Eco-assessment of West Mediterranean basin's rivers (Turkey) using diatom metrics and multivariate approaches

Bio-evaluating of surface waters is not a new approach but is becoming more important since the application of the European Water Framework Directive (WFD). The present study was designed to evaluate the limno-ecological conditions of rivers in the West Mediterranean basin of Turkey using diatom metrics and multivariate approaches according to the WFD requirements. Canonical correspondence analysis (CCA) was used to assess the relationships of diatom species and environmental variables from 17 stations of 12 rivers sampled in two seasons. The CCA indicated that nitrite, chloride, electrical conductivity (EC), sulfate, temperature, and total phosphorus (TP) are the most explanatory factors on the distribution of the diatom species. Karasu River had the most deteriorated ecosystem, distinctly revealed by the CCA. Nutrient enrichment and high EC, biological oxygen demand (BOD₅), and temperature values were noticed in this ecosystem. Karasu River was also characterized by pollution tolerant diatom species (e.g., Nitzschia inconspicua, Nitzschia pusilla, Halamphora normanii, and Rhoicosphenia abbreviata). Trophic index Turkey (TIT), eutrophication and/or pollution index-diatom (EPI-D), and trophic index (TI) showed poor ecological conditions in Karasu and Hamzabey rivers when a moderate environment quality in Dalaman River (at R6 station) and a good ecological state in Kocadere River. A high ecological status was found in Dalaman (at R5 station) concerning the results of TIT and TI, while a good condition was recorded based on EPI-D. This ecosystem was also associated with pollution-sensitive diatom taxa (Achnanthidium minutissimum, Cymbella excisa, Meridion circulare, and Gomphonema olivaceum). Results of CCA were corroborated with the bio-assessment of sampling stations based on diatom metrics. TIT, TI, and EPI-D had different indices' scores, but they showed significantly positive correlations with logTP. Spearman correlation coefficient value of TIT strengthens the suitability of it for the bio-assessment of the rivers in the West Mediterranean basin of Turkey.