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Terraces and lynchets are ubiquitous worldwide and can provide increasingly important Ecosystem Services (ESs), which may be able to mitigate aspects of climate change. They are also a major cause of non-linearity between climate and erosion rates in agricultural systems as noted from alluvial and colluvial studies. New research in the ‘critical zone’ has shown that we must now treat soil production as an ecologically sensitive variable with implications for soil carbon sequestration. In this review and synthesis paper we present a modified classification of agricultural terraces, review the theoretical background of both terraces and lynchets, and show how new techniques are transforming the study of these widespread and often ancient anthropogenic landforms. The problems of dating terraces and the time-consuming nature of costly surveys have held back the geomorphological and geoarchaeological study of terraces until now. The suite of techniques now available, and reviewed here, includes Digital Elevation Models (DEMs) - Structure from Motion (SfM) photogrammetry, Airborne and Terrestrial Laser Scanning (ALS-TLS); optically stimulated luminescence (OSL and pOSL), portable X-ray fluorescence (pXRF), Fourier-transform infra-red analysis (FTIR), phytoliths from plants, and potentially environmental DNA. Three process-related geomorphological questions arise from using this suite of methods; a) can they provide both a chronology of formation and use history, b) can we identify the sources of all the soil components? c) Can terrace soil formation and ecosystem services be modelled at the slope to catchment scale? The answers to these questions can also inform the management of the large areas of abandoned and under-used terraces that are resulting from both the economics of farming and rural population changes. Where possible, examples are drawn from a recently started ERC project (TerrACE; ERC-2018-2023; https://www.terrace.no/) that is working at over 15 sites in Eur

Le sujet de cette thèse évalue la possibilité de délimiter des terroirs géochimiques sur le territoire de l’actuelle Belgique, à partir de l’étude géochimique des formations argileuses. Ce questionnement trouve son origine dans la problématique de la détermination de provenance des céramiques communes gallo-romaines. La comparaison des compositions géochimiques d’argiles sensu lato et de céramiques communes provenant de sites de consommation mettrait en évidence les plus fortes ressemblances, ce qui désignerait la région d’origine : un des terroirs géochimiques. Pour démêler la possibilité de délimiter des terroirs géochimiques, les trois autres problématiques suivantes ont dû être résolues. D’une part, distinguer les différentes formations argileuses à potentiel céramique (utilisation au tour) entre elles sur base de leur composition géochimique. Ceci a pu être démontré par l’analyse des compositions géochimiques pour sept formations argileuses dont le potentiel céramiques avait été évalué auparavant sur un ensemble de quinze formations échantillonnées ; Ensuite, identifier la matière première de groupes de référence céramique de sites de production, ce qui n’avait, jusqu’à ce jour, pu être fait. Trois ateliers de potiers de la Cité des Tongres (Amay, Liberchies et Tirlemont), fabriquant de la céramique commune et situés dans des contextes géologiques différents, ont été choisis pour faire l’objet d’une caractérisation archéométrique poussée de leur production. Les résultats montrent que dans chaque officine il y a eu mélange de deux types d’argile pour la fabrication des pâtes : une des argiles utilisées est à chaque fois une argile de type smectitique, plutôt riche en fer (Fe2O3≥ 3 %) et l’autre argile est une argile de type kaolinitique, assez pauvre en fer (Fe2O3≤ 3 %). Enfin, distinguer les productions d'ateliers exploitant des formations argileuses différentes. Ceci a pu être démontré sur la base de l’étude des productions des trois officines étudiées. Les ré, (DOCSC04) -- FUNDP, 2014

Weathered heterogeneous siliciclastic rocks are ubiquitous in the Walloon Region. This study first aims to characterize and secondly to map the weathered rocks, the characterization remaining an essential step of the mapping work. Firstly the characterization was performed on the Ardennian Allochthonous (Ardenne Anticlinorium and Dinant Synclinorium) and the Brabant Parautochthonous (Brabant Massif). Based on macroscopic observations, classification of weathering degrees of alterites is proposed. The mineralogy (XRD, thin section) and the geochemistry (major elements, trace elements, REE) of the studied sites are quite consistent with these categories. The evolutions of clay parageneses and Vogt's weathering index (1927) provide representative results of the weathering degree at the regional scale. The dated alterites do confirm the presence of five weathering periods in the Walloon Region: Permian-Triassic, Early Cretaceous, "middle" Cretaceous, Paleocene-Eocene and Miocene. Within these periods, the weathering is induced during favorable phases. A chronological model of saprolitisation is proposed for the Walloon Region: a relationship between weathering phases, climate and relative sea-level changes is suggested. Secondly the knowledge acquired by the characterization of the weathering profiles in the Walloon Region facilitates the mapping of the weathered rocks in the Haute-Lesse area. The tools and methods tested in this work show several advantages and disadvantages for the mapping of weathered siliciclastic rocks. Those selected allow a distinction between the different types of alterites. A methodology based on the airborne radiometry to map the weathered heterogeneous siliciclastic rocks at the regional scale is developed. Confirming the uplift of the Ardennes, the airborne radiometry is a suitable tool for geomorphology. The mapping of weathered rocks in the Walloon Region would be useful through a field survey on topographic maps at the 1/10.000 scale. Th, Les roches silicoclastiques hétérogènes altérées par des fluides météoriques sont omniprésentes en Région Wallonne. Cette étude vise, dans un premier temps, à les caractériser et, dans un second temps, à les cartographier ; la caractérisation détaillée demeurant une étape indispensable à la cartographie. Dans un premier temps, les roches altérées (altérites) de l'Allochtone Ardennais (Anticlinorium de l'Ardenne et Synclinorium de Dinant) et du Parautochtone Brabançon (Massif du Brabant) sont caractérisées. Sur base d'observations macroscopiques, une classification du degré d'altération des altérites est proposée. La minéralogie (DRX, lames minces) et la géochimie (éléments majeurs, en traces, Terres rares) des sites étudiés sont assez cohérentes avec ces différentes catégories. Les évolutions des paragenèses argileuses et de l'indice d'altération V de Vogt (1927) traduisent le degré d'altération à l'échelle régionale. Les altérites datées confirment la présence de cinq périodes propices à l'altération météorique en Région Wallonne : Permo-Trias, Crétacé Inférieur, Crétacé "moyen", Paléocène-Eocène et Miocène. Au sein de ces périodes, l'altération météorique est activée durant des phases particulièrement favorables. Un modèle chronologique de saprolitisation est proposé à l'échelle de la Région Wallonne : une relation entre les phases d'altération, le climat et les variations relatives du niveau marin est suggérée. Dans un second temps, les connaissances acquises par la caractérisation de l'altération météorique en Région Wallonne facilitent la cartographie des roches altérées dans la région de la Haute-Lesse. Les outils et méthodes testés dans ce travail montrent plusieurs avantages et inconvénients pour la cartographie des roches altérées silicoclastiques hétérogènes. Ceux qui sont retenus autorisent une distinction entre les différentes catégories d'altérites. Une méthodologie basée sur la radiométrie aéroportée permettant de cartographier les roches silicoclastiq, (DOCSC04) -- FUNDP, 2012

The basin of Moulouya Oued is a region where mining industry has been developed early in the 20th century. As a consequence, residues generated from past mining activities over the years have been dumped as piles of tailings. Zaïda is one of the most affected region in this basin because of lead mine exploitation for long time. The aim of this study is to determine the amount of trace elements and the contamination of the river sediments. Analysis of collected samples has been achieved using the prompt gamma activation analysis method. The samples, in form of powders, were enclosed in Teflon sheets. The spectra were analyzed using HYPERMET PC software and the chemical composition is calculated using an Excel-macro that provides the concentrations as molar and weight percentages, as well as the corresponding masses of the oxides. The validation of the analytical method is demonstrated with the analysis of a reference material. The results show that the distribution of the studied metals (Pb, Zn, Cu, Cd, Cr Ni, and As) in the basin is dependent on location with a very significant contamination by Pb, Zn, Cu, Cd, Cr, and Ni close to the lead mine sites.

The cave of Han-sur-Lesse is a shallow-hole (gouffre de Belvaux) – resurgence (trou de Han) system excavated by the Lesse river in the Givetian limestones (380 to 360 Ma) of the Boine Massif. Since 2004, a large experimental spread (17 recording stations) was developed on the site, aiming to better understand the hydro-geological behaviour of this karstic system. Hydrographs, piezometric data and physico-chemical parameters were recorded. Tracer tests, during different hydrological conditions, were carried out. This information allowed us to suggest a conceptuel model of the hydrogeology of the Boine massif. During low water conditions, the underground Lesse course can be compared to a one-dimensional drain with a succession of underground river stretches and flooded areas. Underground river stretchs are accessible and can be easily proportioned. It is not the case for flooded areas. Based on comments of divers, these areas are considered as free surface high flow sections developed in intensely fractured and karstified limestones. One of the aims of this work is to proportion these areas. A tracer test with sampling sites located upstream and downstream of flooded areas was carried out in September '09 in low water conditions. The measured breakthrough curves showed that the crossing of flooded areas led to a slowing down of the tracer cloud and a delay in the restitution of a part of the tracer. The tracer results were modelled with the river flow and transport model OTIS (One-dimensional Transport with Inflow and Storage) (Runkel, 1998). This model is based on the temporary storage processes described by Bencala and Walter (1983). In our model, the flooded areas of the Han-sur-Lesse karstic system are considered as high flow sections composed of a sum of small flow sections in interaction with storage zones due to the heterogeneousness of the flow media. The fitting of the modelled curves on the experimental data are accurate showing that the model could be used, Le réseau karstique de Han-sur-Lesse est un système "perte (gouffre de Belvaux) – résurgence (trou de Han)" de la Lesse développé au sein des calcaires givetiens du massif de Boine (Han-sur-Lesse). Une caractérisation du comportement hydrogéologique de ce massif a été entreprise dès novembre 2004. Celle-ci repose sur une méthodologie essentiellement expérimentale. Un dispositif de mesure permanent, constitué de dix-sept stations d'enregistrement (stations de jaugeage, stations limnimétriques, stations piézométriques), a été mis en place. Des campagnes d'échantillonnage ont été effectuées en périodes de basses et de hautes eaux afin de définir le faciès physico-chimique des eaux du système. Plusieurs essais de traçage ont été réalisés, dans divers contextes hydrologiques, afin d'étudier la dimension transmissive du système. Les résultats de l'ensemble de ces mesures nous permettent de proposer un schéma conceptuel du comportement hydrogéologique du massif de Boine. Durant les périodes de basses eaux, le cours souterrain de la Lesse peut être assimilé à un système unidimensionnel hétérogène consistant en une alternance de tronçons de rivière souterraine et de zones noyées à haut degré de karstification. Les tronçons de rivière sont accessibles et aisément dimensionnables. Les zones noyées, grands volumes de roches, intensément fracturés, karstifiés et hautement transmissifs uniquement accessibles en plongée, sont, quant à elles, difficiles à dimensionner. Un essai de traçage avec échantillonnage à l'amont et à l'aval de ces zones noyées a été réalisé en septembre 2009 dans des conditions d'étiage. Les courbes de restitution mesurées démontrent que la traversée des zones noyées induit un ralentissement significatif du nuage de traceur et accroît les effets de retard. Les résultats de cet essai de traçage ont été modélisés à l'aide du logiciel Otis (One-Dimensional Transport with Inflow and Storage) (Runkel, 1998). Ce modèle repose sur les processus d'emmagasinement tem, (DOCSC04) -- FUNDP, 2011

Several vector-borne and zoonotic diseases have emerged or re-emerged in Europe over these last decades. Besides climate change that influences disease risk at a regional scale, landscape changes could be responsible for local heterogeneities in disease risk. Spatial epidemiology tries to understand and predict spatial variations in disease risk by using spatial tools and spatially-explicit modelling methods. This study investigated the impact of fine-grained landscape patterns on the transmission of vector-borne and zoonotic infections in terms of habitat suitability for vectors and/or hosts and of exposure of people to infectious agents. This was studied through three human diseases emerging or at risk of re-emergence in Europe: the rodent-borne Puumala hantavirus, the tick-borne Lyme borreliosis and the mosquito-borne malaria infections. Statistical models were first used to study the relationships between environmental variables and host abundance, host prevalence, and human cases of Puumala hantavirus. Environmental factors were also combined with socio-economic factors to explain Puumala hantavirus and Lyme borreliosis incidence rates. The combination of factors explaining disease transmission and the complexity of such systems led to the development of an innovative, spatially-explicit modelling method: multi-agent simulation (MAS). The MALCAM simulation model was developed to assess the risk of malaria re-emergence in southern France and simulates spatial and temporal variations in contact rate between people and potential malaria vectors. The effect of changes in potential drivers of malaria re-emergence was also simulated. The different case studies showed that fine-grained landscape patterns influence the presence and abundance of vectors and hosts. Moreover, environmental conditions may also influence disease transmission through pathogen dispersal and the exposure of people to infectious agents. Finally, this study showed that people-vector contacts not, (GEOG 3) -- UCL, 2009

"Soil is a non-renewable resource (…) vital to human activities and ecosystem survival" (EC, 2006). Soil protection requires studies and monitoring based on indicators of its quality. Soil organic matter content (SOM) is one the most relevant of these indicators. However, the inventory of soil organic carbon (SOC), the main component of SOM, is challenging at the regional scale due to its inherent large spatial variability and its slow dynamics. Uncertainties can reach high levels preventing both the detection of significant SOC changes through time and the identification of the driving forces involved. This, in turn, undermines the ability to implement judicious policies for SOC conservation or sequestration. Given such a context, this thesis aims to improve the understanding of long-term SOC dynamics in agricultural soils at the regional scale. The specific objectives are: (i) to detect the SOC stock changes under agriculture in southern Belgium between 1955 and 2005, (ii) to quantify the uncertainties and validate the methodology used, and (iii) to discriminate the driving forces involved in the observed SOC evolution. This thesis shows that significant changes in SOC stocks can be detected thanks to the stratification of the study area into spatial homogeneous units (based on land use, soil type, climate and agricultural region) and to the re-sampling of soil profiles from the 1950s. Despite uncertainties on the SOC stock assessment mainly arising from the laboratory analyses and the spatial variability, an opposite behaviour in the change in SOC stock is found between units under cropland (–12% on average in the plough layer) and units under grassland (+20% in the 0-30cm layer). The main driving forces of SOC evolution are the agricultural management for cropland and the soil texture (clay content) for grassland. The impact of climate change (i.e. of the changes in the mean annual temperature and precipitation) is of minor importance. Results also shows that th, "Le sol est une ressource non renouvelable (...) essentielle à l’activité humaine et à la survie des écosystèmes" (CE, 2006). Sa préservation nécessite une étude et un suivi basés notamment sur des indicateurs de sa qualité. Le contenu en matière organique du sol (MOS) est un des plus importants de ces indicateurs. Cependant, réaliser l’inventaire du carbone organique du sol (COS), principal composant de la MOS, représente un défi à l’échelle régionale du fait de son importante variabilité spatiale et de sa lente dynamique. Les incertitudes peuvent atteindre des niveaux tels qu’elles empêchent non seulement la détection d’un changement de COS à travers le temps mais également l’identification des facteurs impliqués. La possibilité de mettre en œuvre des politiques judicieuses pour conserver ou augmenter le COS en est ainsi rendue plus difficile. Dès lors, cette thèse a pour but principal d’améliorer la compréhension de la dynamique du COS à long terme dans les sols agricoles à l’échelle régionale. Les objectifs de cette étude sont les suivants : (i) détecter les changements de stock de COS des sols agricoles en Wallonie (Belgique) entre 1955 et 2005, (ii) quantifier les incertitudes et valider la méthodologie utilisée, et (iii) identifier les facteurs explicatifs de l’évolution en COS observée. Cette thèse démontre que des changements significatifs de stock de COS peuvent être détectés grâce à la stratification de la zone d’étude en unités homogènes spatiales (basées sur l’utilisation du sol, le type de sol, le climat et la région agricole) ainsi qu’au ré-échantillonnage des profils de sol des années cinquante. Malgré les incertitudes pesant sur l’estimation du stock de COS, résultant principalement des analyses de laboratoire et de la variabilité spatiale, une évolution divergeante du stock de COS est observée dans les unités sous culture (–12% en moyenne dans l’horizon de labour) et les unités sous prairie (+20% dans la couche 0-30cm). Les principaux facteurs expl, (GEOG 3) -- UCL, 2009

The Camargue, a region in southern France, is considered a potential site for malaria reemergence. All the suitable factors of the disease transmission system are present-competent mosquito vectors, habitats for their breeding, and susceptible people-except for the parasite. The objective of this study was to test potential drivers of malaria reemergence in this system after possible changes in biological attributes of vectors, agricultural practices, land use, tourism activities, and climate. Scenarios of plausible futures were formulated and then simulated using a spatially explicit and dynamic multiagent simulation: the MALCAM model. Scenarios were developed by varying the value of model inputs. Model outputs were compared based on the contact rate between people and potential malaria vectors, and the number of new infections in case of reintroduction of the parasite in the region. Model simulations showed that the risk of malaria reemergence is low in the Camargue. If the disease would reemerge, it would be the result of a combination of unfavorable conditions: introduction of a large population of infectious people or mosquitoes, combined with high levels of people-vector contacts resulting from significant changes in land use, tourism activities, agricultural policies, biological evolution of mosquitoes, and climate changes. The representation in the MALCAM model of interactions and feedbacks between different agents, and between agents and their environment, led in some cases to counterintuitive results. Results from scenario analyses can help local public health authorities in policy formulation.

In some countries across the globe, tropical forest cover is increasing. The national-scale reforestation of Vietnam since 1992 is assumed to contribute to this recovery. It is achieved, however, by the displacement of forest extraction to other countries on the order of 49 (34-70) M m(3), or approximately 39% of the regrowth of Vietnam's forests from 1987 to 2006. Approximately half of wood imports to Vietnam during this period were illegal. Leakage due to policies restricting forest exploitation and displacement due to growing domestic consumption and exports contributed respectively to an estimated 58% and 42% of total displacement. Exports of wood products from Vietnam also grew rapidly, amounting to 84% of the displacement, which is a remarkable feature of the forest transition in Vietnam. Attribution of the displacement and corresponding forest extraction to Vietnam, the source countries or the final consumers is thus debatable. Sixty-one percent of the regrowth in Vietnam was, thus, not associated with displacement abroad. Policies allocating credits to countries for reducing deforestation and forest degradation should monitor illegal timber trade and take into account the policy-induced leakage of wood extraction to other countries.

It is generally recognized that soils represent a major pool in the global C-cycle, as they contain more organic carbon than the atmosphere and biosphere together. As soil organic carbon (SOC) is a dynamic soil property, monitoring SOC is crucial in the framework of international treaties facing climate change (e.g. Kyoto protocol) and directives considering soil quality (e.g. EU Soil Thematic Strategy). More accurate SOC estimates at the regional scale are essential to better understand the significance of the soil reservoir. As detailed SOC maps and an insight into the effects of physical (i.e. soil type and climate conditions) and anthropogenic factors (i.e. land use and land management) on SOC storage are not fully understood yet, this study unraveled the influence of environmental factors on SOC inventories, its distribution with depth, and its change through time. Therefore a new SOC mapping technique, an empirical model-based approach, was developed and allowed the estimation of reliable SOC values for a wide range of landscape units, resulting in complete and spatially detailed SOC maps for Belgium. This method also allowed studying SOC stock changes between 1960 and 2006. The integration of depth as a third dimension in the present spatial - temporal explicit approach provided information on the stability of C and offered the possibility to map SOC until a reference depth free of choice. The results revealed that to a large extent SOC is determined by land use, precipitation, drainage status and clay content. By modelling the vertical SOC distribution and establishing pedotransfer functions (PTF’s), predicting the parameters of this vertical distribution in function of environmental variables, SOC could be modelled in a 3D context. The results show that the influence of land use on SOC is restricted to the topsoil, while soil type determines the vertical SOC distribution. The application of the new SOC mapping technique in a temporal context shows that in t, (GEOG 3) -- UCL, 2009

Although the presence of tick-borne encephalitis (TBE) virus circulating in tick populations depends on large-scale patterns of climate, and the local density of infected ticks depends on the abundance of mammalian hosts, the risk of human infection depends on the access and use by human populations of tick-infested habitats, particularly forests, at the landscape level. We investigated the incidence of reported TBE cases in rural parishes (i.e., municipalities) in Latvia. The following major characteristics of parishes were considered: whether their environment is suitable for tick and tick-host populations (depending on land cover); whether the local human population is likely to enter the forest on a regular base (depending on land use); and whether the spatial distributions of these two aspects are likely to intersect, through access rules (as a function of land ownership). The results indicated that all three aspects are important in explaining and predicting the spatial distribution of TBE cases in the rural areas of Latvia. The concept of landscape is here given new depth by consideration of its physical structure, its use by human populations, and its accessibility as modulated by ownership.

In a semi-arid limestone area, finding additional water resources is a priority. Moreover in the Sierra de Gador-Campo de Dalias, the local economy is booming and mainly based on groundwater resources. In common with other semi-arid to arid regions in particular along both sides of the Mediterranean are facing the same difficulties in balancing economic and natural resources. Aquifers are often overexploited and the demand is still growing. Hence, for sustainable development, water resources must be evaluated. Long term estimates are generally based on global assessment of diffuse recharge. This is somehow paradoxal as extreme events are recognized to preferentially recharge the aquifer. We show that the selectivity of deuterium excess to monthly precipitation volume allowed estimating the return period of precipitation leading to aquifer recharge at 0.9-4.9 years. Still moderate rainfall, which occurs more frequently, represents c. 60-90% of the total precipitation volume. This thesis aims to contribute to the understanding of the groundwater recharge system with particular attention to runoff processes and a focus on runoff as a component of water balance in semi arid areas. Runoff is usually regarded as negligible in the recharge system of the semi-arid aquifers. Generally rare and discontinuous, the runoff process is difficult to monitor. The approach used is to first evaluate the main factors explaining the occurrence of runoff reaching the bottom of the hillslope for several representative sites in the study area (0.3-20 ha). It was demonstrated that runoff events depend on thresholds i.e. rainfall depth per event, the antecedent precipitation index over 20 days (API20) and soil surface characteristics. Then, a simple rainfall/runoff model was adapted and validated at the hillslope scale. The expert-based model allowed acceptable results for predicting runoff at this scale. Finally, the hillslope model was extrapolated to the catchment scale (26 km²) in order, (GEOG 3) -- UCL, 2009

The sequestration of silicon in soil clay-sized iron oxides may affect the terrestrial cycle of Si. Iron oxides indeed specifically adsorb aqueous monosilicic acid (H4SiO40), thereby influencing Si concentration in soil solution. Here we study the impact of H4SiO40 adsorption on the fractionation of Si isotopes in basaltic ash soils differing in weathering degree (from two weathering sequences, Cameroon), hence in clay and Fe-oxide contents, and evaluate the potential isotopic impact on dissolved Si in surrounding Cameroon rivers. Adsorption was measured in batch experiment series designed as function of time (0-72 h) and initial concentration (ic) of Si in solution (0.61-1.18 mM) at 20 degrees C, constant pH (5.5) and ionic strength (I mM). After various soil-solution contact times, the delta Si-30 vs. NBS28 compositions were determined in selected solutions by MC-ICP-MS (Nu Plasma) in medium resolution, operating in dry plasma with Mg doping with an average precision of +/-0.15 parts per thousand (+/-2 sigma(SEM)). The quantitative adsorption of H4SiO40 by soil Fe-oxides left a solution depleted in light Si isotopes, which confirms previous study on synthetic Fe-oxides. Measured against its initial composition (delta Si-30 = +0.02 +/- 0.07 parts per thousand (+/-2 sigma(SD))), the solutions were systematically enriched in Si-30 reaching maximum delta Si-30 values ranging between +0.16 parts per thousand and +0.95 parts per thousand after 72 h contact time. The enrichment of the solution in heavy isotopes increased with increasing values of three parameters: soil weathering degree, iron oxide content, and proportion of short-range ordered Fe-oxide. The Si-isotopic signature of the solution was partly influenced by Si release, possibly through mineral dissolution and Si desorption from oxide surfaces, depending on soil type, highlighting the complex pattern of natural soils. Surrounding Cameroon rivers displayed a mean Si-isotopic signature of +1.19 parts per thousa

Soil monitoring programmes face significant challenges as there is an important trade-off between detecting significant changes in soil properties on the one hand (which can be achieved by minimizing variability by higher sampling density or stratification approaches), and identifying the driving forces responsible for these changes on the other hand (which requires enough variability). This study aims to reconcile these two objectives by identifying the driving forces of soil organic carbon (SOC) evolution over a long period, based on an extensive but stratified soil monitoring programme. Data at both the finest level (questionnaires to the farmers) and the large scale (agricultural census, climate and soil databases for southern Belgium) were used in a cluster analysis, multiple linear regressions and mixed odels in order to discriminate between the driving forces involved. Results indicated that the negative 'baseline effect' (i.e. the inversely proportional effect of the initial SOC content on the SOC evolution) was responsible for an important part of the SOC variability. Consequently, the systems are not at steady state when starting the observations, although this assumption is used by most SOC dynamic models. Moreover, the baseline effect resulted in a trend of the soils to converge towards a regional SOC stock which significantly differed according to land use (36.4 t C ha-1 for the plough depth of cropland and 92.2 t C ha-1 for the 0-30 cm layer of grassland). Despite this strong effect, the main driving forces of the SOC decrease of cropland (-0.2 t C ha-1 yr-1) and SOC increase of grassland (+0.2 t C ha-1 yr-1) over a period of 50 years were discriminated. The agricultural management (cropland) and the clay content (grassland), together with the change in precipitation (to a lesser degree for cropland) were highlighted as the predominant factors involved in SOC evolution, when land use change is excluded. The use of questionnaires allowed to better under

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 (ENS). When applied to Belgium, the model results are satisfactory to good after an adaptation of the decision rules (0.90

In most studies concerning the carbon ( C) exchange between soil and atmosphere only the topsoil (0-0.3 m) is taken into account. However, it has been shown that important amounts of stable soil organic carbon (SOC) are also stored at greater depth. Here, we developed a quantitative model to estimate the evolution of the distribution of SOC with depth between 1960 ( database 'Aardewerk') and 2006 in northern Belgium. This temporal analysis was conducted under different land use, texture and drainage conditions. The results indicate that intensified land management practices seriously affect the SOC status of the soil. The increase in plough depth and a change in crop rotation result in a significant decrease of C near the surface for dry silt loam cropland soils, (i.e. 1.02 +/- 0.23 kg C m(-2) in the top 0.3 m between 1960 and 2006). In wet to extremely wet grasslands, topsoil SOC decreased significantly, indicating a negative influence of intensive soil drainage on SOC stock. This resulted in a decline of SOC between 1960 and 2006 in the top 1m, ranging from 3.99 +/- 2.57 kg C m(-2) in extremely wet silt loam soils to 2.04 +/- 2.08 kg C m(-2) in wet sandy soils. A slight increase of SOC stock is observed under dry to moderately wet grasslands at greater depths corresponding to increased livestock densities in the region. The increase of SOC in the top 1m under grassland ranges from 0.65 +/- 1.39 kg C m(-2) in well drained silt loam soils to 2.59 +/- 6.49 kg C m(-2) in moderately drained silt loam soils over entire period.

Terraces are a common feature of Mediterranean landscapes. In many places they are no longer maintained so that the number of intact terraces is in prolonged decline. The aim of this paper is to examine the effect of terrace removal and failure on hydrological connectivity and peak discharge in an agricultural catchment (475 ha) in south-east Spain. The situation of 2006 is compared to that in 1956 and to a scenario without terraces (S2). The spatial distribution of concentrated flow was mapped after four storms in 2006. The degree of connectivity was quantified by means of connectivity functions and related to storm characteristics, land use and topography. For 1956, 2006 and scenario S2, connectivity functions and peak discharge to the river were determined for a storm with a return period of 8.2 years. The results show that the decrease in intact terraces has led to a strong increase in connectivity and discharge. The contributing area to the river system has increased by a factor 3.2 between 1956 and 2006. If all terraces were to be removed (scenario S2), the contributing area may further increase by a factor 6.0 compared to 2006. The spatial extent of concentrated flow and the degree of connectivity are related to storm magnitude as expressed by the erosivity index (EI30). Although a large part of the concentrated flow (25-50%) occurs on dirt roads, it appears that croplands become a major source of runoff with increasing rainfall. The results suggest that connectivity theory can be used to improve rainfall-runoff models in semi-arid areas. Copyright (c) 2009 John Wiley & Sons, Ltd.

Soil degradation processes have dramatically increased in their extent and intensity over the last decades. Progressively, actions have been taken in order to evaluate and reduce the major threats that have already wreaked havoc on soil conditions. Efficient and standardized monitoring of soil conditions is thus required but soil quality research is facing an important technological challenge because of the number of properties involved in soil quality. The objective of the present review is to examine critically the suitability of near-infrared reflectance spectroscopy (NIRS) as a tool for soil quality assessment. We first detail the soil quality-related parameters (chemical, physical and biological) that can be predicted with NIRS through laboratory measurements. The ability of imaging NIRS (airborne or satellite) for mapping a minimum data set of soil quality is also discussed. Then we review the most recent research using soil reflectance spectra as an integrated measure of soil quality, from global site classification to the prediction of specific soil quality indices. We conclude that imaging NIRS enables the direct mapping of some soil properties and soil threats, but that further developments to solve several technological limitations identified are needed before it can be used for soil quality assessment. The robustness of laboratory NIRS for soil quality assessment allows its implementation in soil monitoring networks. However, its routine use requires the development of international soil spectral libraries that should become a priority for soil quality research.

Many studies attribute the effects of vegetation in reducing soil erosion rates to the effects of the above-ground biomass. The effects of roots on topsoil resistance against concentrated flow erosion are much less studied. However, in a Mediterranean context, where the above-ground biomass can temporarily disappear because of fire, drought or overgrazing, and when concentrated flow erosion occurs, roots can play an important role in controlling soil erosion rates. Unfortunately, information on Mediterranean plant characteristics, especially root characteristics, growing on semi-natural lands, and knowledge of their suitability for gully erosion control is often lacking. A methodological framework to evaluate plant traits for this purpose is absent as well. This paper presents a methodology to assess the suitability of plants for rill and gully erosion control and its application to 25 plant species, representative for a semi-arid Mediterranean landscape in southeast Spain. In this analysis determination of suitable plants for controlling concentrated flow erosion is based on a multi-criteria analysis. First, four main criteria were determined, i.e. (1) the potential of plants to prevent incision by concentrated flow erosion, (2) the potential of plants to improve slope stability, (3) the resistance of plants to bending by water flow and (4) the ability of plants to trap sediments and organic debris. Then, an indicator or a combination of two indicators was used to assess the scores for the four criteria. In total, five indicators were selected, i.e. additional root cohesion, plant stiffness, stem density, the erosion-reducing potential during concentrated flow and the sediment and organic debris obstruction potential. Both above- and below-ground plant traits were taken into account and measured to assess the scores for the five indicators, i.e. stem density, sediment and organic debris obstruction potential, modulus of elasticity of the stems, moment of inertia of

The effectiveness of water harvesting systems collecting surface runoff form rangeland hillslopes in semi-arid regions is difficult to predict, since the hydrological response at the outlet depends on the heterogeneity of hydrological processes. The lack of continuous runoff pathways, due to the irregular spatial patterns of soil properties and the variety of antecedent soil moisture conditions directly influence runoff generation and control discharge into the water harvesting cisterns. The aim of this paper is to evaluate the effectiveness of semi-arid hillslopes in generating runoff for water harvesting systems. Runoff was estimated by the STREAM expert-based model which was applied to three semi-arid hillslopes (0.4 to 6 ha). On the one hand the STREAM model rules were adapted to the regional conditions i.e. an antecedent precipitation index was adjusted to local soil moisture conditions and the rainfall duration was defined as the total rainfall event quantity and the effective rainfall duration (P-tot/t(eff)). On the other hand, the distribution of rock outcrop and vegetation cover along the slopes was used to define homogeneous hydrological units. Final infiltration capacities were attributed to these hydrological units based on values found in the literature. The prediction performances are acceptable for the three water harvesting systems with an RMSE of 13.9 m(3). It was shown that the rainfall/runoff model was more sensitive to the duration of the storm than to the antecedent soil moisture conditions. The use of a unique set of hydrological parameters for the three water harvesting systems on representative hillslopes allows the runoff prediction from any rangeland hillslope within the same region. Furthermore, the spatial patterns of soil surface characteristics are crucial for collecting runoff at the outlet of the system. Model runs demonstrated that degradation of vegetation and sealing of very small areas within flow paths can lead to an increase of

Restoration of degraded land in the Southern Ecuadorian Andes has led to alterations in the functioning of degraded catchments. Recovery of vegetation on areas affected by overgrazing, as well as the reforestation or afforestation of gully areas have given rise to modifications of hydrological connectivity within the catchments. Recent research has highlighted the ability of gully channels to trap sediment eroded from steep slopes, especially if vegetation is established along the gully bed. However, vegetation cover not only induces sediment deposition in the gully bed, but may also have a potential to reduce runoff water volume. The performance of gully beds in reducing the transfer of runoff was investigated by conducting controlled concentrated flow experiments in the field. Experimental field data for nine gullies were derived by pouring concentrated inflow into the upstream end and measuring the outflow at the downstream end of the channel. Two consecutive flow experiments per gully were carried out, so that data for dry and wet soil conditions were collected. The hydrological response to concentrated flow was estimated for each experiment by calculating its cumulative infiltration coefficient, IC (%). The results showed a great difference in IC between dry and wet soil conditions. The IC for wet soil conditions was on average 24%, whereas it was 60% for dry conditions. Gullies with more than 50% surface vegetation cover exhibit the highest cumulative infiltration coefficients (81% for dry runs, and 34% for wet runs), but runoff transmission losses were not as clearly related to vegetation cover as sediment storage as shown in Molina et al. (2009). The experimental field data of 16 experiments were used to calibrate a hydrological model developed by Fiener and Auerswald (2005) in order to simulate the transfer of concentrated flow along the gully beds. The calibrated model was able to simulate the transfer of runoff water well, as the error on the simulated to

The rate of exchange of CO2 between the soil and the atmosphere depends on the stability of the organic carbon stored in the soil. Recent studies show that carbon stored in the subsoil is characterised by larger turnover times than the carbon stored in the topsoil. Consequently, identification of the depth at which high/low amounts of SOC are stored is essential for applying sustainable management of the soil in the light of global warming and related threats. This study investigates the depth distribution of SOC in relation to land use and soil type based on a large dataset for Flanders (Belgium). Soil type determines the SOC content along the entire profile. On the contrary, land use appears to have a strong influence on SOC content in the top layers of the profile, but doesn't play a significant role at the bottom of the profile (> 1 m depth). SOC content near the surface of the profile is remarkably higher in fine (clay) textured soils than in coarse (sand) textured soils and tends to increase by increasing soil wetness under sand and silt textured soils. SOC at the bottom of the profile increases as well by increasing soil wetness, but only in fine (clay and silt) textured soils. The rate of decline of SOC content with depth depends on texture and land use. Under forest this decline is remarkably fast, although less so in the more sandy soil types. The overall model predicts the distribution of SOC density by depth using land use and soil type information and allows in its integrated form the estimation of SOC stocks that can be represented on SOC maps until a reference depth free of choice. Applying this model, based on a three-dimensional spatial distribution approach, the total amount of SOC stored in Flanders is calculated at 62.20 +/- 0.72 Mt C for the top 0.3 m and 103.19 +/- 1.27 Mt C for the top 1 m. (C) 2009 Elsevier B.V. All rights reserved.

Soil loss on arable agricultural land is typically an order of magnitude higher than under undisturbed native vegetation. Although there have been several recent attempts to quantify these accelerated fluxes at the regional, continental and even global scale, all of these studies have focused on erosion by water and wind and no large scale assessment of the magnitude of tillage erosion has been made, despite growing recognition of its significance on agricultural land. Previous field scale simulations of tillage erosion severity have relied on use of high resolution topographic data to derive the measures of slope curvature needed to estimate tillage erosion rates. Here we present a method to derive the required measures of slope curvature from low resolution, but large scale, databases and use high resolution topographical datasets for several study areas in the UK to evaluate the reliability of the approach. On the basis of a tillage model and land-use databases, we estimate the mean gross tillage erosion rates for the part of Europe covered by the CORINE database (6.5% of global cropland) and we obtained an average of 3.3 Mg ha(-1) y(-1), which corresponds to a sediment flux of 0.35 Pg y(-1). Water erosion rates derived for the same area are of a similar magnitude. This redistribution of soil within agricultural fields substantially accelerates soil profile truncation and sediment burial in specific landscape positions and has a strong impact on medium-term soil profile evolution. it is, therefore, clear that tillage erosion must be accounted for in regional assessments of sediment fluxes and in analyses that employ these in the analysis of land management strategies and biogeochemical cycles. Copyright (C) 2009 John Wiley & Sons, Ltd.

The quantification of silicon isotopic fractionation by biotic and abiotic processes contributes to the understanding of the Si continental cycle. In soils, light Si isotopes are selectively taken up by plants, and concentrate in secondary clay-sized minerals. Si can readily be retrieved from soil solution through the specific adsorption of monosilicic acid (H4SiO40) by iron oxides. Here, we report on the Si-isotopic fractionation during H4SiO40 adsorption on synthesized ferrihydrite and goethite in batch experiment series designed as function of time (0-504 h) and initial concentration (ic) of Si in solution (0.21-1.80 mM), at 20 degrees C, constant pH (5.5) and ionic strength (1 mM). At various contact times, the delta Si-29 vs. NBS28 compositions were determined in selected solutions (ic = 0.64 and 1.06 mM Si) by MC-ICP-MS in dry plasma mode with external Mg doping with an average precision of +/- 0.08 parts per thousand (+/- 2 sigma(SEM)). Per oxide mass, ferrihydrite (74-86% of initial Si loading) adsorbed more Si than goethite (37-69%) after 504 h of contact over the range of initial Si concentration 0.42-1.80 mM. Measured against its initial composition (delta Si-29 = +0.01 +/- 0.04 parts per thousand (+/- 2 sigma(SD))), the remaining solution was systematically enriched in Si-29, reaching maximum delta Si-29 values of +0.70 +/- 0.07 parts per thousand for ferrihydrite and +0.50 +/- 0.08 parts per thousand for goethite for ic 1.06 mM. The progressive 29 Si enrichment of the solution fitted better a Rayleigh distillation path than a steady state model. The fractionation factor (29)epsilon(+/- 1 sigma(SD)) was estimated at -0.54 +/- 0.03 parts per thousand for ferrihydrite and -0.81 +/- 0.12 parts per thousand for goethite. Our data imply that the sorption of H4SiO40 onto synthetic iron oxides produced a distinct Si-isotopic fractionation for the two types of oxide but in the same order than that generated by Si uptake by plants and diatoms. They further sugges

A multi-agent simulation (MAS) was developed to assess the risk of malaria re-emergence in the Camargue in southern France, a non-endemic area where mosquitoes of the genus Anopheles (Culicidae) live. The contact rate between people and potential malaria vectors, or the human biting rate, is one of the key factor to predict the risk of re-emergence of malaria, would the parasite be introduced in the region. Our model (called MALCAM) represents the different agents that could influence malaria transmission in the Camargue people, mosquitoes, animal hosts and the landscape - in a spatially explicit environment. The model simulates spatial and temporal variations in human biting rate at the landscape scale. These variations depend on the distribution of people and potential vectors, their behaviour and their interactions. A land use/cover map was used as a cellular-spatial support for the movements of and interactions between mobile agents. The model was tested for its sensitivity to variations in parameter values, and for the agreement between field observations and model predictions. The MALCAM model provides a tool to better understand the interactions between the multiple agents of the disease transmission system, and the land use and land cover factors that control the spatial heterogeneity in these interactions. It allows testing hypotheses and scenarios related to disease dynamics by varying the value of exogenous biological, geographical, or human factors. This application of agent-based modelling to a human vector-borne disease can be adapted to different diseases and regions. (C) 2008 Elsevier B.V All rights reserved.

Estimation of spatially averaged denudation rates from cosmogenic nuclide concentrations in sediments depends on the surface production rates, the scaling methods of cosmic ray intensities, and the correction algorithms for skyline, snow and vegetation shielding used to calculate terrestrial cosmogenic nuclide production. While the calculation of surface nuclide production and application of latitude, altitude and palaeointensity scaling algorithms are subjects of active research, the importance of additional correction for shielding by topographic obstructions, snow and vegetation is the subject of ongoing debate. The derivation of all additional correction factor for skyline shielding for large areas is still problematic. One important issue that has yet to he addressed is the effect of the accuracy and resolution of terrain representation by a digital elevation model (DEM) on topographic shielding collection factors. Topographic metrics scale with the resolution of the elevalion data, and terrain smoothing has a potentially large effect on the correction of terrestrial cosmogenic nuclide production rates for skyline shielding. For rough, high-relief landscapes, the effect of terrain smoothing call easily exceed analytical errors, and should be taken into account. Here we demonstrate the effect of terrain smoothing on topographic shielding correction factors for various topographic settings, and introduce an empirical model for the estimation of topographic shielding factors based on landscape metrics. Copyright (C) 2008 John Wiley and Sons, Ltd.

The spatial estimation of Soil Organic Carbon (SOC) at large scale in outdoor condition is an important issue. It has been largely demonstrated that diffuse reflectance spectroscopic techniques, are efficient for SOC determination in field conditions. However these methods are influenced by disturbing factors such as soil water content, vegetation residues and surface roughness, the later being the object of this study. Our laboratory experiments showed that the accuracy of SOC prediction from shadowed soil samples with spectroscopy techniques decreases with increasing soil shadow. In this study a new methodology using a digital camera for identifying and correcting the effect of soil shadow on field reflectance spectra measured with an Analytical Spectral Devices (ASD) during field campaign in bare crop lands has been elaborated and tested. Results showed that the proposed shadow correction method enables improving significantly SOC prediction accuracy and performs better than traditionally used methods consisting in automatic signal processing., Anglais

Anthropogenic pressures on the Earth System have reached a scale where abrupt global environmental change can no longer be excluded. We propose a new approach to global sustainability in which we define planetary boundaries within which we expect that humanity can operate safely. Transgressing one or more planetary boundaries may be deleterious or even catastrophic due to the risk of crossing thresholds that will trigger non-linear, abrupt environmental change within continental- to planetary-scale systems. We have identified nine planetary boundaries and, drawing upon current scientific understanding, we propose quantifications for seven of them. These seven are climate change (CO2 concentration in the atmosphere <350 ppm and/or a maximum change of +1 W m-2 in radiative forcing); ocean acidification (mean surface seawater saturation state with respect to aragonite ≥ 80% of pre-industrial levels); stratospheric ozone (<5% reduction in O3 concentration from pre-industrial level of 290 Dobson Units); biogeochemical nitrogen (N) cycle (limit industrial and agricultural fixation of N2 to 35 Tg N yr-1) and phosphorus (P) cycle (annual P inflow to oceans not to exceed 10 times the natural background weathering of P); global freshwater use (<4000 km3 yr-1 of consumptive use of runoff resources); land system change (<15% of the ice-free land surface under cropland); and the rate at which biological diversity is lost (annual rate of <10 extinctions per million species). The two additional planetary boundaries for which we have not yet been able to determine a boundary level are chemical pollution and atmospheric aerosol loading. We estimate that humanity has already transgressed three planetary boundaries: for climate change, rate of biodiversity loss, and changes to the global nitrogen cycle. Planetary boundaries are interdependent, because transgressing one may both shift the position of other boundaries or cause them to be transgressed. The social impacts of transgressing

An urban microeconomic model of households evolving in a 2D cellular automata allows to simulate the growth of a metropolitan area where land is devoted to housing, road network and agricultural/green areas. This system is self-organised; based on individualistic decisions of economic agents who compete on the land market, the model generates a metropolitan area with houses, roads, and agriculture. Several simulations are performed. The results show strong similarities with physical Dieletric breackdown models (DBM). In particular, phase transitions in the urban morphology occur when a control parameter reaches critical values. Population density in our model and the electric potential in DBM play similar roles, which can explain these resemblances.

The objective of this study was to better understand the linkages between spatial patterns of forest use, land use, and rates of deforestation. We focused on a region of the Brazilian Amazon characterized by a variety of spatial patterns of deforestation and that experienced rapid deforestation in the last decade: the colonization project "Pedro Peixoto" in the extreme East of Acre State. By combining time series of remote sensing data and household survey data, we tested the hypothesis that each spatial pattern of deforestation is associated with specific socio-economic characteristics of land managers. The statistical results support our hypothesis. However, spatial patterns of deforestation are not a consequence of the main economic activities. Rather, spatial patterns of forest use are linked to the pre-conceived design of the settlement project. The main economic activities are influenced by factors such as the property size, their location and disposition, and the availability of infrastructure. (C) 2008 Elsevier Ltd. All rights reserved.

The first part of this thesis aims at defining the conditions triggering muddy floods in the Belgian loess belt. On average, each municipality is confronted with 3.6 muddy floods each year. Annual costs associated with their off-site impacts are estimated at € 16-172 millions for the entire Belgian loess belt. A topographic threshold is derived to predict the source areas of muddy floods. Furthermore, the storms required to produce a flood are, on average, smaller in May and June (25 mm) than between July and September (46 mm). This difference is explained by the variability of soil surface characteristics that determine the runoff potential of cultivated soils (soil cover by crops and residues, soil surface crusting and roughness). Steady state infiltration rates of cropland and grassed areas were characterised in the field using a 0.5 m2-portable rainfall simulator. Overall, grassed areas have a lower infiltration rate (16-23 mm h-1) than croplands (25-52 mm h-1). Muddy floods are mostly observed between May-September because of the coincidence of critical soil surface conditions for runoff generation with the most erosive storms. After an adaptation of its decision rules to the local conditions, the STREAM expert-based model provides satisfactory runoff/erosion predictions at the catchment scale. The second part of the thesis aims at evaluating the effectiveness of measures to control muddy floods. A modelling case-study showed that peak discharge was reduced by more than 40% by installing a grassed waterway and a dam at the outlet of a 300 ha-catchment. Monitoring the same catchment (2002-2007) demonstrated that the grassed waterway as well as three dams prevented any muddy flood in the downstream village despite the occurrence of several extreme storms (with a maximum return period of 150 years). Peak discharge was reduced by 69%. Specific sediment yield dropped from 3.5 t ha-1 yr-1 to a mean of 0.5 t ha-1 yr-1 after the installation of the control measures, th, (GEOG 3) -- UCL, 2008

Changes in land use and land cover are associated with many environmental issues observed on the earth’s surface. In the last decades, these changes were unprece-dented, mainly in tropical forest areas. The Brazilian Amazon, the world’s largest tropical forest, lost around 200.000 km² of primary forest in the last ten years (INPE, 2005). Considering this, and the consequences caused by this deforestation, it is important to know and define correctly the responsible agents, aiming at better pub-lic policies that can help preserve the forest. Searching for indicators that could help to identify the deforestation agents, some studies, such as Mertens and Lambin (1997), suggest that every deforestation process shapes the forest land in a specific way, producing a spatial pattern that can be interpreted as indicative of the agents with specific economic activities. Based on this hypothesis, the objective of this study was to contribute to a better understanding of land change processes in the Amazon forest, investigating the linkages between spatial patterns of deforestation, as visualized in satellite images, and different agents and their specific economic activities. To reach this objective, our methodological approach was based on socio-economic data acquired at a household level combined with data from satellite im-ages. First, different spatial patterns of deforestation were identified on the satellite images, based on the typologies proposed by Husson et al. (1995). Then, some of the identified spatial patterns were isolated and analyzed for specific aspects, such as, the deforestation rate calculated through satellite images. socio-economic character-istics based on household survey data and evolution of land use and land cover based on thematic maps derived from satellite images. In addition, cluster analysis was applied using the socio-economic data (household survey) and land use and land cover data (satellite images) in a search for homogeneous groups related, (GEOG 3) -- UCL, 2008

Human activities may have, through land use and management changes, an impact on the large amounts of carbon sequestered in soils. Increasingly, inventories of Soil Organic Carbon (SOC) stocks are requested at the regional/national level for countries involved in the Kyoto Protocol and as input in biogeochemical models. However, SOC is characterised by a high spatial variability and a slow temporal dynamic, which reduce our ability to detect and explain SOC stock changes. At the regional scale, local (e.g. land use, topography) and global (e.g. climate) driving factors interact in a complex way and are likely to generate high uncertainties. This thesis represents an effort in assessing and detecting SOC stocks and SOC stock changes at the regional scale. Specifically, our objective was to explore two possible strategies to cope with spatial variability: (i) increase the sampling density using a fast analytical technique (reflectance spectroscopy) and (ii) use information on land use change history to decrease spatial variability in landscape units. In the first part of the thesis, we investigate the capabilities of laboratory, portable and imaging spectroscopy to determine SOC concentrations in croplands. It is shown that laboratory and portable spectroscopy can reach accuracy levels comparable to a standard analytical method (Walkley & Black). Imaging spectroscopy, even with somewhat lower performance, can enhance the estimation of mean SOC stocks by providing a very large sampling density. Outside of the controlled environment of a laboratory, portable and imaging spectroscopy fail to demonstrate reasonable calibration stability over a range of soil types and surface conditions. In the second part of the thesis, we found after re-sampling a soil database collected in 1950-1960 that land use change history has a significant impact on SOC dynamic in forest. Building on this, a bookkeeping model based on historical land use maps (1868-2005) and SOC response curves wa, (GEOG 3) -- UCL, 2008

The spatial distribution and properties of rainfed orchards in semi-arid environments result from complex interactions between man and the physical and economical environment. This thesis investigates a number of these interactions in the context of the mechanisation of management practices since the 1950's. It is shown how the practice of clean sweeping (i.e. frequent shallow tillage) influences the orchard water balance and how the removal of traditional soil and water conservation structures affects the connectivity of overland flow to the river system. Although clean sweeping prevents transpiration and competition by weeds, it also constrains the root growth in the plough layer, so that the trees cannot access the water from small rain events. In addition, clean sweeping promotes accelerated soil erosion. It appears that the practice of clean sweeping limits the water availability in orchards on loamy soils with an annual rainfall in the order of 300 mm. It is demonstrated that the presence and properties of rainfed orchards are related to spatial patterns of soil characteristics and climate. The observed decline in conservation structures like terraces and check-dams leads to an increase in the connectivity of water and sediment to the river system. An alternative for these traditional techniques to retain the water and the soil is the application of cover crops. The advantage of cover crops is that they do not limit the field size. A drawback in dry areas is the competition for water and nutrients between the cover crop and the trees. Field evidence and water balance simulations suggest that cover crops are feasible in areas with an annual precipitation of 500 mm or more., (GEOG 3) -- UCL, 2008