Hydrochemical variability at the Upper Paraguay Basin and Pantanal wetland

Abstract

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 (EndMembers Mixing Analysis) procedure shows that the chemistry of the rivers can be viewed as a mixture of 3 endmembers, 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 PCAbased 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 Ksilicates) explained more than 77 % of the total variability in the chemistry of the regional surface water sampling.

Chemical diversity and spatial variability in myriad lakes in Nhecolândia in the Pantanal wetlands of Brazil

“…4b) could be attributed either to local soil transformations involving redox processes or to fertilization pollutants from an extensive agricultural area located upstream on the plateau, which consists mainly of a combination of both KCl and (NH 4 ) 2 SO 4 enriching agents. Overall, the waters in the region result from simple concentration and dilution of one original source, the chemical composition of which is close to that of the Taquari River (Rezende-Filho et al 2012). The sum of the contribution to the total variance for both factorial axes 1 and 2 (Fig.…”

“…The second set (TR) consists of 74 sites collected in 2004 along a north-south transect from the Brazilian Agricultural Research Corporation's (EM-BRAPA) experimental farm (Nhumirím farm) to the margins of the Negro River. This second sample set was described in Rezende-Filho et al (2012) and was chosen so as to intersect the regional drainage that is oriented eastnortheast-west-southwest, therefore maximizing the variability. The first two data sets are georeferenced.…”

“…Moreover, the chemical composition of surface waters is the result of evaporation of the Taquari River water at different concentration stages (Rezende-Filho et al 2012). Therefore, the presence of salinity could be explained by differential hydrological functioning of each type of lake.…”

“…Recent studies have reported on fluvial geomorphology, seasonal inundation, and biogeochemical cycling (Bastviken et al 2010;Zani et al 2012;Evans and Costa 2013), but few papers have focused on the functioning of its lakes (McGlue et al 2011(McGlue et al , 2012. The Pantanal wetland lies in the heart of South America and consists of a patchwork of subregions with highly contrasted hydrological, chemical, or pedological features (Rezende-Filho et al 2012). Plans for canalization of the Paraguay River, known as the Paraguay-Parana Hidrovia project, potentially place at risk the natural flood regime of broad areas within the Pantanal, but future anthropogenic effects may vary according to the characteristics of each subregion.…”

Genesis and Classification of Sodic Soils in the Northern Pantanal

“…Rezende Filho et al (2012) analyzed the chemical composition of the main rivers flowing into the Pantanal and observed that the São Lourenço river has alkaline-sodic waters that, when concentrated, favor control of Ca 2+ by formation of carbonates, resulting in pH above 8.0 (Al-Droubi et al, 1980). The geomorphology of the flood plain of the São Lourenço River has several depositional lobes at different stages of dissection.…”