The lakes of the Pantanal: inventory, distribution, geochemistry, and surrounding landscape

The Brazilian Pantanal is an ecosystem of high biodiversity. This biodiversity is largely supported by the dynamic hydrology and landscape of the region. As part of the mosaic of this unique landscape, there are a variety of geochemically diverse lakes in the lower Nhecolândia (LN) sub-region. The goal of this study was to provide an inventory, spatial distribution, and geochemical analysis of the lakes, and the characteristics of the associated surrounding landscape of the LN region in the Pantanal, and to use that information to further add to the hypotheses on lake formation. To accomplish this, we made use of: (i) the spatial distribution of lakes and surrounding landscape units from a classification product generated from a combination of fine pixel resolution L-band ALOS/PALSAR, C-band Radarsat-2, and Envisat/ASAR; and (ii) in situ measured lake water geochemical properties.With an accuracy of 98 %, we found that the LN sub-region has 637 salinas and 8,214 baías. The greatest degrees of salinas clustering are located in the southeast portion of the study area, and are surrounded by forested savanna, which are in higher grounds less prone to flooding. Baías, however, are more broadly distributed in the region, and the highest occurrence is associated with the open mixed cover, comprised mostly of grasslands, which are in flood-prone areas. Geochemically, salinas present a pH > 9.0 and total dissolved solids (TDS) generally >1,000 mg/L, while baías have a circum-neutral pH not much higher than 7.0, and TDS < 1,000 mg/L. Another group of lakes, locally called salitradas, have pH > 9.0, comparable to the salinas, but relatively lower TDS and conductivity, and significant lower chloride. The combination of the regional scale spatial data and associated geochemistry of lakes suggests that the geomorphological characteristics of the region, and consequent undulating terrains, create groundwater divides and groundwater-sheds that can develop local and regional flow systems and lead to lakes with different geochemistry. The mechanisms responsible for the formation of the diversity of lakes in the region is likely due to combination of isolation from ground water/surface water recharge, evaporation, episodic flushing, and biogeochemical processes in the lake’s watersheds.