Brazilian Pantanal: A Large Pristine Tropical Wetland

Abstract

The Pantanal is a Quaternary sedimentary basin located in the central-west region of Brazil. Its origin has been linked to stresses transmitted from the western margin of the South American continent into the interior of the craton. Therefore, the Pantanal is part of the Andean foreland system. It presents alluvial plain morphology with altitudes between 80 and 200 m surrounded by desiccated plateaus. Northeast-southwest-aligned faults, many associated with the Transbrasiliano Lineament, control part of the drainage network within the Pantanal Basin. The Paraguay River meanders through an extensive fluvial plain, bordering Precambrian terrains at the western edge of the basin. The Paraguay River is the main river of a depositional system characterized by fluvial megafans, among which the Taquari River megafan stands out. Since the Late Pleistocene, the Pantanal landscape has been changing in response to a climate shift from colder and drier to wetter and warmer conditions. These climate changes are recorded in the Pantanal landscape, which is marked by relict depositional landforms of varying ages formed in environmental and climatic conditions differing from the present. The thousands of Nhecolândia lakes located in the southern sector of the Taquari megafan are examples of relict landforms. These lakes are mostly freshwater lakes connected through rainwater runoff, forming wide and shallow channels (locally called “vazantes”) that drain the fluvial plain during and after the wet season. In contrast, some saline lakes (locally called “salinas”) remain isolated from the surface drainage and are relict landforms of a degrading landscape. The Pantanal is a large tropical wetland exhibiting mostly native vegetation, where wildlife is preserved in its natural habitats. The rivers building the fluvial megafans are prone to frequent avulsions, shifting their channels according to sediment infilling dynamics in the fluvial plain. These shifts in river courses result in considerable changes in the hydrography and geography of the flood plain.