Assessing soil erosion in a semiarid ecosystem in Central Argentina using 137Cs and 7Be measurements

Abstract

Argentina is a Latin American country which encounters soildegradation problems. The most productive regions haveimplemented conservative land practices (no-till). However,agricultural frontier has been displaced to marginal lands witharid and semiarid climates, with the consequent disappearance inmany areas of native forest and land degradation. In this work,the fallout of gamma-emitting radionuclides, 137Cs and 7Be, wasjointly used to assess changes in soil erosion in a recentlyconverted semiarid ecosystem into agricultural land. 137Cs wasutilized to estimate the erosion over the past 60 years, whereas7Be was employed to estimate the erosion after the conversion ofthe area to cultivated land and soil tillage. For 137Cs theProportional Model (PM), the Mass Balance Model II (MBMII) andthe MODERN model were used, for 7Be the Profile DistributionModel (PDM) and the MODERN model were used. 137Cs indicatesmean erosional rates of 8.2, 10.5 and 6.5 Mg ha−1 a−1, usingMBMII, PM and MODERN, respectively, and that a soil layerbetween 0.5 and 0.8 mm was annually lost by erosion. Byapplying a 7Be tracer, we measured erosion rates of 2.4 and3.3 Mg ha−1 (with PDM and Modern, respectively), indicating theloss of the upper 0.2 mm of soil. This erosion can be attributed toa few heavy rainfalls that occurred within the past 90 days. Theresults suggest that current land management practices have ledto an increase in soil erosion. This could be attributed to the factthat the soil remains bare after crop harvest, which maycompromise its conservation and future productivity.