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

Abstract

This study is the first attempt to determine responses of phytoplankton assemblages to stressors using multivariate approaches and to evaluate the limno-ecological status of Aktaş, Çıldır, Aygır, Deniz and Balık 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 (λ1 = 0.937, 99.7% and λ2 = 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 demand (BOD5), water temperature, nitrite (N-NO2), and altitude on the phytoplankton distribution among lakes. Lake Aktaş was closely related to N-NO2, TP, P-PO4, and BOD5 and characterized by species Messastrum gracile, Oocystis borgei, Treubaria triappendiculata, Snowella lacustris, Tetraëdron 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 Aygır to 2.36 in Lake Aktaş, while a range between 0.89 in Lake Aktaş and 1.81 in Lake Aygır was calculated according to Mediterranean phytoplankton index (Med-PTI). The correlations of PTI and Med-PTI (R2 = 0.94 and 0.90, respectively) with logTP gradient indicated congruent results. A high ecological status was found in Lake Çıldır, when Aygır, Deniz, and Balık lakes had good environmental conditions. Lake Aktaş 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.