The first eco-assessment of thirteen lakes in the Lake Van Basin of Türkiye with phytoplankton metrics as indicators of environmental conditions

Abstract

Lakes are increasingly vulnerable to anthropogenic pressures such as pollution, eutrophication, and climate change, leading to biodiversity loss and ecosystem degradation. This study employed phytoplankton-based metrics across two hydrological periods to evaluate species-environment interactions and assess the ecological status of thirteen lakes in the Lake Van Basin. Canonical correspondence analysis (CCA) showed a strong correlation (96.7 %) between phytoplankton assemblages and environmental stressors. The most influential factors affecting phytoplankton distribution were conductivity, total organic carbon, total suspended solids, total phosphorus, total nitrogen, and nitrate. The CCA clearly distinguished the soda lakes, Lakes Erçek and Sodalı, which were characterized by high conductivity, alkaline pH, and high total organic carbon, and hosted assemblages dominated by taxa tolerant to organic pollution and salinity. In contrast, Lake Hıdırmenteş supported phytoplankton communities adapted to elevated nutrient and turbidity levels, while the Ahlat Marshes were associated with species indicative of nitrogen enrichment. The MPTI−modified phytoplankton trophic index proved to be an effective tool for ecological assessment, showing a strong correlation with total phosphorus (r = 0.925, p < 0.01). The MPTI indicated that Lakes Nemrut, Aygır, and Nazik had a high ecological status, whereas Lakes Erçek, Hıdırmenteş, and Adırum showed a poor status and Lakes Turna and Hasantimur had a moderate one. This first eco-assessment of the region underscores the value of phytoplankton as sensitive indicators of environmental stress and supports the application of the MPTI for ecological status classification in saline and freshwater lakes of the Lake Van Basin.