Impact of sediment resuspension on near-bottom mercury dynamics: Insights from a Baltic Sea experiment

Marine sediments are major sources of legacy pollution, capable of releasing toxic mercury (Hg) into the water column when disturbed. This study evaluated Hg remobilization from surface sediments during resuspension events by examining sediment properties, Hg concentrations, and speciation. Research was conducted in the southern Baltic Sea, representing diverse environmental conditions and human impacts. The findings showed that sediment resuspension was the primary driver of Hg remobilization, with diffusion flux playing a minimal role. Both dissolved and particulate Hg were released almost immediately after resuspension, with elevated concentrations persisting long enough to be transported beyond the disturbed area. The diffusion of dissolved Hg was enhanced by labile Hg fractions in the sediment, with reducing conditions and high organic matter content further promoting this process. Particulate Hg remobilization was influenced by sediment characteristics, particularly bulk density, which affected resuspension susceptibility and dispersion of suspended matter. The total Hg concentration and labile organic-bound Hg fractions also significantly influenced particulate Hg release. These results highlight the importance of sediment properties in managing Hg-contaminated sites and have implications for environmental protection and marine operations planning.