Determination of ecological status and ecological preferences of phytoplankton using multivariate approach in a Mediterranean reservoir

The European Union Water Framework Directive includes phytoplankton as one of the mandatory five biological indicators to be used to assess the ecological status of surface waters. The objective of the study was determination of ecological status and ecological preferences of phytoplankton from April 2012 to June 2013, using multivariate approach in Alleben Reservoir in the southeast Turkey. The reservoir showed a warm monomictic stratification pattern (stratification in April-October 2012 vs. mixing in November 2012-March 2013). The reservoir was meso-eutrophic according to phosphorus, chlorophyll a, and transparence values. Phytoplankton biovolume reached remarkable peaks in autumn and spring. Phytoplankton species belong to functional groups of A, D, E, J, L-O, L-M, MP, P, and Y as descriptor. Phytoplankton trophic index (PTI) and assemblage index (Q) indicated the overall medium ecological status of Alleben Reservoir. PTI and Q indices may be appropriate phytoplankton metrics to assess the ecological status of the reservoir. Changes in environmental gradients significantly influenced the ecological preferences of species and phytoplankton abundance in the reservoir. Canonical correspondence analysis (CCA) confirmed that phytoplankton species were sensitive to environmental variability, with the first two axes of CCA able to explain 92.8% of the total variation and 37.1% of the cumulative percentage variance in the phytoplankton assemblage structure. Most effective explanatory factors (e.g., salinity, conductivity, pH, and temperature) played significant role (P = 0.002) in the seasonality of species.