The Green Revolution of the 1960s led to a significant increase in cultivated areas at the expense of natural ecosystems, particularly in South America. This cultivation of soils led to an increase in erosion rates and the siltation of water bodies downstream. However, very limited data is available to quantify these phenomena and there is a debate raging about their extent within the scientific community. To make up for this lack of data, the measurement of cesium-137 (137Cs) inventories in soils enables a posteriori reconstruction of erosion rates. This radioisotope, which fell back onto the soil following atmospheric nuclear tests in the 1960s, binds strongly to clay particles. A comparison of 137Cs stocks in disturbed soils, on the one hand, and soils preserved since the 1960s, on the other hand, thus makes it possible to quantify erosion rates over the last few decades.
A study conducted by the LSCE, in collaboration with its partners at INRAE and several universities in Brazil and Uruguay, synthesised the information available in the literature. The results confirm that the spatial distribution of 137Cs fallout is highly dependent on latitude, with a maximum between 30 and 50° South. The levels of fallout estimated in this way are higher than those revealed by previous estimates (UNSCEAR reports). Statistical analysis was used to create a reference map of 137Cs deposition in soils on the continent. The potential application of the 137Cs inventory technique is examined in the light of this comprehensive literature review. The areas to be sampled as a priority in the future to improve this first map were also highlighted (Andean foothills, Colombia, Peru...). This reference map could also have many other applications in Earth sciences (pedology, climatology...).
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Mapping the spatial distribution of global 137Cs fallout in soils of South America as a baseline for Earth Science studies – Earth Science Reviews
Pierre-Alexis Chaboche, Nicolas P.A. Saby, J. Patrick Laceby, Jean P.G. Minella, Tales Tiecher, Rafael Ramona, Marcos Tassano, Pablo Cabral, Mirel Cabrera, Yuri Jacques Agra Bezerra da Silva, Irène Lefevre, Olivier Evrard