Metal distribution during diagenesis in the contaminated sediments of Dulas Bay, Anglesey, N. Wales, UK

The Tessier sequential extraction procedure was applied to discrete layers from 9 sediment cores from Dulas Bay, Anglesey. Results provide data on the chemical association of heavy metals (Fe, Mn, Cu, Zn, Cd, and As with major) sedimentary phases, and provide information on changes in metal partitioning associated with the changing physico-chemical conditions encountered during burial. Extremely high concentrations of heavy metals were recorded (e.g. Zn 3000 μg g−1, Cu 2000 μg g−1) and resulting depth profiles clearly indicate the differential behaviour of metals during diagenesis where, with increasing depth, Fe, Mn and Cu become increasingly associated with sulphide phases. Substantial changes in porewater concentrations indicate zones of preferential mobilisation due to sharp alterations in physicochemical conditions. All metals are involved in processes of post depositional diagenetic cycling driven by organic matter degradation and O2 utilisation in thermodynamically favoured sequence, Fe and Mn oxide and oxyhydroxide dissolution act as controlling variables leading to zones of solid phase metal enrichment. Phase equilibria have been calculated to elucidate observed solid phase partitioning at the redox boundary and processes of subsurface sulphide mineral formation.