The　biogeochemical　cycle　of　trace　metals　and　oxyanions　in　marine　sediments　is　mainly　controlled　by　early　diagenesis　of　organic　material,　but　anthropogenic　activities　such　as　dumping　of　dredged　sludge　or　shipyard　activities　can　strongly　perturb　these　natural　processes.　Therefore,　the　impact　of　dumping　of　dredged　sludge,　shipyard　activities　such　as　blasting　of　boat　hulls　and　the　mixing　of　polluted　Scheldt　estuary　water　with　less　polluted　coastal　water　on　the　mobilization　of　trace　metals　and　oxyanions　in　the　sediments　was　studied　in　the　pre-　and　post-bloom　period　(March　and　October)　in　Belgian　Coastal　Zone　(BCZ).　Vertical　profiles　of　total　and　labile　dissolved　trace　element　concentrations,　dissolved　sulfide,　pH　and　redox　potential　were　assessed　in　sediment　porewaters.　Generally,　total　and　labile　dissolved　element　profiles　in　the　porewaters　are　well　correlated,　showing　higher　concentrations　in　March　when　the　redox　potential　is　lower　and　sulfide　concentrations　higher.　Low　pH　levels　were　documented　together　with　high　amounts　of　Fe　and　associated　elements　in　March　at　the　dumping　station.　At　the　coastal　station　in　the　vicinity　of　the　shipyards,　sediment　porewaters　are　enriched　in　dissolved　Zn　while　at　the　mouth　of　the　Scheldt　estuary　the　highest　dissolved　Cu　levels　were　found.　Theoretical　calculations　with　Visual　MINTEQ　confirm　the　increased　Fe　and　associated　element　concentrations　in　March　(lower　pH)　and　the　lower　metal　concentrations　in　October　(lower　Eh).　R　values,　ratio　of　labile　dissolved　to　total　dissolved　concentrations,　reflect　the　potential　of　the　solid　sediment　phase　to　supply　labile　elements　to　the　porewater.　They　were　lowest　for　Cu　and　highest　for　V.　This　study　showed　that　anthropogenic　activities　in　the　BCZ　such　as　dumping　of　dredged　sludge　and　blasting　of　boat　hulls　have　a　serious　impact　on　the　levels,　distribution　and　bioavailability　of　contaminants　in　the　sediments,　which　may　form　a　real　threat　to　the　benthic　ecosystem.