First assessment of lakes' water quality in Aras River catchment (Turkey); Application of phytoplankton metrics and multivariate approach

This study is the first attempt to determine responses of phytoplankton assemblages to stressors using multi-variate approaches and to evaluate the limno-ecological status of Akta , Cldr, Aygr, Deniz and Balk lakes in the Aras River system (Turkey) using phytoplankton metrics according to the requirements of Water Framework Directive. Samples were collected in August and October of 2014, and June of 2015 by using the standard protocols. The first two axes of canonical correspondence analysis (CCA) elucidated strong correlations (lambda 1 = 0.937, 99.7% and lambda 2 = 0.763, 98.5%) between phytoplankton species and stressors with a 27.2% of the cumulative variance of species data. The Monte Carlo permutation test with the forward selection exhibited the significant effects of dissolved oxygen, orthophosphate (P-PO4), total phosphorus (TP), biological oxygen de-mand (BOD5), water temperature, nitrite (N-NO2), and altitude on the phytoplankton distribution among lakes. Lake Akta was closely related to N-NO2, TP, P-PO4, and BOD5 and characterized by species Messastrum gracile, Oocystis borgei, Treubaria triappendiculata, Snowella lacustris, Tetraedron minimum, and Lemmermannia komarekii. They preferred N-NO2 higher than 90th percentile (0.026 mg/L) and TP higher than the 75th percentile (0.270 mg/L). Phytoplankton trophic index (PTI) scores varied from 2.06 in Lake Aygr to 2.36 in Lake Akta , while a range between 0.89 in Lake Akta and 1.81 in Lake Aygr was calculated according to Mediterranean phytoplankton index (Med-PTI). The correlations of PTI and Med-PTI (R-2 = 0.94 and 0.90, respectively) with logTP gradient indicated congruent results. A high ecological status was found in Lake Cldr, when Aygr, Deniz, and Balk lakes had good environmental conditions. Lake Akta showed a moderate ecological condition. The present study confirmed that phytoplankton assemblages closely integrated with the limno-ecological status of lakes in the Aras catchment, which could be assessed by using the PTI and Med-PTI.