Impacts of Lake Surface Area on Phytoplankton Community Dynamics and Ecological Status Across 70 Lentic Systems in Türkiye

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ABSTRACT In this study, phytoplankton communities and environmental variables in 70 lentic systems in Türkiye were analysed using samples collected from 2017 to 2019. The objective was to evaluate how lake surface area (SUA) affects phytoplankton assemblages. The lentic systems were categorized into three SUA groups: I (< 50 ha), II (50–500 ha) and III (> 500 ha). The results showed that both species composition and dominant species varied with SUA. Some species preferred larger SUAs and higher SUA optima values. Phytoplankton biovolume increased with SUA, particularly in Group III, which had the highest total phosphorus (TP). Species richness (alpha diversity) followed a unimodal distribution, peaking in Group II, whereas total species richness (gamma diversity) decreased with increasing SUA. The distribution of gamma diversity among different phytoplankton groups varied across the SUA categories, reflecting their distinct responses to SUA. The PHYTO‐TR index proved to be a more precise tool for assessing the ecological quality of lentic systems, based on TP and phytoplankton biovolume. Groups I and II had a higher proportion of high‐quality lentic systems. Parameters such as temperature (T), electrical conductivity (EC), alkalinity (ALK), Secchi depth (SD) and TP were significant factors influencing phytoplankton distribution, composition, biovolume and both alpha and gamma diversity, as well as the overall ecological quality. Although the effect of SUA, which correlates with T, ALK, EC and SD, on phytoplankton is largely indirect through these parameters, there was also evidence of a direct effect because of the varying responses of different phytoplankton groups to SUA.