Mai Po Marshes is a sub-tropical estuarine wetland in Hong Kong, which is a complex, dynamic and unique ecosystem. The main objective of the present study is to explore heavy metal mobility in the sediments as a function of biogeochemical conditions in the aquatic environment in Mai Po Marshes. Samples of sediments and water were collected monthly from eight sites during July-September 1997. Heavy metal (Cd, Cr, Cu, Ni, Pb, Zn) concentrations in the sediments and their associations with aquatic physicochemical properties were examined. Aquatic biogeochemical processes appear to be different between landward and seaward sides. Heavy metal mobility seems to be closely associated with organic matter degradation on the landward side, while water quality and changes in redox conditions appear to be the major processes responsible for heavy metal mobility on the seaward side. At Mai Po Marshes, whereas organic enrichment benefits bird conservation as previous studies indicated, the results of this present study suggest that organic dynamics associated with heavy metal mobility and toxicity may also be taken into consideration for organic matter management.
