Loss of phytoplankton functional and taxonomic diversity induced by river regulation in a large tropical river.

Human activities have disrupted the functioning of river ecosystems around the world. In the Amazon basin, hydropower expansion has affected diversity patterns, but no study has investigated how phytoplankton assemblages respond to impoundments. This study investigated the hypothesis that phytoplankton diversity is highly sensitive to river damming in large tropical rivers, declining in impoundment areas. We examined patterns of taxonomic diversity (i.e., richness, biovolume, and composition), functional diversity (Reynolds Functional Groups, RFGs), and functional redundancy (i.e., number of taxa in each RFG) along the Tocantins River, before and after the construction of Estreito Hydropower Dam. We monitored five sites along the river (ca. 260 km) between December 2009 and May 2013. The dam changed environmental conditions related to flow, nutrient supply, and depth. We recorded 140 taxa and 26 RFGs in the area. Taxa richness, biovolume, and the number of RFGs declined significantly after river regulation. Composition and abundance ranks changed over periods, and the codons C, Y, TC, W1, and LO were eliminated; functional redundancy declined significantly. These results show that phytoplankton diversity is sensitive to river regulation in large tropical rivers, where changes in hydrology and environmental filters lead to significant losses in taxonomic and functional diversity. [ABSTRACT FROM AUTHOR]