Hydrochemical variability at the Upper Paraguay Basin and Pantanal wetland
- 1Universidade Federal do Mato-Grosso do Sul, Departamento de Geografia, Campus de Nova Andradina, Rod. MS 134, Km 3, Campus Universitário s/n, C.P. 128 79750-000, Nova Andradina-MS, Brazil
- 2Universidade de São Paulo, Laboratório de Pedologia, Departamento de Geografia, C.P. 8105, Cep 05508-900 São Paulo, Brazil
- 3Universidade de São Paulo, Centro de Energia Nuclear na Agricultura, Laboratório de Análise Ambiental e Geoprocessamento, Av. Centenário, 303, C.P. 96, Cep 13416-000 Piracicaba-SP, Brazil
- 4Université d'Avignon et des Pays du Vaucluse, Laboratoire d'Hydrogéologie, 74 rue Louis Pasteur, 84029 Avignon Cedex 01, France
- 5Université Paul Sabatier, Géosciences Environnement Toulouse, Institut de Recherche pour le Développement, Observatoire Midi-Pyrénées, 14 Av. E. Belin, 31400 Toulouse, France
Abstract. Compartmentalization is a prerequisite to understand large wetlands that receive water from several sources. However, it faces the heterogeneity in space and time, resulting from physical, chemical and biological processes that are specific to wetlands. The Pantanal is a vast seasonally flooded continental wetland located in the centre of South America. The chemical composition of the waters that supply the Pantanal (70 rivers) has been studied in order to establish a compartmentalization of the wetland based on soil-water interactions. A PCA-based EMMA (End-Members Mixing Analysis) procedure shows that the chemistry of the rivers can be viewed as a mixture of 3 end-members, influenced by lithology and land use, and delimiting large regions. Although the chemical composition of the end-members changed between dry and wet seasons, their spatial distribution was maintained. The results were extended to the floodplain by simple tributary mixing calculation according to the hydrographical network and to the areas of influence for each river when in overflow conditions. The resulting map highlights areas of high geochemical contrast on either side of the river Cuiaba in the north, and of the rivers Aquidauana and Abobral in the south. The PCA-based treatment on a sampling conducted in the Nhecolândia, a large sub region of the Pantanal, allowed the identification and ordering of the processes that control the geochemical variability of the surface waters. Despite an enormous variability in electrical conductivity and pH, all data collected were in agreement with an evaporation process of the Taquari River water, which supplies the region. Evaporation and associated saline precipitations (Mg-calcite, Mg-silicates K-silicates) explained more than 77% of the total variability in the chemistry of the regional surface water sampling.