Ecologic implications at a large junction of highly unequal discharges and sediment loads

This paper examines changes in the benthic fauna along the Paraguay River (Paraguay- Argentina), up- and downstream its confluence with the Bermejo River (Argentina), which supplies large inputs of suspended fine sediment to the Paraguay River, mostly in suspension. Biotic (benthic invertebrates) and abiotic data at several cross-sections along the Paraguay River and in the Bermejo River clearly show how the significant loading of sediment changes drastically the abundance and richness of the benthic assemblage of the Paraguay River with effects still discernible up to 70 km downstream the junction. While there is no evidence of increasing sediment loads of the Bermejo River due to anthropogenic impacts, this case illustrates how human influences on sediment yield could be conveyed through confluences, thereby affecting the ecology of large river ecosystems.