Relações entre o regime hidrológico e os ecossistemas aquáticos da planície aluvial do rio Araguaia

The Araguaia river is the most important fluvial system draining the Cerrado biome of Brazil. Results are presented here on the hydro-geomorphologic behavior of this fluvial system and its effect on the floodplain ecosystems. Discharge from nine gauge stations in the upper, middle and lower course of the Araguaia River, from 1970 to 2004, were analyzed. The hydrological regime depends strongly on the tropical wet-dry climate, with floods from January to May and low water between June and September. In the upper and lower courses, there is a high variation between maximum and minimum peaks because the underdevelopment of the floodplain, while in the medium course the flow peaks are smoothed by the presence of a well-developed river floodplain. In this area, the river can lose up to 30% in water discharge, which is stored in the floodplain. Three types of flood categories were defined, and two mechanisms of flow storage and transfer were identified, explaining the discharge loss in the middle course. Three main mechanisms produce the water loss mid-course: the sponge effect of the alluvial plain, the existence of a well-developed mosaic of lakes, and an arboreal-dominated vegetation stratum of alluvial forest.