Phytoplankton response to water quality seasonality in a Brazilian neotropical river.

Tropical wet-dry climate seasonality is widely recognized as an important condition to phytoplankton communities' structure in freshwater ecosystems; however, there are few studies in that field in northeast Brazilian rivers. This study aimed to evaluate the influence of water quality seasonal variability over the phytoplankton dynamics and identify seasonality in eutrophication phenomena in a poorly studied neotropical river. Water quality variables and phytoplankton were examined within the Jequitinhonha River lower course, Bahia (Brazil) from 2010 to 2012. A 3-year time series was analyzed for both rainy and dry seasons. Descriptive, inferential, and multivariate analyses (CCA) were performed. Results indicated that chemical oxygen demand, dissolved aluminum, and turbidity were the main factors which influenced phytoplankton community structure and composition. Dry season was favorable for diatoms and Chlorophyceae (chlorophylls) while rainy season was favorable for cyanobacteria. Still, it was revealed that, in dry season, lower values for turbidity, chemical oxygen demand, dissolved aluminum, and dissolved iron were related with an eutrophication phenomenon.