Estimating erosion rates using 137Cs measurements and WATEM/SEDEM in a Mediterranean cultivated field

The loss of fertile topsoil is one of the principal soil degradation problems in agricultural landscapes worldwide. Mediterranean agroecosystems are particularly threatened to soil degradation because of the climate, a higher sensitivity to soil erosion and the intensification of human activities and agricultural practices during centuries. The severity of this problem and the expected increasing risk of soil erosion in Mediterranean cultivated landscapes as a consequence of climate change have generated a demand for estimations of soil redistribution rates and soil loss monitoring. In this study, a representative cultivated field of mountain Mediterranean agroecosystems was selected to estimate Cs-137 derived soil redistribution rates using a Cs-137 mass balance model. Besides numeric simulation was performed using the WATEM/SEDEM model to estimate spatially-distributed soil redistribution rates. A detailed topographic survey was done to obtain a high-resolution digital elevation model (2.5 m) of the study field and Cs-137 derived soil redistribution rates were used to calibrate the model. In the study field, soil erosion predominated over soil deposition. Mean values of Cs-137 derived soil erosion and deposition rates were 19.7 Mg ha(-1) yr(-1) and 12.6 Mg ha(-1) yr(-1), respectively. Water erosion was the predominant process of soil redistribution whereas tillage erosion was not significant. The rates obtained with WATEM/SEDEM model were lower; mean erosion was 3.9 Mg ha(-1) yr(-1) and mean deposition rates that occurred in 35% of the grid cells was of 5.8 Mg ha(-1) yr(-1). The use of spatially-distributed models is required to better quantify soil redistribution processes and to evaluate superficial soil distribution. However, point-estimates of soil redistribution such as those provided by Cs-137 are required to allow calibration of the models. The knowledge about the spatial distribution of erosion processes is a useful tool for the application of effective soil erosion control and prevention strategies on water and tillage erosion on agroecosystems. (C) 2015 Elsevier B.V. All rights reserved.