the best model is a Manning type model with a roughness coefficient which decreases as a power law of water depth. The full dataset used in this work is available on request. It can be used as benchmark for overland flow and transport models.
Published: 2011
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33. Impact of slope gradient on soil surface features and infiltration on steep slopes in northern Laos

Author: Jean-Pierre Thiébaux, Olivier Ribolzi, Christian Valentin, Oloth Sengtaheuanghoung, K.O. Latsachack, Emmanuel Mouche, L.M. Bresson, Norbert Silvera, J. Patin, Géosciences Environnement Toulouse (GET), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Environnement et Grandes Cultures (EGC), AgroParisTech-Institut National de la Recherche Agronomique (INRA), International Water Management Institute [CGIAR, Laos] (IWMI), International Water Management Institute [CGIAR, Sri Lanka] (IWMI), Consultative Group on International Agricultural Research [CGIAR] (CGIAR)-Consultative Group on International Agricultural Research [CGIAR] (CGIAR), Modélisation Hydrologique (HYDRO), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Agiculture Land Research Center (ALRC), National Agriculture and Forest Research Institute, Office of Science and Land Development, Institut de Recherche pour le Développement (IRD), Biogéochimie et écologie des milieux continentaux (Bioemco), École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut National de la Recherche Agronomique (INRA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-AgroParisTech-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Institut de Recherche pour le Développement (IRD)-Centre National d'Études Spatiales [Toulouse] (CNES), Université Paris-Saclay-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Centre National de la Recherche Scientifique (CNRS), International Water Management Institute, Centre National de la Recherche Scientifique (CNRS)-AgroParisTech-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut National de la Recherche Agronomique (INRA)-École normale supérieure - Paris (ENS Paris), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Institut National de la Recherche Agronomique (INRA)-AgroParisTech, Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Paris (ENS-PSL), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Université Pierre et Marie Curie - Paris 6 (UPMC)-AgroParisTech-Centre National de la Recherche Scientifique (CNRS)
Subjects: [SDV.SA]Life Sciences [q-bio]/Agricultural sciences, 010504 meteorology & atmospheric sciences, Compaction, STEEP SLOPES, 01 natural sciences, Hydraulic conductivity, Hillslope processes, Vegetation and slope stability, 0105 earth and related environmental sciences, Earth-Surface Processes, Hydrology, RAINFALL SIMULATION, SURFACE DU SOL, HILLSLOPE PROCESSES, HYDROLOGIE, Infiltration, 04 agricultural and veterinary sciences, 15. Life on land, Runoff generation, Infiltration (HVAC), Bulk density, 6. Clean water, Steep slopes, INFILTRATION, Loam, Soil water, 040103 agronomy & agriculture, Rainfall simulation, 0401 agriculture, forestry, and fisheries, RUNOFF GENERATION, Surface runoff, Geology
Abstract: It was recently demonstrated that, infiltration into mountain-tilled soils with highly stable microaggregates, increases with increasing slope gradient. In this work we investigate the processes that underpin this phenomenon by means of field experiments and modelling. The study area is located in northern Laos. Rainfall simulations were conducted in two 1-m 2 plots using a portable field simulator. The drop size distribution and kinetic energy were similar to that occurring on the occasion of tropical downpours. Soils exhibited a clay loam texture and very similar organic matter contents across experimental plots, but differed greatly in slope gradient (30% and 75%). Runoff water samples were collected at intervals ranging from 1 to 3 min, depending on the runoff intensity. Plots microtopography was measured before and after rainfall simulations using an automatic surface roughness meter on a 1-cm grid. High-resolution bulk density images were obtained from soil slices using a standard X-ray generator. Final infiltration rates of 6 and 21 mm h −1 ; soil detachment of 667 and 310 g m −2 ; surface lowering due to soil loss of 0.82 and 0.38 mm; surface lowering due to compaction of 1.21 and 0.90 mm; percentage area with sieving crust of 36% and 90%; percentage area with erosion crust of 63% and 0%; were obtained for the 30% and 75% slopes, respectively. Three main conclusions can be drawn from this work: (1) high intensity rainfall can rapidly transform soil surface features of steep bare soil; (2) on steeper slopes, the micro-relief tends to form micro-terraces much more pervious and less erodible than the ripple-like roughness that formed on gentler slopes; and (3) there was a more pronounced lowering of the soil surface due to compaction and denser microlayers on gentler slopes. The latter conclusion confirms the hypothesis that higher effective rainfall intensity is responsible for the formation of less permeable erosion crusts under 30% slope gradients while more permeable structural crusts develop under 75% slope gradients. The runoff results were modelled with the Green and Ampt model which accounts for time evolution of soil hydraulic conductivity. This modelling shows that soil is undoubtedly non homogeneous, evolves with time and that infiltration kinetics is slower and soil permeability greater for the 75% slope.
Published: 2011
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34. Measurement and modelling of high-resolution flow-velocity data under simulated rainfall on a low-slope sandy soil

Author: Norbert Silvera, John Wainwright, David Favis-Mortlock, Guillaume Nord, Olivier Ribolzi, Lucile Tatard, Chi Hua Huang, Olivier Planchon, and Michel Esteves
Subjects: geography, geography.geographical_feature_category, Hydraulics, Hydrograph, Soil science, Plume, law.invention, Rill, Kinematic wave, Infiltration (hydrology), symbols.namesake, Flow velocity, law, Froude number, symbols, Geotechnical engineering, Geology, Water Science and Technology
Abstract: The study presented here is focussed on the question of the hydraulic nature of the threshold that allows a rill to start. A rainfall-simulation experiment was carried out to produce high-resolution flow-velocity data. The experiment employed a 10 m x 4 m experimental plot with a 1% slope, which had been previously eroded and had a small rill formed in the middle. The experiment consisted of a 2 h 15'-Long rainfall at a constant intensity of 69 mm h(-1). Surface elevation was measured before rainfall at a horizontal resolution of 2.5 cm across, and 5 cm along the slope direction. During rainfall, flow-velocities were measured at 68 locations on the plot with the salt velocity gauge technology, an automated, miniaturized device based on the inverse modelling of the propagation of a salt plume. The experiment led to the collection of flow-velocity measurements which are novel in three ways: (i) the small size of the measured section, which was only 10-cm long and 1-cm wide, (ii) the wide range of measured flow-velocities, which ranged from 0.006 m s(-1) to 0.27 m s(-1) and, (iii) the large number of measured locations. The flow-velocity field was simulated with three models: PSEM_2D solves the Saint-Venant equations in 2D, MAHLERAN uses a 1D kinematic wave in the slope direction coupled with a 2D flow-routing algorithm, and Rillgrow2, which involves an empirical runoff algorithm that is close in principle to the diffusion-wave equation in 2D. The Darcy-Weisbach friction factor (ff) and the infiltration parameters were calibrated in all cases to investigate the capabilities of the different models to reproduce flow hydraulics compatible with the onset of rilling. In a first set of numerical experiments, ff was set uniform, and calibration used only the hydrograph. The comparison of simulated and observed flow-velocity field showed that PSEM_2D was the most satisfying model, at the cost of longer computational time. MAHLERAN gave surprisingly good results with regards to the simplicity of the model and its low computational needs. However, all models largely underestimated the highest velocity values, located in the rill. Furthermore, none of the models was able to simulate the Reynolds (Re) and Froude (Fr) numbers. The next numerical experiment was done with PSEM_2D. Non-uniform ff values were calibrated by fitting the simulated flow-velocity field to the observed one. The latter simulation produced realistic simulations of Re and Fr. The hydraulic conditions at the transition from interrill flow to rill flow are discussed. The results support the theory that supercritical flows are a necessary condition for a rill to emerge from a smooth surface.
Published: 2008

35. Accuracy of interpolation techniques for the derivation of digital elevation models in relation to landform types and data density

Author: Norbert Silvera, Vincent Chaplot, Frédéric Darboux, Konngkeo Phachomphon, Hocine Bourennane, Sophie Leguédois, Institut de Recherche pour le Développement (IRD), National Agriculture and Forestry Research Institute (NAFRI), Unité de recherche Science du Sol (USS), Institut National de la Recherche Agronomique (INRA), Institut de Recherche pour le Développement, and Partenaires INRAE
Subjects: 010504 meteorology & atmospheric sciences, Mean squared error, [SDV]Life Sciences [q-bio], 0207 environmental engineering, Soil science, 02 engineering and technology, 01 natural sciences, landform type, SAMPLING DENSITY, LANDFORM TYPE, Kriging, Inverse distance weighting, Radial basis function, 020701 environmental engineering, Digital elevation model, 0105 earth and related environmental sciences, Earth-Surface Processes, spatial scale, geography, geography.geographical_feature_category, INTERPOLATION METHOD, Landform, interpolation method, DEM, 15. Life on land, Spline (mathematics), sampling density, [SDE]Environmental Sciences, Spatial ecology, SPATIAL SCALE, Cartography, Geology
Abstract: One of the most important scientific challenges of digital elevation modeling is the development of numerical representations of large areas with a high resolution. Although there have been many studies on the accuracy of interpolation techniques for the generation of digital elevation models (DEMs) in relation to landform types and data quantity or density, there is still a need to evaluate the performance of these techniques on natural landscapes of differing morphologies and over a large range of scales. To perform such an evaluation, we investigated a total of six sites, three in the mountainous region of northern Laos and three in the more gentle landscape of western France, with various surface areas from micro-plots, hillslopes, and catchments. The techniques used for the interpolation of point height data with density values from 4 to 109 points/km(2) include: inverse distance weighting (IDW), ordinary kriging (OK), universal kriging (UK), multiquadratic radial basis function (MRBF), and regularized spline with tension (RST). The study sites exhibited coefficients of variation (CV) of altitude between 12% and 78%, and isotropic to anisotropic spatial structures with strengths from weak (with a nugget/sill ratio of 0.8) to strong (0.01). Irrespective of the spatial scales or the variability and spatial structure of altitude, few differences existed between the interpolation methods if the sampling density was high, although MRBF performed slightly better. However, at lower sampling densities, kriging yielded the best estimations for landscapes with strong spatial structure, low CV and low anisotropy, while RST yielded the best estimations for landscapes with low CV and weak spatial structure. Under conditions of high CV, strong spatial structure and strong anisotropy, IDW performed slightly better than the other method. The prediction errors in height estimation are discussed in relation to the possible interactions with spatial scale, landform types, and data density. These results indicate that the accuracy of interpolation techniques for DEM generation should be tested not only in relation to landform types and data density but also to their applicability to multi-scales. (c) 2006 Elsevier B.V. All rights reserved.
Published: 2006
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36. Soil detachment and transport on field- and laboratory-scale interrill areas: erosion processes and the size-selectivity of eroded sediment

Author: David Favis-Mortlock, Y. Le Bissonnais, John Wainwright, Norbert Silvera, Olivier Planchon, O. Malam Issa, Groupe d'Étude sur les Géomatériaux et Environnements Naturels, Anthropiques et Archéologiques - EA 3795 (GEGENAA), Université de Reims Champagne-Ardenne (URCA)-SFR Condorcet, Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS)-Université de Reims Champagne-Ardenne (URCA)-Université de Picardie Jules Verne (UPJV)-Centre National de la Recherche Scientifique (CNRS)-Maison des Sciences Humaines de Champagne-Ardenne (MSH-URCA), Université de Reims Champagne-Ardenne (URCA)-Université de Reims Champagne-Ardenne (URCA), Labo BioMCo - INAPG, Institut de Recherche pour le Développement (IRD [Nouvelle-Calédonie]), Queen's University [Belfast] (QUB), Sols, usages des terres, dégradation, réhabilitation (SOLUTIONS), and Sheffield Centre for International Drylands Research, Department of Geography
Subjects: splash, 010504 meteorology & atmospheric sciences, SOIL CRUSTING, Geography, Planning and Development, interrill erosion, runoff, [SDV.SA.SDS]Life Sciences [q-bio]/Agricultural sciences/Soil study, INTERRILL EROSION, 01 natural sciences, WASH, Earth and Planetary Sciences (miscellaneous), soil crusting, RUNOFF, 0105 earth and related environmental sciences, Earth-Surface Processes, Hydrology, Splash, wash, sediment size distribution, Sediment, Crust, 04 agricultural and veterinary sciences, SEDIMENT SIZE DISTRIBUTION, SPLASH, Soil water, 040103 agronomy & agriculture, Erosion, Spatial ecology, 0401 agriculture, forestry, and fisheries, Environmental science, Surface runoff, Intensity (heat transfer)
Abstract: Field- and laboratory-scale rainfall simulation experiments were carried out in an investigation of the temporal variability of erosion processes on interrill areas, and the effects of such variation upon sediment size characteristics. Poorly aggregated sandy soils from the semiarid environment of Senegal, West Africa, were used on both a 40 m(2) field plot and a 0-25 m(2) laboratory plot; rainfall intensity for all experiments was 70 mm h(-1) with a duration of 1 to 2 hours. Time-series measurements were made of the quantity and the size distribution of eroded material: these permitted an estimate of the changing temporal balance between the main erosion processes (splash and wash). Results from both spatial scales showed a similar temporal pattern of runoff generation and sediment concentration. For both spatial scales, the dominant erosional process was detachment by raindrops; this resulted in a dynamic evolution of the soil surface under raindrop impact, with the rapid formation of a sieving crust followed by an erosion crust. However, a clear difference was observed between the two scales regarding the size of particles detached by both splash and wash. While all measured values were lower than the mean weight diameter (MWD) value of the original soil (mean 0(.)32 mm), demonstrating the size-selective nature of wash and splash processes, the MWD values of washed and splashed particles at the field scale ranged from 0(.)08 to 0(.)16 mm and from 0(.)12 to 0(.)30 mm respectively, whereas the MWD values of washed and splashed particles at the laboratory scale ranged from 0(.)13 to 0(.)29 mm and from 0(.)21 to 0(.)32 mm respectively. Thus only at the field scale were the soil particles detached by splash notably coarser than those transported by wash. This suggests a transport-limited erosion process at the field scale. Differences were also observed between the dynamics of the soil loss by wash at the two scales, since results showed wider scatter in the field compared to the laboratory experiments. This scatter is probably related to the change in soil surface characteristics due to the size-selectivity of the erosion processes at this spatial scale. Copyright (c) 2006 John Wiley and Sons, Ltd.
Published: 2006
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37. An automated salt-tracing gauge for flow-velocity measurement

Author: Raphael Gimenez, Olivier Planchon, David Favis-Mortlock, Norbert Silvera, Gerard Govers, Yves Le Bissonnais, John Wainwright, Laboratoire d'étude des Interactions Sol - Agrosystème - Hydrosystème (UMR LISAH), Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Centre international d'études supérieures en sciences agronomiques (Montpellier SupAgro)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro), Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro), Institut de Recherche pour le Développement (IRD), Institut de Recherche pour le Développement, Partenaires INRAE, Laboratory for Experimental Geomorphology, Queen's University [Belfast] (QUB), King‘s College London, Unité de Science du Sol, Institut National de la Recherche Agronomique (INRA), and Unité de recherche Science du Sol (USS)
Subjects: 010504 meteorology & atmospheric sciences, ACQUISITION DE DONNEES, [SDV]Life Sciences [q-bio], Geography, Planning and Development, PEDOLOGIE, 0207 environmental engineering, TRACING, Geometry, 02 engineering and technology, 01 natural sciences, Standard deviation, Earth and Planetary Sciences (miscellaneous), Calibration, MESURE, Acoustic Doppler velocimetry, INSTRUMENT DE MESURE, Diffusion (business), ECOULEMENT, 020701 environmental engineering, JAUGEAGE, VITESSE D'ECOULEMENT, 0105 earth and related environmental sciences, Earth-Surface Processes, Physics, Hydrology, Turbulence, FLOW VELOCITY, SOIL EROSION SALT, SEL DE TRACAGE, Supercritical flow, Open-channel flow, Flow velocity, [SDE]Environmental Sciences
Abstract: Correspondance: oliver.planchon@pgrignon.inra.fr; International audience; This article introduces the SVG (salt-velocity gauge), a novel automated technique for measuring flow velocity by means of salt tracing. SVG allows a high measuring rate (up to one every 2 seconds), short control section length (down to 10 cm), high accuracy (+/-1.5 cm s(-1)), and unbiased calculation of the mean velocity in experimental conditions with turbulent, supercritical How. A few cubic centimetres or saturated salt solution (NaCl) are injected into the flow at regular time intervals using a programmable solenoid valve. The tracer successively passes two conductivity probes placed a short distance downstream. The transformation of the signal between the two probes is modelled as a one-dimensional diffusion wave equation. Model calibration gives an estimation of the mean velocity and the diffusion for each salt plume. Two implementations of the SVG technique are described. The first was an outdoors simulated rainfall experiment in Senegal (conductivity probes at 40 cm apart, 8 Hz measurement rate, salt injections at 10 second intervals). Mean velocity was estimated to range between 0.1 and 0.3 m s(-1). The second was a laboratory-based flume experiment (conductivity probes at 10 cm apart, 32 Hz, salt injections at 2 second intervals). Another SVG with probes at 34 cm apart was used for comparison. An acoustic Doppler velocimeter (ADV) was also used to give an independent assessment of velocity. Using the 10 cm salt gauge, estimated mean velocity ranged from 0.6 to 0.9 m s(-1) with a standard deviation of 1.5 cm s(-1). Comparisons between ADV, 10 cm SVG and 34 cm SVG were consistent and demonstrated that the salt-tracing results were unbiased and independent of distance between probes. Most peaks were modelled with (2) > 90 per cent. The SVG technology offers an alternative to the dye-tracing technique, which has been severely criticized in the literature because of the wide interval of recommended values for the correction factor alpha to be applied to the timings. This article demonstrates that a fixed value of alpha is inappropriate, since the correction factor varies with velocity, diffusion and the length of the control section
Published: 2005
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38. Longitudinal velocity patterns and bed morphology interaction in a rill

Author: Rafael Giménez, Olivier Planchon, Norbert Silvera, and Gerard Govers
Subjects: Bedform, Hydraulics, Geography, Planning and Development, law.invention, symbols.namesake, law, Earth and Planetary Sciences (miscellaneous), Froude number, HYDRAULIQUE, Acoustic Doppler velocimetry, PROFONDEUR, Geomorphology, Hydraulic jump, Earth-Surface Processes, FLUX HYDRIQUE, geography, geography.geographical_feature_category, VITESSE, CONFIGURATION DU LIT, Elevation, TOPOGRAPHIE, Rill, APPAREIL DE MESURE, RUISSEAU, COURS D'EAU, Erosion, symbols, HYDRODYNAMIQUE, PENTE, EROSION HYDRIQUE, COURANTOMETRIE, Geology
Abstract: Present-day understanding of rill dynamics is hampered by a lack of detailed data on velocity distributions in rills. The latter are difﬁcult to collect with traditional techniques due to the very low water depths and the relatively high ﬂow velocities in rills. The objectives of this paper were to investigate the feasibility of miniaturized acoustic Doppler velocimeter (mADV) measurements in rill ﬂow and to explore longitudinal variations in ﬂow velocities and their relationship with rill bed morphology. Detailed data on longitudinal ﬂow velocity were required to achieve these objectives. A 1·8 m long rill was formed freely in a ﬂume at 5° slope and 0·001 m3 s−1 discharge. Rill topography was characterized by an alternation of steps and pools. The ﬂume surface was then ﬁxed to preserve rill roughness. A topographical scanning of the entire ﬂume surface was made. Velocity was measured with a mADV along the rill, and at different depths. Flow depth in a longitudinal direction was also measured using an elevation gauge. A strong relationship exists between rill topography and ﬂow hydraulics. Over steps, ﬂow was unidirectional and rapidly accelerating until a threshold Froude number (Fn) value between 1·3 and 1·7 was reached and a hydraulic jump occurred leading to the formation of a pool. In the pool, the ﬂow pattern was multidirectional and complex. The ﬂow was subcritical when leaving the pool and accelerated over the next step until the threshold Froude number value was again reached. Energy loss in the rill was concentrated in the pools, mainly due to the action of a hydraulic jump. This mechanism of energy dissipation appeared to be an essential factor in rill formation and bedform evolution. Copyright © 2004 John Wiley & Sons, Ltd.
Published: 2004

39. Raindrop erosion of tillage induced microrelief : possible use of the diffusion equation

Author: Norbert Silvera, Jean-Marc Lapetite, Michel Esteves, and Olivier Planchon
Subjects: Diffusion equation, Correlation coefficient, Compaction, Soil Science, MICRORELIEF, Soil science, TRAVAIL DU SOL, ECOULEMENT DE SURFACE, ETAT DE SURFACE DU SOL, MODELISATION, Tillage, COMPACITE, STOCKAGE, EAU, Erosion, EQUATIN DE DIFFUSION, Precipitation, EROSION HYDRIQUE, Diffusion (business), SIMULATION DE PLUIE, Surface runoff, Agronomy and Crop Science, Earth-Surface Processes, Mathematics, ANALYSE NUMERIQUE
Abstract: The purpose of this paper is to evaluate the possibility of using the diffusion equation for raindrop erosion modelling. We wanted in particular to know if such a model could provide accurate interpolations of microrelief between two known dates. In a theoretical section, we show that the assumption that soil particles follow parabolic trajectories when splashed by raindrop impacts leads to a diffusion equation. This equation suggests a linear relation between Dz, the variation of height between two dates, and the Laplacianr 2 z (r 2 za@ 2 z/@x 2 a@ 2 z/@y 2 ). This relation is confirmed by data from a simulated rainfall experiment carried out in the sandy soils of the Senegalese groundnut belt. Four square plots of side 4 m each were used. They were hoed with a traditional horse-drawn three-tined hoe. Three rains of 70 mm h ˇ1 lasting 30 min each were applied. An automated relief meter designed and constructed by the authors was used to measure the distribution of heights for every 5 cm before the first rain, and after the first and the third rains. The mean correlation coefficient of the model was 62% for the first rain and 46% for the next two rains. Besides raindrop erosion, compaction occurred during the first rain. Adding a crude description of compaction enhanced the mean of the correlation coefficients of the model up to 70% for the first rain. Furthermore, the coefficient of variation of the four adjusted total diffusion lessens from 10 to 6%. The simulated surfaces were smoother than the real ones, which was an expected result, but the surface storage capacity was overestimated. The latter result illustrates the role of runoff in shaping the flow paths it follows and, consequently, in lessening the surface storage capacity. The main conclusion is that the diffusion equation provides a promising frame for further development of models simulating microrelief evolution during rainfall. Another conclusion is that these models should integrate existing routines for runoff erosion at small scale in order to simulate surfaces with realistic hydraulic properties. # 2000 Published by Elsevier Science B.V.
Published: 2000

40. The 'EMIRE' large rainfall simulator : design and field testing

Author: Olivier Planchon, Patrice Cadet, Norbert Silvera, Michel Esteves, and Jean Marc Lapetite
Subjects: Hydrology, Square tiling, Field data, Geography, Planning and Development, Soil science, Repeatability, Water pressure, Soil gradation, APPAREIL DE MESURE, Infiltration (hydrology), Rainfall simulator, VARIATION SPATIALE, Earth and Planetary Sciences (miscellaneous), INTENSITE, Spatial variability, EROSION HYDRIQUE, SIMULATION DE PLUIE, ECOULEMENT, Earth-Surface Processes, Mathematics
Abstract: Arainfallsimulatorfor510 mplotswasdesignedandtestedwithintheEMIRE(EtudeetModelisationdel'Infiltration,du Ruissellement et de l'Erosion) program. The simulator is intended to be used in the field and to reproduce natural tropical rainstorms.Thesimulatoriscomposedoffixedstandpipes.Thenozzle(SprayingSystemsCo.1H106SQ)mountedonthe topof the pipes sprays square areas. Ata water pressure of 4118 kPa themean dropdiameter is 24 mmand the calculated kinetic energy235Jm ˇ2 mm ˇ1 . The pipes are located at the corners of a 55 55 m square grid. Therainfall intensity is constant (65 mm h ˇ1 ) and spatially uniform (Christiansen's coefficient of uniformity is 78 to 92 per cent) over the plot. Repeatability of application rate and spatial variability of rainfall intensities were tested by analysing (1) variations in intensityfordifferentexperimentsonthesameplot,and(2)variationsinintensitybetweendifferentplots.Thestudyisbased ondatacollectedduringninefieldrainfallsimulationexperiments.Threereplicationsofthesamerainwereappliedonthree 50 m 2 plots. The results show good performance in all cases. The values of the mean rainfall intensities and coefficient of uniformity obtained from field data agreed with the laboratory values. The performance of this simulator is comparable to others described in the literature. Copyright # 2000 John Wiley & Sons, Ltd.
Published: 2000

41. An automated salt-tracing gauge for flow-velocity measurement.

Author: Olivier Planchon, Norbert Silvera, Raphael Gimenez, David Favis-Mortlock, John Wainwright, Yves Le Bissonnais, and Gerard Govers
Subjects: CALIBRATION, PHYSICAL measurements, STANDARDIZATION, INDUSTRIAL engineering
Abstract: This article introduces the SVG (salt-velocity gauge), a novel automated technique for measuring flow velocity by means of salt tracing. SVG allows a high measuring rate (up to one every 2 seconds), short control section length (down to 10 cm), high accuracy (+[sol ]-15 cm s-1), and unbiased calculation of the mean velocity in experimental conditions with turbulent, supercritical flow.A few cubic centimetres of saturated salt solution (NaCl) are injected into the flow at regular time intervals using a programmable solenoid valve. The tracer successively passes two conductivity probes placed a short distance downstream. The transformation of the signal between the two probes is modelled as a one-dimensional diffusion wave equation. Model calibration gives an estimation of the mean velocity and the diffusion for each salt plume.Two implementations of the SVG technique are described. The first was an outdoors simulated rainfall experiment in Senegal (conductivity probes at 40 cm apart, 8 Hz measurement rate, salt injections at 10 second intervals). Mean velocity was estimated to range between 01 and 03 m s-1. The second was a laboratory-based flume experiment (conductivity probes at 10 cm apart, 32 Hz, salt injections at 2 second intervals). Another SVG with probes at 34 cm apart was used for comparison. An acoustic Doppler velocimeter (ADV) was also used to give an independent assessment of velocity. Using the 10 cm salt gauge, estimated mean velocity ranged from 06 to 09 m s-1 with a standard deviation of 15 cm s-1. Comparisons between ADV, 10 cm SVG and 34 cm SVG were consistent and demonstrated that the salt-tracing results were unbiased and independent of distance between probes. Most peaks were modelled with r2> 90 per cent.The SVG technology offers an alternative to the dye-tracing technique, which has been severely criticized in the literature because of the wide interval of recommended values for the correction factor a to be applied to the timings. This article demonstrates that a fixed value of a is inappropriate, since the correction factor varies with velocity, diffusion and the length of the control section. Copyright 2005 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]
Published: 2005
Full Text: View/download PDF

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