Search

Gully erosion is a serious problem at many locations worldwide, but little is known about its importance at large spatial scales. The remote sensing contribution for the spatial assessment of gullies has thus far been confined to visual image interpretation. The current study was conducted to determine whether automatic classification of optical ASTER imagery could accurately discern permanent erosion gullies in the Brazilian Cerrados. A maximum likelihood classifier (MLC) was trained with two classes, gullies and non-gullies, and applied to images of March (wet season) and August (dry season). Moreover, a bi-temporal classification was performed by labelling a pixel as gully when both for the March and August image it was classified as such. Validation was done with a gully map obtained from a panchromatic QuickBird image and field data. For mono-temporal classification, the March image performed much better than the August image, because spectral differences are more pronounced during the wet season. Based on spatial analysis of output maps, the bi-temporal classification performed best in identifying gullies, as user's accuracy was above 90%, while two of 17 actual gullies were not detected and two small locations were erroneously identified as gully. The combination of ASTER bands 1, 2, 3, and 4 gave highest accuracies. It is concluded that accurate automatic identification of permanent gullies is possible with optical satellite data. Because the Cerrados occupy a vast area, it is expected that the approach presented could be applied to larger areas with similar characteristics.

Gully erosion is an extreme process of land degradation operating in different regions of the world. A common way to quantify the susceptibility of land to gully incision is the use of topographical thresholds for different land use types. However, the impact of various management practices in cropland on these thresholds has not been studied to date, although land management may significantly affect runoff production, erosion processes and rates. Here, the impact of different land management practices on gully head development in cropland is studied based on a standardized procedure for topographical threshold analysis: s > kA− b, where s represents the slope gradient of the soil surface, A the drainage area at the gully head, b an exponent and k a coefficient reflecting the resistance of the land to gully head development. A case study area was chosen around Wanzaye, North Ethiopia, where three different cropland management practices were studied in 75 catchments: (i) the catchment-wide use of stone bunds on the contour, (ii) the use of slightly sloping drainage ditches (feses), and (iii) the combined use of stone bunds and feses. The lowest k-values (0.078–0.090) are found for catchments treated with feses, the highest k-values (0.198–0.205) are observed for stone bund catchments, and medium k-values (0.092–0.099) are found for mixed catchments. This finding implies that catchments with the exclusive use of drainage ditches are the most vulnerable to gully head development compared with mixed catchments and stone bund catchments. However, on-site sheet and rill erosion rates are reduced by feses as they lower the gradient of the overland flow lines. Three trends in cropland management around Wanzaye and the wider region are observed: (i) feses are exclusively made on rather steep slopes where small drainage areas lead to the rapid development of gully heads; (ii) stone bunds are constructed on both steeper and gentle sloping cropland; and (iii) larger and gently sloping catchments seem to be most suitable for the combined use of drainage ditches and stone bunds.

The ability to understand gully erosion development is closely related to our ability to quantify the morphology of gullies. At present, various technologies are at hand to collect data at increasing levels of detail. However, many of the developed technologies are time-consuming, difficult to apply or expensive. As an alternative, image-based modelling offers a cost-efficient, flexible and rapid method to quantify gully morphology from photographs taken in the field. In this study, the use of image-based modelling was tested and fine-tuned to quantify the morphology of four gully heads in contrasting biophysical environments prone to gully erosion: two bank gullies in Central Belgium and two permanent gullies in Northern Ethiopia. Ground photographs (n = 88–235) were taken with a reflex Canon EOS 450D camera having a 20 mm wide-angle lens with a fixed focal length. The data collection occurred during days of 30–100% cloud cover and after removing excessive vegetation in the gullies. Processing of the photographs occurred in PhotoScan 1.0.2. software using the semi-automated Structure from Motion–Multi View Stereo (SfM–MVS) workflow, and allowed to produce 3D Digital Elevation Models with accuracies that range from millimetres to centimetres. In addition, for the same surface, 2.5D models were created in ArcGIS. Gully morphological properties were derived and included cross-sections, total volume and volume of undercut walls and soil pipe inlets. For the volume calculation, OPTOCAT software was used. Cross-sections were also quantified by tape meter measurements. When compared to 3D models, cross-sections quantified from tape meter measurements and from 2.5D models underestimate the cross-sectional area by

Extensive soil erosion has already contributed significantly to the impoverishment of land and people throughout the world. The soil lost is deposited in various reservoirs, thus reducing their capacity. Furthermore, essential plant nutrients are also lost along with the eroded topsoil. Modeling provides an approach for quantification of sediment yield. Sediment yield models ranging from empirical to distributed have been developed by many researchers. In this study, an attempt was made to use the soil and water assessment tool (SWAT) model and Geospatial techniques in an integrated way for modeling runoff and sediment yield for Khadakohol and Harsul watersheds in India. The SWAT model was calibrated for the monsoon months of a year and validated for other years. In countries like India, quantification of runoff/sediment yield is mainly constrained by the nonavailability of observed data and hence, regionalization of parameters was attempted, where the calibrated parameters from Khadakohol was used to Harsul and its applicability was assessed in an ungauged context and the results are found to be encouraging.

The abandonment of land is a global problem with environmental and socioeconomic implications. An approach to assess the relationship between land abandonment and a large set of indicators was illustrated in the present study by using data collected in the framework of the European Union DESIRE research project from 808 field sites located in 10 study sites in the Mediterranean region, Eastern Europe, Latin America, Africa and Asia. A total of 48 indicators provided information for biophysical conditions and socioeconomic characteristics measured at the plot level. The selected indicators refer to farm characteristics (family status, land tenure, present and previous types of land-use, soil depth, slope gradient, tillage operations) and to site-specific characteristics including annual rainfall, rainfall seasonality and water availability. Classes were designated for each indicator and a sensitivity score was assigned to each class based on existing research or empirically assessing the importance of each indicator to the land abandonment issue. Questionnaires for each process of land degradation were prepared and data were collected at field site level in collaboration with land users. Based on correlation statistics and multivariate analyses more than ten indicators out of 48 resulted as significant in affecting land abandonment in the studied field sites. Among them, the most important were rainfall seasonality, elderly index, land fragmentation, farm size, selected soil properties, and the level of policy implementation. Results contribute to the development of appropriate tools for assessing the effectiveness of land management practices for contrasting land abandonment.

Soil erosion and sediment deposition widely affect landscape development, particularly in erosion-prone areas with loess-derived soils. Nevertheless, until now, few attempts were made to quantify soil losses and sediment storage over long (centennial or millennial) timescales. In this study, the Holocene alluvial sediment storage in a small river catchment (52 km2) of the Belgian loess belt is estimated, and a preliminary sediment budget for the catchment is presented. In the valley of the Nethen River (c. 13 km long), a detailed survey of the alluvial sediment archive was conducted. Hand augerings and percussion drillings were made along cross-valley transects at 12 locations in the catchment. AMS 14C dating of peat samples provided a temporal framework for the interpretation of the cores. Results show that the thickness of Holocene sediment deposits in the Nethen valley is 4 to 6 m, which corresponds to a total clastic sediment mass of ∼14 × 106 t stored in the valley bottom. Three alluvial units could be distinguished and associated with deposition phases from 9600 to 2900 B.C., 2900 B.C. to A.D. 1000 and A.D. 1000 to present. In contrast to the older sediments (units 1 and 2), deposits from the last 1000 year (unit 3) contain little organic matter. They are seldom intercalated with peat layers, and devoid of tufa. Unit 3 reaches a thickness of c. 2 m, thereby representing 50% of the Holocene sediment mass stored in the alluvial plain. The mean sedimentation rate in the alluvial plain for this last phase is ∼26 t ha− 1 a− 1, which is about tenfold larger than the sedimentation rates calculated for the older Holocene sediment units. Sediment supply towards the alluvial plain has therefore increased tremendously since Medieval times. These results are in contrast to dating results obtained for colluvial sediments in a nearby dry valley within the catchment of the Nethen, where soil erosion and sediment deposition started in the early Iron Age and was already substantial during the Roman Age. This means that there is a time lag of about one millennium between the onset of high sedimentation rates in the upstream area and high deposition rates in the alluvial plain. This is probably caused by a change in coupling (sediment connectivity) between the plateau, slopes, and rivers. As soil erosion proceeds, first the dry zero-order valleys in the catchment act as sediment traps, and only after these are filled sediment reaches the floodplains. The preliminary sediment budget for the Nethen catchment illustrates that 50% of the sediment that was eroded during the Holocene was stored in colluvial deposits, which are mainly located on footslopes and in dry valley bottoms. Another 29% of the sediment mass is stored in the alluvial plain.

A methodology is presented for assessing the seriousness and impact of land degradation, from a historical and a farmer perspective, in regions where data are not available. Farmers have been directly involved in the assessment of soil, productivity and vegetation cover loss over the past decades, both on cropland and on rangeland. The results for the Bolivian mountain valleys in north Chuquisaca show that the intensive use of small cropland fields has increased soil degradation and consequently led to less water and nutrient availability. Due to the subsequent productivity loss many cropland fields have been abandoned. Rangeland is also severely degraded as a result of the excessive removal of vegetation and subsequent soil loss. Farmers are very concerned, but consider the impact of changed rainfall and less available cropland beyond their control. Consequently, no serious initiatives are taken to solve the land degradation problem. This research adduces evidence of increased land degradation in the Bolivian mountain valleys over recent decades, and stresses the need for urgent (integrated) action with regard to soil and water conservation

The rolling hills region of the Chinese Loess Plateau is one of the areas with the highest erosion rates on earth. A striking feature of this area is the occurrence of many large, permanent gullies. A 3.5-km2 catchment was selected to study the processes of erosion and to adapt the storm-based Limburg Soil Erosion Model (LISEM) to the conditions prevailing on the Loess Plateau. Part of this work consisted of mapping and measuring the largest gully headcuts. The amount of loose soil material beneath the headcuts was also estimated. Observations suggest that gully headcuts are relatively stable (i.e., do not migrate rapidly), but that gullies can nevertheless produce significant amounts of sediment during overland flow events. Erosion of headcuts occurs mainly by soil falls in between storms. The loose soil material produced by these soil falls accumulates on the gully bottom. As the LISEM simulates storm erosion, the development of gullies over time can be ignored, and only the amount of material produced by them during runoff events needs to be studied. A digital elevation model (DEM) was used to estimate the position of existing gully heads by applying an adapted form of the Montgomery and Dietrich [Science 255 (1992) 826] index. Using the assumption that headcuts are vertical, it is possible to calculate headcut height from the slope angle map. A simple stability model, which assumes soil falls on gully headcuts to be a function of soil moisture content and headcut height, was applied. This daily-based model can then be used to simulate the accumulation of loose soil material below the headcut. The results show that while the DEM is not accurate enough to allow the detection of individual headcuts, this method can be used to produce a reasonable estimate of the amount of loose soil material available. A map showing the amount of loose soil material accumulated can then serve as input for a storm-based erosion model such as LISEM.

Hydrological extremes are major weather related disasters, but little is known about their long-term patterns in the context of environmental change. Better understanding of damaging rainfall (e.g. rainfall-erosivity events) occurring at different time-scales has important implications for hydrological and land degradation management. The study of the interdecadal variations may help in understanding some of the consequences of abrupt environmental changes over long time periods. Thus, a decadal-scale rainfall erosivity model (DREM), comparable with the Revised Universal Soil Loss Equation (RUSLE), was developed based on a parsimonious interpretation of rain aggressiveness (95th percentile of rainfalls). The DREM was parameterised to capture interdecadal erosivity variability at the Ukkel station (Belgium), which has the longest RUSLE-based rain-erosivity series in Europe (1898–2007). The DREM performed well against decadal RUSLE data, with a coefficient of determination (R2) of 0 72 and a Nash–Sutcliffe efficiency index of 0 71. The model outperformed three well-established models used in this study (R2~0 4). For a spatial evaluation of the DREM, a pattern of decadal rainfall erosivity was provided for an area around Ukkel, which includes the western part of Germany bordering Belgium, and was compared with maps from the RUSLE approach for 1961–1990. The 95th percentile of June–September rainfalls proved to be a better predictor of decadal rainfall erosivity than yearly based precipitation amount. These results lay the foundation for estimating decadal erosivity in the surrounding areas of Ukkle as well as for historical reconstructions where detailed hydrological data are unavailable, and assumptions cannot be met, for physically based models.

As quantitative or spatially distributed studies of environmental change over truly long-term periods of more than 100 years are extremely rare, we re-photographed 361 landscapes that appear on historical photographs (1868-1994) within a 40,000 km(2) study area in northern Ethiopia. Visible evidence of environmental changes apparent from the paired photographs was analyzed using an expert rating system. The conditions of the woody vegetation, soil and water conservation structures and land management were worse in the earlier periods compared to their present conditions. The cover by indigenous trees is a notable exception: it peaked in the 1930s, declined afterwards and then achieved a second peak in the early 21st century. Particularly in areas with greater population densities, there has been a significant increase in woody vegetation and soil and water conservation structures over the course of the study period. We conclude that except for an apparent upward movement of the upper tree limit, the direct human impacts on the environment are overriding the effects of climate change in the north Ethiopian highlands and that the northern Ethiopian highlands are currently greener than at any other time in the last 145 years.

Future climate change is expected to affect wheat yields. However, it is uncertain if the overall change in climate will result in wheat yield increases or decreases. This is due to the opposing effects of temperature, precipitation, and CO2 concentration on wheat yields. In this study, a meta-analysis of simulated yield change was conducted to identify the levels of temperature, precipitation and CO2 concentration that result in increasing or decreasing wheat yields. With data from 90 studies using computer modeling, we found that more than 50% of the simulated relative yield change resulted in yield losses when mean temperature change is higher than 2.3 degrees C, or mean precipitation change is null or less, or when CO2 concentration is lower than 395 ppm. A statistical model relating relative yield change to the three considered climatic variables was used to explore a large range of climate change scenarios. Results showed that, in average, the effects of high CO2 concentrations (>640 ppm) outweighed the effects of increasing temperature (up to +2 degrees C) and moderate declines in precipitation (up to 20%), leading to increasing yields. However, these results varied greatly from site to site, likely due to differences in topography, soils and farming practices. These results also do not take into account the effects of pests, diseases and weeds or climate variability, which may act to decrease wheat yields. (C) 2013 Elsevier B.V. All rights reserved.

Conservation agriculture (CA) is often quoted as a beneficial resource-saving technique for dryland agriculture, but its large-scale implementation is frequently hindered by the lack of farmers' acceptance. To date, few studies have investigated the impact of spatial factors, costs and benefits and regional agroecosystem differentiation on adoption of CA. This study, therefore, aims to assess the impact of these factors through a case study in the North Ethiopian Highlands. One hundred eight farmers of 11 villages surrounding an experimental plot were interviewed in order to identify their knowledge and acceptance of the technique. The results show that several spatial factors play a role in CA acceptance. The lack of knowledge on the resource-saving technique proved primarily dependent (R = -0.73) on spatial impedance with the innovation source and on the strength of sociospatial networks. Next, a consumer model showed that perceived costs and benefits seem to balance each other. Finally, some agronomic traditions were identified that are related to the regional agroecosystem, which are not favoring the implementation of zero-tillage practices. Since this study identified acceptance problems related to several spatial and regional factors, future CA adoption schemes must allow better regional differentiation optimized to local contexts and conditions.

Developing models to predict on-site soil erosion and off-site sediment transport at the agricultural watershed scale represent an on-going challenge in research today. This study attempts to simulate the daily discharge and sediment loss using a distributed model that combines surface and sub-surface runoffs in a small hilly watershed (< 1km(2)). The semi-quantitative model, Predict and Localize Erosion and Runoff (PLER), integrates the Manning-Strickler equation to simulate runoff and the Griffith University Erosion System Template equation to simulate soil detachment, sediment storage and soil loss based on a map resolution of 30m x 30m and over a daily time interval. By using a basic input data set and only two calibration coefficients based, respectively, on water velocity and soil detachment, the PLER model is easily applicable to different agricultural scenarios. The results indicate appropriate model performance and a high correlation between measured and predicted data with both Nash-Sutcliffe efficiency (Ef) and correlation coefficient (r(2)) having values>0.9. With the simple input data needs, PLER model is a useful tool for daily runoff and soil erosion modeling in small hilly watersheds in humid tropical areas.

This study presents a Holocene sediment budget for the Valdaine Region, located at the edge of the southern French Pre-Alps. Holocene colluvial and alluvial deposition are quantified based on existing and new field data. Average sediment thickness values were calculated for different landscape units, and available chronological data were used to make a time-differentiated sediment budget. Total Holocene colluvial deposition in the Valdaine (334 km2) amounts 167 × 106m3, while alluvial deposition in the Roubion and Jabron catchments (in total 610 km2, including their catchment upstream the Valdaine) amounts 177 × 106m3. Especially, colluvial deposition is high (0.75 × 106g/m2) compared with other catchments. Three major deposition periods (8500–2000 bc, 700 bc–ad 800 and ad 1200–2000) and two periods of relative hillslope stability with local fluvial incision (2000–700 bc and ad 800–1200) set the framework for a time-differentiated sediment budget. Results show that depositional phases relate to intense land use and hillslope stability and fluvial incision to land abandonment. Catchment averaged colluvial deposition increases from 13 × 10−6m3/m2/yr for 8500–2000 bc to 355 × 10−6m3/m2/yr for ad 1200–2000, while alluvial deposition increases from 16 to 147 × 10−6m3/m2/yr between the same time periods. A relationship with climatic fluctuations was not found because of the limited temporal resolution of the sediment budget. The derived sediment cascade model shows how alluvial sediments change from fine (silt and clay) to coarse (sand and gravel) after ad 1200. This went along with the establishment of a braided river pattern, indicating that the main source of sediment shifted to the mountainous headwaters. Further research including fingerprinting and modeling would be necessary to further understand the sediment budget and to more accurately quantify the different source areas and the export from the catchment.

Erosion is one of the important problems in degradation of agricultural lands and other natural lands. The most dynamic factor in controlling erosion is land cover, and this factor has been anthropogenically manipulated for ages. This study investigates the effect of land use and land cover changes (LULCC) on erosion at Kuseyr Plateau, which is situated in the southernmost part of the eastern Mediterranean basin, Turkey. A geographical information systems-based method using the revised universal soil loss equation (3D) was employed to identify the amount of annual soil loss, erosion risk classes, and distribution generated by LULCC. Landsat satellite images were used to analyze LULCC from 1987 to 2010. The implementations of both land cover and management factors were made possible by satellite image analysis performed throughout the years. The results obtained from the study show that there is a rather severe erosion risk covering as much as 30% of the land within the scope of the study for 1987; this rate corresponds to 22% in 2010. Maximum annual soil loss in the plateau was as high as 59.81 t ha(-1) per year in 1987 and 48.33 t ha(-1) per year in 2010. The average soil losses in the plateau were 6.19 and 5.00 t ha(-1) per year for 1987 and 2010, respectively. The related processes causing erosion from the past to present have slowed down, and reclamation of the land cover (with the intended purpose of decreasing erosion sensitivity) has always been the key factor in this regard. Despite a considerable decrease in severe erosion, as much as 22% of the study area still requires immediate measures in order to reduce soil loss.

The impact of slope aspect on hydrological rainfall and on the magnitude of rill erosion has rarely been studied. The dominant wind direction in Belgium and northern France is the southwest, which brings large amounts of rain with it. We investigated whether this leads to greater rates of rill erosion on the southwestern slopes, due to the greater amount of hydrological precipitation on these slopes. The study was executed on six barren conical spoil heaps, which are excellent study objects to bring the slope aspect in relation with rill erosion. Three indicators for rill erosion (volume of rills, drainage density and mean distance of the head cut of the five uppermost rills till the top of the spoil heap) were associated with four explanatory factors (slope gradient, vegetation density, rock fragment cover and slope aspect). The amount of hydrological rainfall is the greatest on the western and southwestern slopes. As a result, the largest volume of rills was measured on the slopes facing the southwest (96%), which indicates that there is a connection between the slope aspect and the magnitude of rill erosion. On the northeastern (32%) and eastern (36%) slopes the volume of rills is lower due to the effect of rain shadow. The other explanatory factors showed little influence on the magnitude of rill erosion, as the spoil heaps were selected to be similar in as many parameters as possible.

The vector physics of wind-driven rain (WDR) differs from that of wind-free rain, and the interrill soil detachment equations in the Water Erosion Prediction Project (WEPP) model were not originally developed to deal with this phenomenon. This article provides an evaluation of the performance of the interrill component of the WEPP model for WDR events. The interrill delivery rates were measured in the wind tunnel facility of the International Center for Eremology (ICE), Ghent University, Belgium with an experimental setup to study different raindrop impact velocity vectors. Synchronized wind and rain simulations with wind velocities of 6, 10 and 14 m s–1 were applied to a test surface placed on windward and leeward slopes of 7, 15 and 20%. Since both rainfall intensity and raindrop impact velocity varied greatly depending on differences in the horizontal wind velocity under WDRs, the resultant kinetic energy flux (KEr, in J m–2 s–1) was initially used in place of the WEPP model intensity term in order to incorporate the effect of wind on impact velocity and frequency of raindrops. However, our results showed only minor improvement in the model predictions. For all research data, the model Coefficients of Determination (r2) were 0·63 and 0·71, when using the WEPP and the KEr approaches, respectively. Alternately, integrating the angle of rain incidence into the model by vectorally partitioning normal kinetic energy flux (KErn, in J m–2 s–1) from the KEr greatly improved the model's ability to estimate the interrill sediment delivery rates (r2¿=¿0·91). This finding suggested that along with the fall trajectory of wind-driven raindrops with a given frequency, raindrop velocity and direction at the point of impact onto the soil surface provided sufficient physical information to improve WEPP sediment delivery rate predictions under WDR

To assess the inflfl uence of rainfall simulator type and plot dimensions on runoff and erosion, seven small portable rainfall simulators from Freiberg, Tubingen, Trier (all Germany), Valencia, Zaragoza (both Spain), Basel (Switzerland) and Wageningen (the Netherlands) were compared on a prepared bare fallow fifi eld. The experiments were carried out during an international rainfall simulator workshop, organized at Trier University (Germany) from 30th of June to 1st of July 2011.The tested rainfall simulators differ in design, rainfall intensities, rain spectra, etc. and represent most of the devices which have been used over the last decade in Europe. The plots for the different rainfall simulators were selected as similar as possible concerning soil physical and chemical properties, aspect and inclination and were chosen to be placed side by side in horizontal direction. Test procedure was standardized in order to examine the inflfl uence of the rainfall simulator andplot dimension only. The results show a clear and consistent relationship in runoff, erosion and infifi ltration behaviour of the different used rainfall simulators. With all the devices total soil loss is measurable, but different plot sizes, intensities and kinetic energies of the simulated rainfall caused differences in soil loss and runoff quantities per unit of area. Regarding course characteristics over runs, similarities could be observed especially in runoff behaviour. The rainfall simulators (> 1 m² plot size) are able to reproduce infifi ltration and interrillerosion processes. With an increase of plot size (≥ 1 m²), rill-erosion will be also reflfl ected. Therefore it can be concluded that up to a certain plot size, the results of the different simulators are comparable and depend in their magnitude on the properties of the applied rainfall. The increase in process complexity with increasing plot size shows, that the scale of the simulation is one of the most important parameters to be taken intoaccount when comparing values of erosion and runoff.

Soil loss and sediment transport in Mediterranean areas are driven by complex non-linear processes which have been only partially understood. Distributed models can be very helpful tools for understanding the catchment-scale phenomena which lead to soil erosion and sediment transport. In this study, a modelling approach is proposed to reproduce and evaluate erosion and sediment yield processes in a Mediterranean catchment (Rambla del Poyo, Valencia, Spain). Due to the lack of sediment transport records for model calibration and validation, a detailed description of the alluvial stratigraphy infilling a check dam that drains a 12.9 km2 sub-catchment was used as indirect information of sediment yield data. These dam infill sediments showed evidences of at least 15 depositional events (floods) over the time period 1990-2009. The TETIS model, a distributed conceptual hydrological and sediment model, was coupled to the Sediment Trap Efficiency for Small Ponds (STEP) model for reproducing reservoir retention, and it was calibrated and validated using the sedimentation volume estimated for the depositional units associated with discrete runoff events. The results show relatively low net erosion rates compared to other Mediterranean catchments (0.136 Mg ha -1 yr-1), probably due to the extensive outcrops of limestone bedrock, thin soils and rather homogeneous vegetation cover. The simulated sediment production and transport rates offer model satisfactory results, further supported by in-site palaeohydrological evidences and spatial validation using additional check dams, showing the great potential of the presented data assimilation methodology for the quantitative analysis of sediment dynamics in ungauged Mediterranean basins. © 2013 Author(s).

Scaling-up sediment transport has been problematic because most sediment loss models (e.g., the Universal Soil Loss Equation) are developed using data from small plots where runoff is generated by infiltration excess. However, in most watersheds, runoff is produced by saturation excess processes. In this article, we improve an earlier saturation excess erosion model that was only tested on a limited basis, in which runoff and erosion originated from periodically saturated and severely degraded areas, and apply it to five watersheds over a wider geographical area. The erosion model is based on a semi-distributed hydrology model that calculates saturation excess runoff, interflow, and baseflow. In the development of the erosion model, a linear relationship between sediment concentration and velocity in surface runoff is assumed. Baseflow and interflow are sediment free. Initially during the rainy season in Ethiopia, when the fields are being plowed, the sediment concentration in the river is limited by the ability of the surface runoff to move sediment. Later in the season, the sediment concentration becomes limited by the availability of sediment. To show the general applicability of the Saturation Excess Erosion Model (SEEModel), the model was tested for watersheds located 10,000 km apart, in the U. S. and in Ethiopia. In the Ethiopian highlands, we simulated the 1.1 km(2) Anjeni watershed, the 4.8 km(2) Andit Tid watershed, the 4.0 km(2) Enkulal watershed, and the 174,000 km(2) Blue Nile basin. In the Catskill Mountains in New York State, the sediment concentrations were simulated in the 493 km(2) upper Esopus Creek watershed. Discharge and sediment concentration averaged over 1 to 10 days were well simulated over the range of scales with comparable parameter sets. The Nash-Sutcliffe efficiency (NSE) values for the validation runs for the stream discharge were between 0.77 and 0.92. Sediment concentrations had NSE values ranging from 0.56 to 0.86 using only four calibrated sediment parameters together with the subsurface and surface runoff discharges calculated by the hydrology model. The model results suggest that correctly predicting both surface runoff and subsurface flow is an important step in simulating sediment concentrations. International Foundation for Science (IFS) Higher Education for Development (HED) USDA International Science and Education (ISE) program

District Swat is part of the high mountain Hindu-Kush Himalayan region of Pakistan. Documentation and analysis of land use change in this region is challenging due to very disparate accounts of the state of forest resources and limited accessible data. Such analysis is, however, important due to concerns over the degradation of forest land leading to deterioration of the protection of water catchments and exposure of highly erodible soils. Furthermore, the area is identified as hotspot for biodiversity loss. The aim of this paper is to identify geophysical and geographical factors related to land use change and model how these relationships vary across the district. For three selected zones across the elevation gradient of the district, we analyse land use change by studying land use maps for the years 1968, 1990 and 2007. In the high-altitude zone, the forest area decreased by 30.5 %, a third of which was caused by agricultural expansion. In the mid-elevation zone, agriculture expanded by 70.3 % and forests decreased by 49.7 %. In the lower altitudes, agriculture expansion was 129.9 % consuming 31.7 % of the forest area over the forty-year time period. Annual deforestation rates observed were 0.80, 1.28 and 1.86 % in high, mid and low altitudes, respectively. In the high-altitude ecosystems, accessibility (distance to nearest road and city) had no significant role in agriculture expansion; rather land use change appears significantly related to geophysical factors such as slope, aspect and altitude. In the low-elevation zone, accessibility was the factor showing the closest association with agriculture expansion and abandonment. The analysis illustrates that land use change processes vary quite considerably between different altitudinal and vegetation cover zones of the same district and that environmental constraints and stage of economic development provide important contextual information.

An obvious timescale gap exists between a single storm event and long term landscape development. In this study the event- and physically based OpenLISEM soil erosion model was compared to the landscape evolution model LAPSUS, deliberately extending and shortening the timescales for which each model was developed. Calibration of OpenLISEM using average erosion rates derived from long-term simulations with LAPSUS and, vice versa, calibration of LAPSUS on event-scale did not give satisfactory results, suggesting that the gap between the different timescales of both models is too large to be bridged directly. However, calibration of LAPSUS on annual basis using the summed OpenLISEM erosion and deposition values for each year resulted in a good reproduction of these values by LAPSUS. Thus, when keeping to the timescale that the model was originally intended for, but calibrating the model using simulation results from the event-based model, short-term variability could successfully be introduced in longer-term modelling of landscape development. Subsequently, the erosion effects of rainfall variability, climate and land use change were explored on a centennial timescale. Results show non-linear behaviour between rainfall input and simulated net erosion. Simulated net erosion for increased rainfall erosivity was compared to rainfall variability, showing that mean annual net erosion of up to 15% increased erosivity is not significantly different from annual mean net erosion of the original simulations. Single events must be of very high magnitude and/or frequency to leave a signal in the landscape that is beyond the scope of natural rainfall variability. Scenarios of human impact show that land use changes can have a potentially larger effect on erosion dynamics than climate variability and change. This is the first time that an event-based erosion model and a landscape evolution model were calibrated for the same area and compared in terms of erosion and deposition dynamics.

Understanding historical and present gully development is essential when addressing the causes and consequences of land degradation, especially in vulnerable dryland environments. For Northern Ethiopia, several studies exist on the severity of gully erosion, yet few have quantified gully development. In this study, gully network and volume development were quantified over the period 1963–2010 for an area of 123 km2, representing the regional variability in environmental characteristics. Gully networks were mapped from small-scale aerial photographs and high-resolution satellite images. For the latter, visualizing Google Earth images in 3D proved to be very suitable to investigate gully erosion. From the changes in networks and volumes over the period 1963–2010, the occurrence of one cut-and-fill cycle is apparent. From a largely low-dynamic gully system in the 1960s, network expansion and increased erosion rates in the 1980s and 1990s caused the drainage density and volume to peak in 1994. The average gully density (Dtotal) was then 2.52 km km− 2 and the area-specific gully volume (Va) 60 × 103 m3 km− 2. This coincides with soil losses by gully erosion (SLg) of 17.6 t ha− 1 y− 1 over the period 1963–1994. By 2010, improved land management and the region-wide implementation of soil and water conservation measures caused 25% of the gully network to stabilize, resulting in a net infilling of the gully channels over the period 1994–2010. The study validates previous findings that land degradation by gullying was indeed severe in Northern Ethiopia in the second half of the 20th century, but also shows that when proper land management is applied, a gully can be transformed into a linear oasis, which increases the resistance of gullies to further erosion.

Agriculture has a large impact on the environment and retailers increasingly stimulate their suppliers to reduce the environmental impact of agricultural production. The environmental impact resulting from producing a commodity can be measured with a life cycle analysis (LCA) but performing an LCA is costly and time-consuming. In the first paper of this series a practical and general method to identify hotspot areas in crop production on a global scale was developed. The method was implemented for potatoes. The objective of the work reported here was to evaluate the tool and to identify improvement opportunities for each of seven indicators: yield, erosion risk, nitrogen surplus, depletion of water reserves, biocide use, carbon footprint, and impact on biodiversity. The tool produces realistic outputs that can be used to target improvement efforts and thus improves the use efficiency of limited resources. The tool can be expanded to produce similar results for other crops; methods to improve the resolution of the tool are discussed.

A conceptual model of an instantaneous unit sediment graph (IUSG) has been developed for sediment transport prediction in the arid regions. It involved routing of the sediment through a cascade of identical linear reservoirs. The sediment graphs generated by convolution of IUSG compared well with the observed values for four representative arid sub-basins of the Luni River in India. The sediment supply is related to the effective precipitation and to transmission losses in the upland and channel phases, respectively, and the model parameters are estimated from the observed events. The model can be applied to ungauged flow events through parameterization. (C) 1996 Academic Press Limited

This study offers an approach to estimate the rainfall kinetic energy (KE) by rain intensity (R) and radar reflectivity factor (Z) separately or jointly on the basis of a one- or two-moment scaled raindrop size distribution (DSD) formulation, which contains (1) R and/or Z observations and (2) the dimensionless probability density function (pdf) of a scaled raindrop diameter. The key point is to explain all variability of the DSD by the evolution of the explaining moments (R and Z); hence the pdf is considered as constant. A robust method is proposed to estimate the climatological values of the parameters with a 28 month DSD data set collected in the Cévennes-Vivarais region of France. Three relationships (KE-R, KE-Z, and KE-RZ), which link the observations (R and/or Z) to rainfall kinetic energy (KE), are established. As expected, the assessment using the disdrometer data indicates that (1) because of the proximity of the moment orders, the KE-Z relationship exhibits less variability than the KE-R relationship and (2) the combination of R and Z yields a significant improvement of the estimation of KE compared to the single-moment formulations. Subsequently, a first attempt to spatialize the kinetic energy using radar and rain gauge measurements is presented for a convective event, showing a promising potential for erosion process studies. Different from the application with the disdrometer data, the performance of the KE-Z relationship degrades compared to the KE-R relationship as a result of a bias and/or the sampling characteristics of the radar data

Despite many efforts over the last decades to understand rill erosion processes, they remain unclear. This paper presents the results of rill experiments accomplished in Andalusia in September 2008 using a novel experimental set up. 72 L of water are introduced with an intensity of 9 L min(-1) into a rill. Rill cross sections, slope values, flow velocities and sediment concentrations were measured and these values were used to calculate sediment detachment and transport. Each experiment was repeated once within 15 min. With this new experimental setup it is possible to calculate several hydraulic parameters like hydraulic radius, wetted perimeter, flow cross section, transport rate and transport capacity which are usually estimated from coarse flow and rill parameters. In rill experiments, four different natural rills were flooded with the same experimental setup. Several processes like transport of loose material, erosion, bank failure and knickpoint retreat and the runoff effectiveness showed different and variable intensities. The sediment concentrations ranged between 5.2 and 438 g L-1. most cases, detachment rates are close to the transport capacity and, in some cases, the transport capacity is even exceeded. This can be explained by the occurrence of different erosion processes within a rill (e.g. detachment, bank failure, and headcut retreat) which are not all explained by the given equations. The results suggest that the existing soil erosion equations based on shear forces exerted by the flowing water are not able to describe rill erosion processes satisfactory. Too many different processes with a high spatial and temporal variability are responsible for rill development. (C) 2010 Elsevier B.V. All rights reserved.

This study offers an approach to estimate the rainfall kinetic energy (KE) by rain intensity (R) and radar reflectivity factor (Z) separately or jointly on the basis of a one- or two-moment scaled raindrop size distribution (DSD) formulation, which contains (1) R and/or Z observations and (2) the dimensionless probability density function (pdf) of a scaled raindrop diameter. The key point is to explain all variability of the DSD by the evolution of the explaining moments (R and Z); hence the pdf is considered as constant. A robust method is proposed to estimate the climatological values of the parameters with a 28 month DSD data set collected in the Cévennes-Vivarais region of France. Three relationships (KE-R, KE-Z, and KE-RZ), which link the observations (R and/or Z) to rainfall kinetic energy (KE), are established. As expected, the assessment using the disdrometer data indicates that (1) because of the proximity of the moment orders, the KE-Z relationship exhibits less variability than the KE-R relationship and (2) the combination of R and Z yields a significant improvement of the estimation of KE compared to the single-moment formulations. Subsequently, a first attempt to spatialize the kinetic energy using radar and rain gauge measurements is presented for a convective event, showing a promising potential for erosion process studies. Different from the application with the disdrometer data, the performance of the KE-Z relationship degrades compared to the KE-R relationship as a result of a bias and/or the sampling characteristics of the radar data

Landscape evolution models (LEMs) quantitatively simulate processes of sedimentation and erosion on millennial timescales. An important aspect of human impact on erosion is sediment redistribution due to agriculture, referred to herein as tillage erosion. In this study we aim to analyse the potential contribution of tillage erosion to landscape development using LEM LAPSUS. The model is calibrated separately for a water erosion process (i) without tillage and (ii) with tillage. The model is applied to the ~250¿km2 Torrealvilla case study catchment, SE Spain. We were able to simulate alternating sequences of incision and aggradation, that are important on longer (millennial) timescales. Generally, model results show that tillage erosion adds to deposition in the lower floodplain area, but neither water erosion alone nor water with tillage erosion together could exactly reproduce the observed amounts of erosion and sedimentation for the case study area. In addition, scale effects are apparent. On hillslopes, tillage may contribute importantly to erosion and may fill local depressions. If assessed on the catchment scale, sediments from tillage erosion eventually reach the lower floodplain area where they contribute to deposition. However, water erosion was observed in the model simulations to be the most important process on the catchment scale. This is the first time that tillage erosion has been explicitly included in a landscape evolution model at a millennial timescale and large catchment scale.

peer-reviewed Throughout the European Union (EU), agricultural soils with high phosphorus (P) status due to surplus fertiliser input have been identifi ed as a landscape pressure impacting on water quality. In Republic of Ireland, approximately 80% of agricultural land is devoted to grass, 11% to rough grazing, and 9% to arable cereal and crop production. Consequently, the majority of erosion research has focused on quantifying nutrient and sediment losses from grassland. Tillage soils are, however, more susceptible to erosion than grassland soils and, in general, have higher levels of soil P. This paper reviews the current state of research and the regulatory regime relating to diffuse P and sediment loss for tillage soils. It identifi es the key threats to soil quality associated with cultivated soils, and proposes the targeting and remediation of critical source areas for effective mitigation of P losses from tillage soils. A multiscaled approach is recommended, in which catchment and field-scale monitoring is complemented with controlled laboratory and small plot-scale rainfall simulation experiments to identify areas where P loss and soil erosion are at critical levels and may pose a threat to water quality. Catchment scale research will help to link critical source areas of sediment and P loss with hydrological pathways to surface waters in the catchment area. These areas can then be targeted for remediation in the river basin management plans. Teagasc Walsh Fellowship Programme

Due to overgrazing and agricultural intensification, gully erosion severely affects sub-Saharan countries; however, insufficient quantitative studies exist for this part of the world. This paper presents data on gully head retreat rates in Northern Ethiopia and relates these rates to gully and environmental characteristics. The monitoring of headcuts over one rainy season (2010) revealed that present-day retreat rates are low, with average annual linear (Rl), areal (Ra) and volumetric (Ve) retreat rates of 0.34 m y− 1, 1.70 m2 y− 1 and 5.2 m3 y− 1, respectively. These results express the positive effects of recent soil and water conservation practices on gully stabilization. Significantly higher values of Rl (up to 1.93 m y− 1) occurred in the Vertisol areas affected by soil piping. When considering the medium- to long time scale (1–47 years) using archival terrestrial (and aerial) photographs, headcut retreat rates proved to be significantly higher than those in the short term. The averages for Rl, Ra and Ve are 3.8 m y− 1, 31.5 m2 y− 1 and 47.7 m3 y− 1, respectively. Retreat rates are up to 10 times higher after road construction. For the medium to long term, headcut retreat rates were positively related to the catchment area (A). A power relationship that best describes the relation between Ve and A is Ve = 0.53 A0.31 (r2 = 0.27, n = 18). Compared to other areas worldwide, regressive erosion has been rapid in Ethiopia as a result of the degraded and steep landscape combined with erosive rains and the occurrence of Vertisols. In Vertisols, headcut retreat is controlled by soil piping. Because no adequate techniques exist to control gully initiation and development in Vertisols, alternative techniques should be developed that deactivate soil pipes.

Precise estimation of mean flow velocity (U-mean) is imperative for accurate prediction of hydrographs and sediment yield. For overland flow, U-mean is normally estimated by multiplying the dye or salt based velocity measurement with a correction factor (alpha). A wide range of correction factors is available in the literature, all of which were derived under different experimental conditions. The selection of a suitable a has become a main challenge for accurate mean flow calculations. This study aimed to assess the variability of a with grain size (D-50) and slope (S), and to evaluate the dependency of U-mean on flow rate (Q), D-50 and S by regression analysis. Flume experiments were performed at Q varying from 33 to 1033 x 10(-6) m(3) s(-1), S ranging from 3 degrees to 10 degrees, and D-50 ranging from 0.233 to 1.022 mm. Flow velocities were measured directly with the dye tracing technique (U-dye), and derived indirectly from flow depth measurements (U-depth). The Udepth measurements were considered as U-mean. The derived alpha (U-depth/U-dye) values did not remain constant with sediment size and increase significantly with the increase of D-50. The mean alpha values for 0.230, 0.536, 0.719 and 1.022 mm sands were 0.44, 0.77, 0.82 and 0.82, respectively. Hence, due to the substantial variation of alpha with D-50, no absolute alpha value is applicable to all hydraulic and sedimentary conditions. However, mean alpha values for 0.230, 0.536 and 0.719 mm sands were found comparable with alpha values available in the literature for similar grain sizes. The influence of Q S. and D-50 on U-mean was studied by regression analysis. Regression analysis depicted the significant influence of Q and D-50 on U-mean. while the effect of slope was found to be non-significant. Comparison of the derived regression equation with five literature datasets showed that the model can predict mean flow velocities in overland flow at a reasonable accuracy as long as the mean velocity is below 0.4 m s(-1). At higher velocities the error becomes unacceptably large.

Lake Elton is located east of the Volga River in Russia and covers an area of 155¿km2. The hydrological system of the Lake and its surroundings are extremely vulnerable to climate change and human interference, but available local and regional information is sparse. Utilising climate data from 1987 to 2009 and surface albedo readings from the MODerate resolution Imaging Spectroradiometer satellite since 2000, this study analyses Lake degradation processes since 2005. Lake surface albedo analysis indicates that during the past 6¿years, lake albedo has increased dramatically from average peak values of 0·14 to 0·40. In addition, air temperature has increased by 2¿°C, and annual precipitation has decreased by 40 per cent. Moreover, human intervention in the area has increased environmental pressure on the Lake, causing a reduction of runoff inflow because of water capture, use of check-dams and water-harvesting systems. The results of the study show that, under current conditions, the Lake surface albedo is likely to remain high as compared with previous observations. The current trend implies an average 2 per cent per year increase in future annual albedo, with a maximum possible increase of 4 per cent up to a steady state of salt-crust albedo values

this article the global potential of energy crop production on degraded lands was estimated using detailed, spatially explicit data about the area, type and extent of degradation derived from the Global Assessment of Land Degradation Dataset, and by combining this dataset with various spatially explicit data sets. Next, an estimate was made of the possible yield of perennial energy crops on the degraded areas as a function of the type and degree of degradation. Lightly degraded areas were not included, as these areas might be suitable for conventional food production. The total global potential energy production on degraded lands was assessed to be slightly above 150 and 190 EJ yr -1, for grassy and woody energy crops, respectively. Most of this potential, however, is on areas currently classified as forest, cropland or pastoral land, leaving a potential of around 25 and 32 EJ yr -1 on other land cover categories. Most of the potential energy crop production on degraded land is located in developing regions. China has a total potential of 30 EJ yr -1, of which 4 EJ yr -1 from areas classified as other land. Also USA, Brazil, West Africa, East Africa, Russia and India have substantial potentials of 12-18 EJ yr -1, with up to 30% of the potential from areas classified as other land.

Although water erosion is the principle agent responsible for soil degradation, field data on the impacts of erosion, due to high operational costs and measurement difficulties, are scarce, especially in semiarid regions. In this context, the aim of this study was to evaluate runoff and soil and nutrient losses in uncultivated areas in the semiarid region of the state of Ceará in Brazil. The experiment was conducted in a 20 m² erosion plot that was uncultivated and populated with herbaceous plants. Data were collected during the rainy season from January to May 2009. Monthly water losses from overland flow ranged from 3.4 to 168.9 mm, representing 1.8 to 42.3% of the total monthly rainfall for January and April, respectively. Soil loss from erosion totaled 2,166.6 kg ha-1. In February, soil losses were 834.3 kg ha-1, corresponding to 38.5% of the total value. The rainfall erosivity index (EI30) was 5,716.4 MJ mm ha-1 h-1. The observed high variability of soil losses in individual events was influenced mainly by the antecedent soil water content. Although this study used only one year of observations, the findings are important for land use planning, especially in the semiarid region of Brazil, where datasets are scarce. Embora a erosão hídrica seja a principal agente no empobrecimento dos solos e na contaminação dos recursos hídricos, poucos são as mensurações efetuadas em campo. A baixa disponibilidade de dados obtidos in loco é decorrente do elevado custo e das dificuldades na efetivação destas mensurações, em especial nas regiões semiáridas. Neste sentido, o presente estudo teve como objetivos investigar a ação das erosividades das chuvas sobre o escoamento superficial, bem como as perdas de solo e nutrientes em áreas não cultivadas do semiárido cearense. O experimento foi conduzido em uma parcela de erosão (20 m²) sob condições de áreas não cultivadas com cobertura vegetal composta por extrato herbáceo. Neste estudo foram investigados 37 eventos registrados no período chuvoso de 2009 (janeiro/maio). O acumulado mensal do escoamento superficial variou de 3,4 a 168,9 mm, correspondendo a 1,8 e 42,3% da precipitação total mensal, para janeiro e abril, respectivamente. As perdas de solo para todo o período estudado foram de 2.166,6 kg ha-1, com destaque para o mês de fevereiro com perdas de 834,3 kg ha-1, correspondendo a 38,5% do valor total. O índice de erosividade (EI30) da chuva foi de 5.716,4 MJ mm ha-1 h-1./ A alta variabilidade nos valores de perda de solo por eventos isolados foi influenciada principalmente pela umidade antecedente do solo. Os resultados obtidos nesse trabalho, embora iniciais, são valiosos para a gestão e planejamento adequado de uso da terra, principalmente em regiões semiáridas onde essas informações são mais escassas.

† Background and Aims Vegetation has long been recognized to protect the soil from erosion. Understanding species differences in root morphology and functional traits is an important step to assess which species and species mixtures may provide erosion control. Furthermore, extending classification of plant functional types towards root traits may be a useful procedure in understanding important root functions. † Methods In this study, pioneer data on traits of alpine plant species, i.e. plant height and shoot biomass, root depth, horizontal root spreading, root length, diameter, tensile strength, plant age and root biomass, from a disturbed site in the Swiss Alps are presented. The applicability of three classifications of plant functional types (PFTs), i.e. life form, growth form and root type, was examined for above- and below-ground plant traits. † Key Results Plant traits differed considerably among species even of the same life form, e.g. in the case of total root length by more than two orders of magnitude. Within the same root diameter, species differed significantly in tensile strength: some species (Geum reptans and Luzula spicata) had roots more than twice as strong as those of other species. Species of different life forms provided different root functions (e.g. root depth and horizontal root spreading) that may be important for soil physical processes. All classifications of PFTs were helpful to categorize plant traits; however, the PFTs according to root type explained total root length far better than the other PFTs. † Conclusions The results of the study illustrate the remarkable differences between root traits of alpine plants, some of which cannot be assessed from simple morphological inspection, e.g. tensile strength. PFT classification based on root traits seems useful to categorize plant traits, even though some patterns are better explained at the individual species level.

Soil erosion is often regarded as one of the main processes of desertification. This has led to the use of various desertification indicators that are related to soil erosion. Most of these indicators focus, however, on small spatial units, while little attention has been given to the amount of sediment exported at the catchment scale. Such a small spatial unit approach neglects the transfer of sediment through catchments as well as the scale-dependency of erosion processes. Furthermore, this approach does not consider important off-site impacts of soil erosion, such as sediment deposition in reservoirs, flooding as well as ecological impacts. This study aims to illustrate the importance of also considering catchment sediment yield (SY, t km(-2) y(-1)) in desertification assessment studies. Based on recently established databases of SY and soil loss rates in Europe and examples from previous studies, we illustrate that soil erosion rates at the plot scale are not representative for catchment SY, as they are often several orders of magnitude smaller. Also, the erosion response of catchments to changes in land use or climate often differs strongly from responses to those changes at the plot scale. We further discuss several of the impacts of SY and their link with desertification: i.e. the sedimentation of reservoirs, problems related to flooding, catchment hydrology, export of nutrients and ecological implications. Using earlier established criteria we evaluate the potential for using catchment SY as a desertification indicator and conclude that this could give an important added value to desertification studies. SY, used in combination with other indicators, allows the identification of other sediment sources than those considered at the plot scale and can reflect the results of desertification processes over longer time periods than periods over which assessments at the plot scale have been made. We argue therefore, that SY is a strong complementary indicator of desertification providing valuable information on the catchment response to changes in drivers of desertification.

This study compares three landscape evolution models and their ability to correctly simulate measured 2500¿year landscape evolution in two small catchments in the Belgian loess belt. WATEM LT and LAPSUS both model tillage and water erosion and deposition and have detachment-limited descriptions for water erosion and deposition. Equations in LAPSUS are more mechanistic than those in WATEM LT. WATEM LTT resembles WATEM LT, but is a transport-limited model. All three models are DEM-based. Calibration and validation simulations were performed forward in time on (1D) transects for four spatial resolutions, and backward in time for (2D) catchments at 20¿m resolution. For transects, model outputs were compared with discretized observations of transect shape. For catchments, outputs were compared with point observations of palaeo-altitude, averaged over landscape element classes. For transects, the three models performed well, resulting in model efficiency factors of 0.92 to 0.99 for calibration and 0.62 to 0.96 for validation. However, for catchments, simulations showed that the transport-limited WATEM LTT model could not realistically simulate long-term landscape evolution. Performance of WATEM LT and LAPSUS at catchment scale was similar to that on transects, although LAPSUS has problems with backward calculation. Tests demonstrate that a transport-limited approach cannot be used to model long-term landscape evolution in the Belgian loess belt, which is in agreement with theoretical and empirical understanding of soil erosion processes in this environment. The difference in performance between transport-limited and detachment-limited models is clear only when the models are evaluated in a 2D catchment. The lack of such distinction when models were applied in a 1D transect highlights the importance of evaluating landscape evolution models in a 2D setting so that effects of flow convergence/divergence can be accounted for. Copyright © 2011 John Wiley & Sons, Ltd

Increasing nitrogen (N) and phosphorus (P) inputs have greatly contributed to the increasing food production in China during the last decades, but have also increased N and P losses to the environment. The pathways and magnitude of these losses are not well quantified. Here, we report on N and P use efficiencies and losses at a national scale in 2005, using the model NUFER (NUtrient flows in Food chains, Environment and Resources use). Total amount of "new" N imported to the food chain was 48.8 Tg in 2005. Only 4.4.Tg reached households as food. Average N use efficiencies in crop production, animal production, and the whole food chain were 26, 11, and 9%, respectively. Most of the imported N was lost to the environment, that is, 23 Tg N to atmosphere, as ammonia (57%), nitrous oxide (2%), dinitrogen (33%), and nitrogen oxides (8%), and 20 Tg to waters. The total P input into the food chain was 7.8 Tg. The average P use efficiencies in crop production, animal production, and the whole food chain were 36, 5, and 7%, respectively. This is the first comprehensive overview of N and P balances, losses, and use efficiencies of the food chain in China. It shows that the N and P costs of food are high (for N 11 kg kg(-1), for P 13 kg kg(-1)). Key measures for lowering the N and P costs of food production are (i) increasing crop and animal production, (ii) balanced fertilization, and (iii) improved manure management.

The Yellow River basin contributes approximately 6% of the sediment load from all river systems globally, and the annual runoff directly supports 12% of the Chinese population. As a result, describing and understanding recent variations of water discharge and sediment load under global change scenarios are of considerable importance. The present study considers the annual hydrologic series of the water discharge and sediment load of the Yellow River basin obtained from 15 gauging stations (10 mainstream, 5 tributaries). The Mann-Kendall test method was adopted to detect both gradual and abrupt change of hydrological series since the 1950s. With the exception of the area draining to the Upper Tangnaihai station, results indicate that both water discharge and sediment load have decreased significantly (p

International audience; The applicability of conservation agriculture (CA) in sub-Saharan Africa (SSA) is poorly documented. In the ''Nord'' and ''Extre ˆme-Nord'' provinces of Cameroon, in a 2-year rotation between a cereal (maize or sorghum) and cotton, conventional techniques were compared with CA. The study was conducted from 2001 to 2006 in 662 plots in 243 farmers' fields. Cereal treatments compared were conventional management techniques and CA consisting in the production of mulch using cover crops (Brachiaria ruziziensis, Crotalaria retusa, Dolichos lablab, Mucuna pruriens, Vigna unguiculata) intercropped within the cereal. In the ''Extre ˆme-Nord'' province up to 9.7 t ha1 of vegetative biomass was produced in the CA plots with sorghum and cover crops against up to 4.8 t ha1 for sorghum alone in conventional plots. In the ''Nord'' province maize + cover crops produced up to 5.2 t ha1 of biomass against up to 2.5 t ha1 for maize alone. In both provinces, the cereal grain yields were equivalent or higher in CA compared to conventional plots. In 18 fields of the ''Extre ˆme-Nord'' province the mulch remaining the year after sorghum + B. ruziziensis is mainly comprised between 3 t ha1 and 5 t ha1. Cotton treatments compared were T (tillage), NT (no tillage), and NTM (no tillage with mulch). In both provinces these treatments differed in soil cover, number of localized herbicide sprays used, ridging, and amount of nitrogen fertilizer used. In the ''Extre the date of the first weeding. In the ''Extre ˆme-Nord'' province treatments differed also for the number of weeding and ˆme-Nord'' province cotton yieldswere 12% lower for T and 24% lower for NT than for NTM. Cotton yields were regressed on crop husbandry indicators and used inputs. After a manual backward removal in amultiple linear regression respectively no parameters were found to significantly influence yield for T, only one parameter for NT, the number of herbicide sprays used at sowing, and three parameters for NTM: difference between heavy clay and silty loam, application of NPK fertilizer, sowing date. In the ''Nord'' province no difference in cotton yield was observed between T, NT and NTM. The flowering period was longer for NTM vs NT in the ''Extre ˆme-Nord'' and the ''Nord'' provinces andNTM vs T in the ''Nord'' province, respectively 13, 9 and 8 days. Although we show that CA techniques can have benefits at field level, further studies are needed to assess their suitability at farm and village levels.

A vast area (more than 100 000 ha) of forest, shrubs and agricultural land burned on the Peloponnese peninsula in Greece during the 2007 summer. Three pre- and post-fire differenced Landsat Thematic Mapper (TM)-derived spectral indices were correlated with field data of burn severity for these devastating fires. These spectral indices were the Normalised Difference Vegetation Index (NDVI), the Normalised Difference Moisture Index (NDMI) and the Normalised Burn Ratio (NBR). The field data consist of 160 Geo Composite Burn Index (GeoCBI) plots. In addition, indices were evaluated in terms of optimality. The optimality statistic is a measure for the index’s sensitivity to fire-induced vegetation depletion. Results show that the GeoCBI–dNBR (differenced NBR) approach yields a moderately high R2 = 0.65 whereas the correlation between field data and the differenced NDMI (dNDMI) and the differenced NDVI (dNDVI) was clearly lower (respectively R2 = 0.50 and R2 = 0.46). The dNBR also outperformed the dNDMI and dNDVI in terms of optimality. The resulting median dNBR optimality equalled 0.51 whereas the median dNDMI and dNDVI optimality values were respectively 0.50 and 0.40 (differences significant for P

This study presents a Holocene sediment budget for the Nethen catchment, a typical river catchment (55 km2) in the Belgian loess belt. Soil erosion and hillslope sediment storage are quantified by extrapolating detailed data obtained from soil profile truncation studies in three representative zero-order sub catchments. Floodplain sediment storage is estimated by augerings along several transects across the main river and some of its tributaries. The sediment budget shows that ca. 38% of the soil eroded during the Holocene is redeposited as colluvium on hillslopes and in dry valley bottoms. Another 23% of the eroded sediment is now stored as alluvium in the floodplain. The remaining 39% or 21×106 Mg is exported from the catchment. Dating of both colluvial and alluvial sediment deposits reveals that sediment dynamics between the hillslopes, the dry valley bottoms and the floodplain behave highly non-linearly. Before ~500 BC, sediment delivery from the hillslopes to the river channels was near maximum. However, since the onset of significant agriculture in the Late Bronze Age–Early Iron Age, increased rates of soil erosion are only reflected in the colluvium, but not in the floodplain, resulting in very low hillslope sediment delivery ratios. From the Medieval period onwards, soil erosion increased even further, mainly as a result of a further increase in agricultural land use, but now also accelerated floodplain sedimentation took place due to an improved slope-channel coupling and the management of floodplains. ispartof: Geomorphology vol:108 issue:1-2 pages:24-34 status: published

ispartof: Catena vol:77 issue:2 pages:77-80 status: published