Land degradation due to soil erosion in the Mediterranean olive groves: A comparison of 137Cs, 239+240Pu radionuclides and 3D reconstruction of surface levels

Abstract

Olive tree plantations, an ancient and traditional crop in the Mediterranean region, have become erosion-prone due to their soil management and location. Many olive groves are often planted on slopes, where soil management often keeps the soil bare by conventional tillage and/or herbicide use. Further, the natural conditions of the region as long drought periods followed by intensive rainfall episodes, intensify the susceptibility to erosion. As a result of these factors, soil erosion has become a major threat to the sustainability of olive cultivation in southern Spain. On-site soil erosion measurements through conventional methods usually do not exceed one decade and present several discrepancies among them and with modelling outcomes. Here, we aim to use fallout radionuclide (FRN) inventories (137Cs, 239+240Pu) together with 3D reconstruction of surface levels to estimate soil erosion rates at appropriate temporal and spatial scales for the last 55-60 years and/or from the beginning of tree plantation. Twelve soil cores up to 40 cm depth were taken across olive groves and in identified reference sites, and the model MODERN (Modelling Deposition and Erosion rates with RadioNuclides) (Arata et al., 2016) was used to estimate soil erosion rates from 1960. For the geomorphological reconstruction, manual measurements were taken to recreate the historical soil surface using the germination point in the olive trees as a reference point to the current soil surface. Both methods allowed us to estimate and understand past erosion processes and possible long-term trends. The radiochemical analysis content of 137Cs, 239+240Pu inventories and its correlation with a geomorphological reconstruction on selected olive tree fields under different soil management in southern Spain will be presented.   Arata, L., Meusburger, K., Frenkel, E., A’Campo-Neuen, A., Iurian, A.-R., Ketterer, M. E., Mabit, L., & Alewell, C. (2016). Modelling Deposition and Erosion rates with RadioNuclides (MODERN) – Part 1: A new conversion model to derive soil redistribution rates from inventories of fallout radionuclides. Journal of Environmental Radioactivity, 162–163, 45–55. https://doi.org/10.1016/j.jenvrad.2016.05.008