The biogeochemical cycling of trace metals and oxyanions in marine sediments is primarily driven by the early diagenesis of organic material, though human activities can significantly disrupt these natural processes. Three stations in the Belgian Coastal Zone (BCZ) were chosen to investigate these impacts: W1 (affected by the disposal of dredged sludge), W2 (influenced by shipyard activities like boat hull blasting), and S1 (where the heavily polluted water from the Scheldt estuary mixes with the less polluted coastal seawater). Different from classic solid sediment phase analysis, analyses of total dissolved element concentrations (porewater extraction) and of dissolved labile element concentrations (passive sampling technique) were performed. Generally, total and labile dissolved element profiles in the porewaters are well correlated showing higher concentrations in March than in October when the redox potential is very low. Dumping of dredged sludge strongly lowered the pH levels in March, releasing large amounts of Fe and associated contaminants from the solid sediment phase. At the coastal station in the vicinity of the shipyards, elevated levels of dissolved Zn were detected in the sediment porewaters, while the highest dissolved Cu levels were found at the mouth of the Scheldt estuary. For the first time, R values, the ratios of labile element concentrations (passive sampling) to total dissolved concentrations (porewater extraction), were calculated every 2 cm in each sediment, reflecting the potential of the solid sediment phase to supply labile elements to the porewater.

sediment porewater, diffusive gradients in thin-films, anthropogenic impacts, biogeochemical cycling of trace metals and oxyanions, R-value profiles