Influence of hydrodynamic conditions on heavy metal distribution and ecological risk in freshwater sediments: a comparative study of reservoir and stream ecosystems.

This study provides a comparative and process-oriented assessment of heavy metal contamination in surface sediments across freshwater ecosystems in the Eastern Black Sea region (Türkiye), aiming to elucidate the role of hydrodynamic conditions and anthropogenic inputs in shaping metal distribution and ecological risk. Sediment samples were collected seasonally between December 2024-2025 from Muratlı Reservoir (lentic system) and two lotic systems, Arılı and Çağlayan streams, with four sampling stations in each ecosystem. Concentrations of Cu, Pb, Zn, Ni, As, Co, and Cr were determined using ICP-MS, and contamination was evaluated using geochemical indices and sediment quality guidelines. Metal concentrations exhibited pronounced spatial variability among the systems. Arılı Stream showed the highest accumulation levels, with concentration ranges of Cu (53.5-120.5 μg/g), Pb (27.5-55.5 μg/g), Zn (142.8-215 μg/g), Ni (27.2-46.5 μg/g), As (19.3-66 μg/g), Co (20.4-55.6 μg/g), and Cr (55.0-164 μg/g). In contrast, Çağlayan Stream exhibited elevated concentrations for Cu (55.3-117.4 μg/g), Pb (37.1-92.6 μg/g), and Zn (120.3-166 μg/g), while other elements remained within moderate ranges. Muratlı Reservoir showed lower but variable concentrations, with Cu ranging between 43.6 and 72.3 μg/g and Zn between 83 and 138 μg/g. Seasonal patterns indicated increased metal concentrations during summer and autumn.The integrated assessment identified As and Pb as the primary elements of concern, while Zn and Ni were secondary contributors with potential ecological implications. Overall, the findings demonstrate that contamination and ecological risks are system dependent. Comparison with sediment quality guidelines identified As and Pb as the primary ecological concerns, emphasizing the need for continuous monitoring, effective pollution control, and sustainable sediment management.