Benthic diatoms in relation to environmental factors in an allochthonous river from Patagonia, Argentina

Abstract

Natural and human pressures increasingly threaten the biodiversity and water resources of the dryland rivers. Fluvial environments of Patagonia are known to be a refuge of diatom diversity, but their management value is overlooked. This study aims to explore the distribution patterns of diatoms in surface sediments from the Chubut River, and to evaluate their relationship with environmental variables using gradient analysis. A total of 243 diatom taxa were identified in 16 sampling sites collected from the littoral zone. The physical and chemical variables explained independent amount of variance in the diatom data, whereas the sediment texture had a much less influence. Conductivity, major ions and pH were the major environmental drivers explaining the variation in diatom composition. As the highlighted variables increased, so did the relative abundances of brackish and marine taxa such as Amphora copulatoides, Sarcophagodes alfred-wegeneri, Nitzschia fonticola and Tryblionella apiculata. Moderate and high pollution-tolerant taxa suggest an increase in the nutrients load downstream of the river, despite the contribution of nitrates to diatom distribution was more unclear. Brackish-marine taxa occurring at the freshwater sites reflect a weak tidal influence in the estuary compared with other coastal system of Patagonia. This study provides valuable information to test the hypothesis concerning the ecological status of the aquatic resources and the potential effects of the climatic and hydrological changes in the area.