An Ecoregion-Based Assessment of Lakes in Türkiye With Phytoplankton Metrics and Multimetric Approaches

This study investigates the environmental characteristics, phytoplankton community dynamics, and ecological status (ES) of lakes in different ecoregions. Significant variations were observed in environmental variables across the lakes. Lake Kuğu, a brackish ecosystem, recorded the highest electrical conductivity (EC = 9810 μS/cm), while Lake Uzungöl showed the lowest EC values (47 μS/cm). Lake Karagöl exhibited the highest levels of total phosphorus (TP = 349 μg/L), total nitrogen (TN = 15.12 mg/L) and total organic carbon (TOC = 76.7 mg/L), reflecting eutrophic conditions. Conversely, Lake Uzungöl displayed the lowest TP and TN values and oligotrophic characteristics. Phytoplankton biovolume ranged from 0.40 mm³/L in Lake Borçka Karagöl to 15.47 mm³/L in Lake Karagöl. Canonical correspondence analysis (CCA) revealed strong associations (98.9%) between specific phytoplankton taxa and environmental gradients, with Lake Kuğu being characterized by pollution-tolerant taxa favouring high conductivity; Lake Karagöl being influenced by elevated TP, TN and TOC levels; and Lake Sera having high NO₃⁻. Microcystis flos-aquae, Lepocinclis oxyuris, Eunotia bilunaris, Nitzschia tubicola and Hantzschia amphioxys were found in Lake Karagöl and are relatively high in nutrient. Trophic state assessments using indices based on TP, TN, Secchi depth and chlorophyll-a identified Lake Kuğu and Lake Karagöl as hypertrophic, Lake Sera as eutrophic, Lake Borçka Karagöl as mesotrophic and Lake Uzungöl as oligotrophic. ES evaluated using multiple phytoplankton metrics (Modified Phytoplankton Trophic Index [MPTI], biological condition gradient [BCG], Aquatic Biotic Omnimetric Zenith [ABOZ] and Phyto-Tr) revealed that the ES ranged from high to poor among the lakes. The MPTI revealed that Lake Karagöl had a poor ES and Lake Kuğu had a moderate ES. A good ES was found in Lakes Borçka Karagöl and Sera, and Lake Uzungöl had a high ES. While MPTI, BCG and ABOZ provided consistent results, Phyto-Tr produced divergent outcomes. Correlation analysis highlighted strong relationships between MPTI, BCG, ABOZ and TP gradients. These findings underscore the importance of using multiple metrics to assess ecological health and highlight the influence of environmental factors on phytoplankton distribution and lake ES in different ecoregions. In addition, the findings of this study provide a scientific basis for ecosystem-based management and contribute to the conservation of freshwater resources in Türkiye.