Functional Group Responses to Hydrological Disturbance and Environmental Gradients in Eastern Mediterranean Lakes (Türkiye)

Abstract

This study examines the effects of physicochemical variables on phytoplankton functional groups (FGs) in seven lentic ecosystems, including one natural lake (Akgöl) and six artificial water bodies comprising five reservoirs (Gezende, Alaköprü, Berdan, Bağbaşı, and Ermenek) and one pond (Sarıveliler), in the Eastern Mediterranean River Basin (Türkiye), representing Mediterranean and semi-arid climatic conditions. Phytoplankton and environmental data were collected seasonally (spring and autumn) during 2020–2021 from 18 sampling stations. Strong spatial and temporal heterogeneity was observed among lakes. The shallow, saline-influenced Akgöl Lake showed low functional diversity and dominance of benthic and tychoplanktonic diatoms (codon MP), associated with sediment resuspension and unstable mixing. In contrast, deeper stratified reservoirs (Gezende, Berdan, Ermenek) were dominated by motile dinoflagellates (codon L0), particularly in spring under stable, oxygenated conditions. Seasonal dynamics structured FG composition, with spring assemblages favoring mixing- and oxygen-adapted groups, whereas autumn assemblages shifted toward taxa tolerant of higher turbidity and organic enrichment. Redundancy analysis revealed that salinity, turbidity, suspended solids, and total organic carbon were the main drivers of FG distribution, while nutrients had comparatively weak explanatory power. Together, these variables define a clear mineralization–organic matter–turbidity gradient controlling phytoplankton structure across the basin. Mesotrophic functional groups dominated overall, although their relative contributions varied with local environmental conditions. The results demonstrate that phytoplankton FGs are reliable indicators of ecological status and spatial variability in Eastern Mediterranean lakes. Importantly, the system is structured by a pronounced hydrological degradation gradient driven by coupled salinity, organic matter, and turbidity dynamics, which emerges as the dominant organizing environmental framework. This highlights the need to integrate hydrological regulation, sediment dynamics, and organic matter processes with nutrient management under increasing anthropogenic and climatic pressures.

Keywords

• Water quality
• organic matter
• lake ecosystems
• functional groups

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