Alkaline lake dynamics in the nhecolândia landscape

Abstract

Alkaline lakes are diversified ecosystems of the Nhecolândia landscape in the southern Taquari Megafan, Pantanal. By 1985 they covered an approximate area of 1,060 km2 distributed in nearly 12,761 shallow water bodies. Historical Landsat-5 image analysis from 1985 to 1998 indicates a reduction of 24% in the area and 28% in the number of these shallow lakes. The alkaline lakes in the region can be generally arranged in three major ecological typologies: macrophyte lakes (autotrophic above waterline, lower electron conductivity (EC), and pH), bacterial lakes (heterotrophic, moderate EC, and pH), and saline lakes (autotrophic below waterline, elevated EC, and pH). During 1985–1998, the relative area of macrophyte lakes and bacterial lakes decreased 22 and 40%, respectively, while saline lakes increased 53%. Alkaline lakes may interchange their ecological typologies as a function of short- and long-term water rainfall, surface water flows, and interplay with the aquifer. The decline of lake area and number, and the particular increase in saline lakes, can be associated to highland deforestation and its impact on the regional rainfall distribution. Ancillary data of water chemistry and greenhouse gases allowed sketching a general biogeochemical model of macrophyte and saline typologies and deriving a gross estimation of carbon exchanges with the atmosphere from these alkaline lakes in the Nhecolândia landscape.