The significance of sediment metal concentrations in two eroding Essex salt marshes

Two eroding salt marshes, at Dengie and Little Oakley, situated along the Essex coast (UK) were monitored for concentrations of As, Ca, Cd, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, Pb, Se and Zn in bulk sediment and in the < 64 μm fraction. In conjunction with sediment metal concentrations reported for five other Essex salt marsh sites, natural background levels for this area have been derived. These highlighted that As, Cd, Hg, Pb and Zn were the main anthropogenic contaminants in the Essex salt marsh sediments. There was a disparity between the metal concentrations found in the vegetated marsh and mud flat sediments taken from Dengie, and for Cr, Fe and Ni this was entirely attributable to particle size distribution rather than anthropogenic inputs. Sediment metal concentrations from a net accreting salt marsh at Stiffkey (North Norfolk), which is remote from industrial metal inputs, were within similar ranges to the Essex salt marshes.