Metal speciation (Cu, Zn, Pb) and organic matter in an oxic salt marsh, Severn Estuary, southwest Britain

Predominantly anthropogenic Cu, Zn, and Pb present in an approximately 100 yr old mud flat and salt marsh deposit at a high intertidal, oxic site are bound chiefly in the Fe---Mn oxide-hydroxide, organic and residual phases. The amount of each metal in the organic phase is significant and declines with increase in the age of the buried sediment, in harmony with the total amount of organic matter remaining. Application of a quantitative geochemical model provides evidence that those metals remobilized by the progressive oxic degradation of the organic matter do not swell the oxide phase also present in the deposit, but are free to be flushed back into the estuary.