Metal Speciation (Cu, Zn, Pb, Cd) and Organic Matter in Oxic to Suboxic Salt Marsh Sediments, Severn Estuary, Southwest Britain

Pollutant metals (Cu, Pb, Zn and Cd) in Late Flandrian mudflat/saltmarsh sediments in the Severn Estuary are predominantly bound in the carbonate, Fe/Mn oxide and organic phases. Comparison of the oxic Rumney Formation with the suboxic Wentlooge Formation shows that redox conditions control iron cycling, and that this in turn controls trace metal associations. An important fraction of the trace metals present in the Fe/Mn oxide phase in oxic sediments (such as the Rumney Formation) is remobilised during iron reduction and reprecipitated in other phases such as authigenic carbonates (as in the Wentlooge). Since many metal pollutants are highly redox sensitive, a better understanding of the effects of redox on metal speciation in estuarine sediments is useful for management of the coastal environment.