Hydrology-driven seasonal changes in the phytoplankton of a subtropical river (Riacho Formosa, Argentina).

Abstract

The Riacho Formosa is one of many autochtonous watercourses running along the subtropical region of the Wet Chaco Plains and draining into Paraguay River. Their typical hydrological cycle is characterized by a late winter low phase and a high phase throughout the warm season. As part of a baseline characterization, the composition and structure of the phytoplankton were studied in relation to river depth, water temperature, pH, conductivity and transparency through 4 seasonal samplings between June 2015 and March 2016. A rich phytoplankton community (338 taxa) was revealed in this study. A few species of Cryptophyceae and Euglenophyceae dominated the community, especially during low waters. A cluster analysis showed that community compositions were more dissimilar over time than along the watercourse, and were spatially more homogeneous during high waters. A canonical correspondence analysis showed that environmental features significantly explained 42.6% of the total variance of species data (p= 0.004). We conclude that phytoplankton responds to hydrological changes through a high species turnover, with dominance peaks of euryhaline, shadow adapted and organic matter exploiting taxa during low waters.