Soil erosion evaluation in a small basin through the use of 137Cs technique

Soil erosion significantly affects the most productive lands in Argentina, particularly the region called "Pampa Ondulada". Quantification of the actual rates and patterns of soil loss is necessary for designing efficient degradation control strategies. The aim of this investigation was to gather using the Cs-137 technique a reliable set of data of erosion and sedimentation rates, in order to describe the long-term erosive landscape dynamic in a 300 ha basin representative for the "Pampa Ondulada" region of Argentina. The general topography of the basin is undulated with slopes gradients between 0 and 2.5% and slope lengths up to 800 m long. The main land use consisted in annual cropping under conventional tillage. For the soil erosion study in the basin the Cs-137 technique was used, which is based on the comparison between the Cs-137 inventories surveyed with a local reference Cs-137 profile. The sampling strategy was based on a multiple transect approach. The estimated mean soil erosion rates obtained applying Mass Balance Model 2 for the studied hillslopes ranged between -11.5 and -36 t ha(-1) per year and fitted the low and moderate erosion classes according to FAO. These values ranged beyond the admitted tolerance. Sedimentation was observed at the lower landscape positions probably related to changes from convex to concave slopes. The application of the Cs-137 technique in the studied basin proved to be a useful and sensible tool for assessing erosion/deposition rates. In areas with low topographic gradients like the Pampa Ondulada region, the slope length appears to be an important property for predicting spatial patterns of erosion rates. (C) 2002 Elsevier Science B.V. All rights reserved.