Benthic invertebrates structure in wetlands of a tributary of the middle Parana River (Argentina) affected by hydrologic and anthropogenic disturbances

The present study was aimed at analyzing chromium concentrations in water column and bottom sediments in the main channel of Northern Salado River (tributary of Middle Parana River) and its floodplain. The main changes caused by human activities and hydrological disturbances on benthic in vertebrate structure were also analyzed. Sediment concentrations of the reference area varied between 44.2 and 97.1 mu g Cr g(-1) (dw), and in the impacted zone, between 85.5 and 209 mu g Cr g(-1) (dw) reaching the highest values in the wetland floodplain. Alfa, beta and gamma diversities in the reference section have been 33, 9 and 66 species, and in the disturbed section, they have been 37, 8.33 and 74 species, respectively. The species dominant in the disturbed habitats were characterized by a small body size and short life cycles, as the species of oligochaetes Naidinae. The extreme flooding produced a rejuvenation of the area with the consequent physical re-structuration produced by flooding, showing a marked decrease in chromium levels in sediments and in organic matter content, which allowed the colonization of insects (Ephemeroptera and Trichoptera).