Impacts of lithological and anthropogenic factors affecting water chemistry in the Upper Paraguay River Basin

International audienceLocated in the Upper Paraguay River Basin (UPRB), the Pantanal is considered the world's largest wetland, being rather pristine although increasingly threatened by development programs. The main objective of this paper is to provide a baseline of water chemistry for this region, which is largely unknown due to poor accessibility. We used two datasets (70 and 122 water samples) collected in the Pantanal floodplain and surrounding uplands during the wet season occurring from November to March. From the major ions mineral chemistry, dissolved silica, pH, electrical conductivity, and the ionic forms of nitrogen, principal components analysis (PCA) treatments were used to identify and rank the main factors of variability and decipher the associated processes affecting the water chemistry. The results revealed that the water mineral concentration was a major factor of variability and it must be attributed first to lithology and second to agricultural inputs from extensive crop cultivation areas that mainly affects sulfate concentration on the eastern edge of the Pantanal. These processes influence the floodplain, where (1) the mixing of waters remains the main process, (2) the weight of the biological and redox processes increased, and (3) the chemical signature of the extensive cropping is transferred along the São Lourenço basin down to its confluence with the Cuiaba River. Optimized parameters based on projections in the main factorial score plots were used for the mapping of lithological and agricultural impacts on water chemistry