Threats for biodiversity in the floodplain of the Upper Paraná River: effects of hydrological regulation by dams

Abstract

The Paraná River is the main tributary of the La Plata River and runs through 4,695 km. Its third upper part, the Upper Paraná River, is almost completely inside the Brazilian territory. In this area, there are more than 130 major reservoirs that inundated most of the river-floodplain system. The stretch left, about 230 km, is the area where a Long Term Ecological Research (LTER; Site 6) is developed. The floodplain presents itself as a mosaic of habitats (river channels, secondary channels and lagoons) with peculiar characteristics, depending on local and/or regional processes. Surveys conducted in the area since 1986 registered about 2,920 species (745 of terrestrial plants; 60 of macrophytes; 543 of phytoplankton; 385 of zooplankton; 188 of benthos; 176 of fish and 417 of vertebrates). Besides the intense regulation by dams, the flood pulse is still the main function force working on the floodplain. Then, the flood pulse plays important role determining the dynamic of abiotic factors and organisms that live or use the plain for at least one stage of the life cycle. Main impacts in the area are natural, such as climatic (effects of "El Niño") and anthropogenic, such as damming (the most conspicuous), cattle raising and removal of riparian vegetation. It is concluded that the maintenance of the biodiversity of the area will depend on the integrity of the land-inland water ecotone, represented by the floodplain, especially for large migratory fish species. Then, it is suggested a creation of a permanent floodplain reserve, according to biosphere reserve from MAB/UNESCO.