Estimating soil redistribution patterns with 137Cs measurements in a Mediterranean mountain catchment affected by land abandonment

Abstract

In Mediterranean mountainous environments, the removal of natural vegetation for developing agriculture increased the surface areas prone to erosion in the past centuries. In Southern Pre-Pyrenees, the process was inverted during the middle of the 20th century. This work aims to assess how land use changes after widespread land abandonment affect soil redistribution. For this purpose, 137Cs was used in a 23 km2 catchment that was mostly cultivated at the beginning of the past century. After land abandonment, 16.5% of croplands persisted but afforestation and natural revegetation occupy 83.5% of the catchment area. 137Cs massic activity and related soil properties—stoniness, grain size, and organic matter contents—were analysed in 98 bulk core samples. Physiographic characteristics—slope, altitude, and solar radiation—at the sampling points were determined by using Geographic Information Systems. Soil erosion and deposition rates were derived from 137Cs measurements after applying conversion models and were spatially interpolated to estimate the amount of net soil loss. In cropland soils, mean erosion (62.6 Mg ha−1 yr−1) and deposition rates (55.2 Mg ha−1 yr−1) were significantly higher than in the other land uses. The lowest mean erosion rates (2.4 Mg ha−1 yr−1) were found in natural forests and the lowest mean deposition (2.6 Mg ha−1 yr−1) in pine afforestation evidencing the soil stabilization achieved in the last decades due to revegetation. A sediment budget with the interpolated rates, result in a specific sediment yield of 4.15 Mg ha−1 yr−1. These results outline the impact of land use changes on soil redistribution in fragile mountain agroecosystems.