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Shrink-swell soils, such as those in a Mediterranean climate regime, can cause changes in terms of hydrological and erosive responses because of the changing soil water storage conditions. Only a limited number of long-term studies have focused on the impacts on both hydrological and erosive responses and their interactions in an agricultural environment. In this context, this study aims to document the dynamics of cracks, runoff and soil erosion within a small Mediterranean cultivated catchment and to quantify the influence of crack processes on the water and sediment supplied to a reservoir located at the catchment outlet using water and sediment measurements at a cultivated field outlet as baseline. Detailed monitoring of the presence of topsoil cracks was conducted within the Kamech catchment (ORE OMERE, Tunisia), and runoff and suspended sediment loads were continuously measured over a long period of time (2005-2012) at the outlets of a field (1.32 ha) and a catchment (263 ha). Analysis of the data showed that topsoil cracks were open approximately half of the year and that the rainfall regime and water table level conditions locally control the seasonal cracking dynamics. Topsoil cracks appeared to seriously affect the generation of runoff and sediment concentrations and, consequently, sediment yields, with similar dynamics observed at the field and catchment outlets. A similar time lag in the seasonality between water and sediment delivery was observed at these two scales: although the runoff rates were globally low during the presence of topsoil cracks, most sediment transport occurred during this period associated with very high sediment concentrations. This study underlines the importance of a good prediction of runoff during the presence of cracks for reservoir siltation considerations. In this context, the prediction of cracking effects on runoff and soil erosion is a key factor for the development of effective soil and water management strategies and downstream reservoir preservation. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Reservoir siltation because of water erosion is an important environmental issue in Mediterranean countries where storage of clear surface water is crucial for their economic and agricultural development. The high density of gully systems observed in Mediterranean regions raises the question of their contribution to reservoir siltation. In this context, this study quantified the absolute and relative contributions of rill/interrill and gully/channel erosion in sediment accumulation at the outlet of small Tunisian catchments (0·1-10 km2) during the last 15 years (1995-2010). To this end, a fingerprinting method based on measurements of caesium-137 and total organic carbon combined with long-term field monitoring of catchment sediment yield was applied to five catchments in order to cover the diversity of environmental conditions found along the Tunisian Ridge and in the Cape Bon region. Results showed the very large variability of erosion processes among the selected catchments, with rill/interrill erosion contributions to sediment accumulated in outlet reservoirs ranging from 20 to 80%. Overall, rill/interrill erosion was the dominant process controlling reservoir siltation in three catchments whereas gully/channel erosion dominated in the other two catchments. We identified the presence of marly gypsum substrates and the proportion of catchment surface covered by soil management/conservation measures as the main drivers of erosion process variability at the catchment scale. These results provided a sound basis to propose guidelines for erosion mitigation in these Mediterranean environments and suggested to apply models simulating both rill/interrill and gully/channel erosion in catchments of the region. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Soil erosion surveys and modeling approaches often rely on datasets collected from small experimental plots or fields. Therefore, one important issue is to assess to what extent reference data collected on small areas can be affected by soil tillage practices and extrapolated to larger areas. The objectives of this paper are to discuss: (i) the impact of superficial tillage on the erosion rates at field scale and (ii) the impact of the scale on the erosion rates for areas ranging from small fields to 1km2 catchments. We analyzed a dataset of 18 rainfall events including runoff and erosion data from fields of approximately 1200m2 and 3200m2 consisting of vineyards with two contrasting weeding practices – either superficial tillage or no-tillage with chemical weeding – and from the outlet of a 0.91km2 catchment that was 70% vineyard. Results showed that superficial tillage significantly reduced (4.5 times) soil losses as compared to no-tillage, with a large event-to-event variability. Considering the natural conditions studied by the authors, no-tillage with chemical weeding is not recommended for the study area. Erosion rates observed at catchment scale were significantly lower than those observed at the scale of individual fields. This trend, which has already been observed by many researchers, confirms that catchment soil loss cannot be estimated by the sum of individual field soil losses. In this context, the scaling transition between the field and the 1km2 catchment can be analyzed in terms of the spatial variability of soil management and connectivity between the sediment-producing and deposition areas. [Copyright &y& Elsevier]

Various interactions, particularly those existing between the rainfall intensity, the slope gradient, the slope length, and the tillage supposedly can affect the runoff features for interrill erosion. Despite numerous studies, their effect on runoff production and pathways and the resulting soil losses have seldom been analyzed. This is especially true under field and tillage conditions. This study investigated the effect of rainfall intensity, slope length, and gradient on runoff amount and pathways for interrill erosion in tilled fields. Runoff features and soil losses were evaluated on bounded plots of 1- and 5-m length located on 4 to 8% slope gradients, and under natural and simulated rainfalls with intensities ranging from 1.5 to 30 mm h[sup -1]. Runoff coefficients (R) ranged from 34 to 98% whereas sediment concentrations (SC) varied from 2.9 to 49 g l[sup -1]. The runoff coefficient was affected by all three factors: rainfall intensity (r = 0.48; P < 0.0001), slope gradient (r = 0.51; P < 0.0001) and slope length (r = 0.29; P = 0.02); whereas SC was correlated with only rainfall intensity (r = 0.48; P < 0.0001) and slope length (r = 0.44; P = 0.0004). The runoff coefficient and SC ratios between 1- and 5-m long plots were systematically greater for the intermediate rainfall intensity. Runoff features mainly affected by tillage implements may explain higher interrill erosion at longer and steeper slopes. Lower differences between 1- and 5-m plots at high rainfall intensity may reflect greater ponded runoff absorbing raindrop kinetic energy and lowering detachment and transport processes. Finally, the effects of rainfall intensity, slope length, and gradient and tillage are discussed in respect of possible erosion processes operating in the experiments. [ABSTRACT FROM AUTHOR]

The Common Agricultural Policy (CAP) of the European Union, technological developments, and commercial pressures to maximise returns and minimise costs, have given rise to a marked intensification of agriculture, particularly in the last 30 years. This highly intensified agriculture has resulted in environmental problems such as erosion. More recently, the CAP reform has introduced agri-environmental measures as a means of combating soil erosion. However, even though the 1992 CAP reform was meant to contribute to overall grassland stabilisation, recent studies point to continued agronomic pressures to plough up grassland. This paper presents a brief synthesis of crop trends and environmental impacts on erosion in Upper Normandy, France. Our analysis is based on data from the French agricultural censuses and on some remote sensing results from the FLOODGEN European project. We also used the simulation capacity of the runoff and erosion STREAM model to test the consequences of grassland decrease in agricultural catchments and to show the efficiency of some agri-environmental measures. Results show that Upper Normandy has lost 200,000 ha of permanent grassland between 1970 and 2000. A simulation performed with the STREAM model shows that the ploughing up of 17% of permanent grassland leads to a sharp rise both in runoff volume (>75%) and soil loss (>85%) within a catchment basin. [Copyright &y& Elsevier]

Wildfire is known to create the pre-conditions leading to accelerated soil erosion. Unfortunately, its occurrence is expected to increase with climate change. The objective of this study was to assess the impacts of fire on runoff and soil erosion in a context of global change, and to evaluate the effectiveness of mulching as a post-fire erosion mitigation measure. For this, the long-term soil erosion model LandSoil was calibrated for a Mediterranean catchment in north-central Portugal that burnt in 2011. LandSoil was then applied for a 20-year period to quantify the separate and combined hydrological and erosion impacts of fire frequency and of post-fire mulching using four plausible site-specific land use and management scenarios (S1. business-as-usual, S2. market-oriented, S3. environmental protection and S4. sustainable trade-off) and an intermediate climate change scenario Representative Concentration Pathway (RCP) 4.5 by 2050. The obtained results showed that: (i) fire had a reduced impact on runoff generation in the studied catchment (<5%) but a marked impact on sediment yield (SY) by about 30%; (ii) eucalypt intensification combined with climate change and fires can increase SY by threefold and (iii) post-fire mulching, combined with riparian vegetation maintenance/restoration and reduced tillage at the landscape level, was highly effective to mitigate soil erosion under global change and associated, increased fire frequency (up to 50% reduction). This study shows how field monitoring data can be combined with numerical erosion modeling to segregate the prominent processes occurring in post forest fire conditions and find the best management pathways to meet international goals on achieving land degradation neutrality (LDN). [ABSTRACT FROM AUTHOR]

Abstract: Erosion and deposition rates were quantified in a vineyard context (Languedoc, France) using a method based on vine-stock bio-markers. The within-field spatial structure of erosion (Field Erosive State) was described based on maps of “unearthing” height of vine-stock. The factors affecting variability of soil erosion (slope gradient, slope length, soil type, and field boundaries characteristics) were analysed in relation to quantitative and spatial erosion data. When this method was applied to a sample of 49 fields, the intensity of erosion in the study area (mean erosion rate=10.5t ha− 1 year− 1) showed a high variability between fields. The Field Erosive States (FES) were classified into five categories based on the intensity and spatial structure of the erosion, such as uniform erosion of the field, transfer of sediments from upslope to downslope regions and concentrated erosion on rills. This study highlights the influence of the connectivity between fields on erosion intensity and variability. [ABSTRACT FROM AUTHOR]

Abstract Soil erosion is the primary process driving land degradation. Using multiple scales of management to minimize soil erosion is crucial to achieve land degradation neutrality targets within the Sustainable Development Goals agenda. Land management (LM) influences both on-site and off-site erosion on the event-scale and over the long-term. However, each LM differs in effectiveness depending on the temporal scale considered. In order to understand how LM effects internal and external catchment dynamics, we apply LandSoil, a physically based landscape evolution model, to evaluate 7 LM scenarios over long- (30 years) and short-terms (event scale). LM scenarios included changes in land use and/or landscape structure. Under current LM, mean surface soil erosion was ∼0.69 ± 39·10−3 m over 30 years. In contrast, a single extreme event (435 mm/24 h) in January resulted in ∼0.62 ± 3·10−3 m loss and ∼0.04 ± 2·10−3 m if it occurred in October. Heterogeneous patterns of erosion and deposition developed after 30 years, whereas extreme events dominantly showed soil loss and high catchment connectivity. Effectiveness of LM in erosion mitigation and sediment trapping differed according to temporal and spatial scales for each scenario. We concluded that multiple temporal and spatial scales must be incorporated in order to adaptively manage land degradation and meet neutrality targets. Highlights • Internal and external catchment dynamics differ for long-term and extreme events. • Land degradation neutrality requires management efficiency for both time scales. • Combined land use, landscape structure and connectivity management is needed. • LandSoil model enables comparison of management efficiency on differing time scales. [ABSTRACT FROM AUTHOR]

Soil aggregate stability is a key factor in soil resistance to water erosion, which is a threat to soils in a large part of northern Tunisia. The analysis of the spatial variability of soil aggregate stability provides both agronomic and environmentally useful information. However, extensive measurements of soil aggregate stability remain tedious and expensive. This study explores two different approaches as alternative to measurements of soil aggregate stability. One approach estimated aggregate stability via laboratory measurements of soil elementary properties using multiple linear regressions known as pedotransfer functions. The second approach, which is methodologically innovating, was based on the geological pattern as a proxy for aggregate stability using regression-kriging analysis. A set of 113 soil samples from an 800 km 2 agricultural region that included the Lebna watershed (Cap Bon, Tunisia) were collected from the soil surface layer (0–10 cm depth). Samples were analyzed for elementary properties (i.e., soil texture, total carbon and nitrogen, iron, CaCO 3 , salinity, CEC and pH) and for soil aggregate stability according to the normalized method (ISO/DIS 10930, 2012), which considers three indexes (MWD) calculated for three contrasted wetting conditions and disruptive energies. Most soils in the study area were non-salted with an alkaline pH and relatively low organic carbon content. Of the soils, 35% were clay soils, and 55% had a balanced soil texture. The average of the three soil aggregate stability indexes (MWD mean ) ranged from 0.38 to 2.80 mm, and this property showed large variability from instable soils to very stable ones. Analysis of pedotransfer functions determined that the best predictor variables for soil aggregate stability were silt, organic matter and iron. Geostatistical analyses at the regional scale showed spatially structured soil aggregate stability (variograms with sills reaching a 5 km distance). Using geological information as ancillary data, the prediction of soil aggregate stability with regression-kriging was similar to that of pedotransfer functions. A regression-kriged map of soil aggregate stability associated with a map of prediction uncertainties was developed. The resulting maps and methods of this study can be useful in the development of management options that minimize water erosion risks in the studied area. [ABSTRACT FROM AUTHOR]

Soil aggregates are organomineral associations with a fundamental importance for soil structure and function. Litter from vegetation alters aggregate formation and stability, and polyphenols such as tannins found in leaves, roots and wood play an important role in soil biogeochemical and biological processes. However, the effect of tannins on soil physical properties remains largely unexplored. We hypothesized that tannins influence aggregate stability through their ability to (i) complex proteins in the soil and (ii) perturb the gelling property of root mucilage. Therefore, Mediterranean soil aggregates were incubated with condensed tannins, either as a pure substrate or in combination with a standard protein (bovine serum albumin, BSA) and with a model root mucilage polysaccharide (polygalacturonic acid, PGA) able to form gel-like structures with divalent cations (notably Ca 2+ ) widely present in Mediterranean calcareous soils. The changes in aggregate stability were monitored under controlled conditions, immediately after the addition of tannins, after 2 weeks, 3 and 6 months of incubation. Tannins added alone did not yield a significant effect on aggregate stability. However, modulatory effects were found when combinations of treatments occurred. Tannins positively modulated the stabilizing effect of the BSA, giving credit to our hypothesis on the stabilizing role of the tannin-protein complex forming macromolecules, thus enforcing soil particle cohesion within aggregates. However, tannins negatively altered the stabilizing effect of PGA, suggesting that the expected perturbation of the PGA gelation occurred, with detrimental consequences for aggregate stability. Over time, tannins maintained the effect of BSA, suggesting a protective effect of tannins, possibly linked to their ability to slow down the degradation of nitrogen compounds through protein binding. Overall, we showed that tannins reacted with other organic compounds resulting in specific effects on physical soil properties, thus demonstrating that tannins in soils play a role beyond their effects on biogeochemical aspects. [ABSTRACT FROM AUTHOR]

The objective of this study was to simulate the evolution of soil erosion in a semi-arid mountainous watershed (225 km 2 , High Atlas Mountains, Morocco) under different scenarios of climate and land use change to the end of 21st century. Erosion plots monitored over four years showed spatially contrasted results. Most of the soils produced from 0.015 to 2.5 t ha −1 y −1 , whereas badlands produced 350 t ha −1 y −1 . The average sediment yield measured at the outlet during the same period was approximately 4 t ha −1 y −1 . The STREAM distributed erosion model was parameterized using these field measurements (infiltration rates and runoff sediment concentrations). The results showed an overall agreement between the modelled and measured annual cumulative sediment yields. Simulations of the ARPEGE meteorological model were used for the 1960–1990 and 2070–2100 periods. The changes between these two periods were downscaled using three different methods, decreasing annual precipitations by 10–14%, although with more rainfall in summer and fall. Climate change alone increased sediment yield by 4.7–10.1%. However, simulations showed that land use changes might potentially induce much larger changes in erosion (up to 250%), approximately proportional to the evolution of the extension of badlands. [ABSTRACT FROM AUTHOR]

Global climate and land use changes could strongly affect soil erosion and the capability of soils to sustain agriculture and in turn impact regional or global food security. The objective of our study was to develop a method to assess soil sustainability to erosion under changes in land use and climate. The method was applied in a typical mixed Mediterranean landscape in a wine-growing watershed (75 km 2 ) within the Languedoc region (La Peyne, France) for two periods: a first period with the current climate and land use and a second period with the climate and land use scenarios at the end of the twenty-first century. The Intergovernmental Panel on Climate Change A1B future rainfall scenarios from the Météo France General circulation model was coupled with four contrasting land use change scenarios that were designed using a spatially-explicit land use change model. Mean annual erosion rate was estimated with an expert-based soil erosion model. Soil life expectancy was assessed using soil depth. Soil erosion rate and soil life expectancy were combined into a sustainability index. The median simulated soil erosion rate for the current period was 3.5 t/ha/year and the soil life expectancy was 273 years, showing a low sustainability of soils. For the future period with the same land use distribution, the median simulated soil erosion rate was 4.2 t/ha/year and the soil life expectancy was 249 years. The results show that soil erosion rate and soil life expectancy are more sensitive to changes in land use than to changes in precipitation. Among the scenarios tested, institution of a mandatory grass cover in vineyards seems to be an efficient means of significantly improving soil sustainability, both in terms of decreased soil erosion rates and increased soil life expectancies. [ABSTRACT FROM AUTHOR]

Abstract: Inappropriate agricultural land management practices cause irreversible soil losses in many parts of Europe. Soil degradation is predicted to increase in the next future as an effect of climate and cropping system changes. The most concerned areas are expected to be those already severely affected by erosion, as is the whole of the Mediterranean. Medium-term soil erosion models could be useful tools to analyse, understand and simulate complex interactions between geomorphic processes and human pressures for better assessment of medium-term soil redistributions associated with land use and landscape design change. The aim of this study was to compare the effects of various agricultural land uses and landscape design strategies on water and tillage erosion. The first step was to develop land use and landscape design scenarios of an agricultural Mediterranean landscape. Then, all of the scenarios were compared in terms of the soil redistribution using the LandSoil model. The results indicate that potential soil conservation associated with the adoption of sustainable land uses surpasses the potential conservation associated with certain landscape design. A detailed analysis of within-landscape soil redistributions suggests that land use is a major factor controlling sediment production, whereas landscape design is a major factor controlling hillslope connectivity. [Copyright &y& Elsevier]

Abstract: The modeling of soil erosion by water supposes an accurate and thorough understanding of the hydrology. Thus, it is critical to have a good delineation of the surface flow path. The flow network data are critical for important uses such as flood forecasting and watershed management. Geographic Information System (GIS) functions are able to compute a flow network directly from the digital elevation models. Because the flow directions are only based on the topography, the other factors controlling the flow directions are overlooked. In the agricultural areas, work such as tillage can have a large impact on the flow direction. We propose a 5-step procedure to account for such man-made features. The use of this procedure clearly improves the quality of the computed flow network. This procedure has been successfully implemented in a GIS and improves the prediction of surface flow and therefore improves water erosion modeling at the watershed scale. [Copyright &y& Elsevier]

Abstract: Soil erosion leads to important environmental problems (e.g. muddy floods, reservoir sedimentation) in cultivated areas of the European loess belt. This study aimed to determine the impact of rainfall seasonality and land use change on soil erosion over the last 40 years in a 94-ha cultivated catchment of Normandy (France). To this end, scenarios representative of the different land use conditions were simulated using the STREAM expert-based erosion model. A 13 years long sequence of rainfall events was run with this model. Results showed that erosion increased dramatically after land consolidation (+168% on average). Interannual variability of erosion is important. After land consolidation, 79% of erosion was observed in summer and autumn, even though these seasons only accounted for 58% of annual rainfall kinetic energy. The bulk of erosion was hence produced by a few intense thunderstorms during this period. Thunderstorms correspond to 5% of rainfall events and to 15% of the total rainfall depth, but they generate 51% of total annual erosion after land consolidation (and up to 57% of erosion before land consolidation). Confrontation of the STREAM model outputs with the erosion rates modelled based on Cs-137 measurements suggested that soil redistribution within the catchment was very high but that sediment exports from the catchment remained limited (sediment delivery ratio between 1% and 10%). Local erosion rates derived from Cs-137 measurements showed an important and organised spatial variability, but erosion rates integrated over larger areas remained in the same order of magnitude as those simulated by the STREAM model or were slightly higher. Water erosion would hence not be the only process generating erosion within this catchment. In this context, our results show that tillage erosion cannot be neglected to calculate the sediment budget over several decades. [Copyright &y& Elsevier]

Abstract: During the last decades, the European loess belt has been confronted with a significant increase in environmental problems due to erosion on agricultural land. Spatially distributed runoff and erosion models operating at the catchment scale are therefore needed to evaluate the impact of potential mitigation measures. Expert-based models offer an alternative solution to process-based and empirical models, but their decision rules are only valid for the local conditions for which they have been derived. The STREAM model, which was developed in Normandy (France), has been applied in two Belgian catchments having a similar soil texture, as well as in a catchment of southern France differing by soil, land use and climate characteristics. The performance of hydrological models can be assessed for instance by calculating the Nash–Sutcliffe efficiency criterion (E NS). When applied to Belgium, the model results are satisfactory to good after an adaptation of the decision rules (0.90< E NS <0.93 for runoff predictions and 0.85< E NS <0.89 for erosion predictions). Given the important environmental differences between Normandy and southern France, the model rules were also adapted for application in the latter environment. Unfortunately, the quality of runoff predictions was insufficient to simulate erosion in southern France. In conclusion, STREAM is a reliable model providing satisfactory runoff and erosion predictions in the regions where hortonian overland flow dominates. Nevertheless, an adaptation of decision rules based on local multi-scale (plot, field, catchment) data is needed, before running the model. STREAM can then serve as a decision support tool to design for instance flood control measures. [Copyright &y& Elsevier]