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Abstract
Abstract. Soil erosion and sediment yield are strongly affected by land use/land cover (LULC). Spatially distributed erosion models are of great interest to assess the expected effect of LULC changes on soil erosion and sediment yield. However, they can only be applied if spatially distributed data is available for their calibration. In this study the soil erosion and sediment delivery model WATEM/SEDEM was applied to a small (2.84 km2) experimental catchment in the Central Spanish Pyrenees. Model calibration was performed based on a dataset of soil redistribution rates derived from point 137Cs inventories, allowing capture differences per land use in the main model parameters. Model calibration showed a good convergence to a global optimum in the parameter space, which was not possible to attain if only external (not spatially distributed) sediment yield data were available. Validation of the model results against seven years of recorded sediment yield at the catchment outlet was satisfactory. Two LULC scenarios were then modeled to reproduce land use at the beginning of the twentieth century and a hypothetic future scenario, and to compare the simulation results to the current LULC situation. The results show a reduction of about one order of magnitude in gross erosion (3180 to 350 Mg yr−1) and sediment delivery (11.2 to 1.2 Mg yr−1 ha−1) during the last decades as a result of the abandonment of traditional land uses (mostly agriculture) and subsequent vegetation recolonization. The simulation also allowed assessing differences in the sediment sources and sinks within the catchment.
Highlights
According to estimations one sixth of the surface land is affected by accelerated water erosion (Schroter et al, 2005)
For each combination of ktcmax and ktcmin, a soil erosion map was obtained in terms of net soil redistribution (Mg ha−1 yr−1), allowing comparison of the point 137Cs soil redistribution estimates with the model simulations for the 5 × 5 m grid cell corresponding to the location of the 137Cs measurements
Calibration using 137Cs data was very successful, since it was possible to determine a single combination of the ktc parameters that provided a good fit to the observed soil redistribution rates within the catchment
Summary
According to estimations one sixth of the surface land is affected by accelerated water erosion (Schroter et al, 2005). Apart from the at-site problems related to loss of fertile land, sediment yield to the stream network poses problems for hydraulic infrastructures such as reservoirs, and for the preservation of certain fluvial ecosystems. Mountain regions, where the energy relief contributes to increase soil erosion and sediment redistribution rates are among the areas at risk. The effects of LULC change on soil erosion and sediment transport have raised the attention of transnational authorities (e.g. UN, 1994; EC, 2002; COST634, 2005). Many studies have demonstrated that historical LULC change has affected the sediment yield in drainage basins throughout the World (e.g. Dearing, 1992; Piegay et al, 2004; Cosandey et al, 2005; Gyozo et al, 2005)
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