There is a spatial difference as to heavy metal mobility and its associations with the local aquatic biogeochemical processes at Mai Po Marshes. Organic matter decomposition seems to be the major process that determines heavy metal mobility at the landward side, while redox condition dynamics at the seaward side appear to be the controlling factor for heavy metal mobility. It is suggested in the chapter that the uneven distribution of mangrove trees in gei wais may determine the organic matter (litter) input to the sediments and water temperature. Sediment resuspension and changes in redox conditions seem to be typical characteristics in estuarine systems, and sites closer to the coast seem to have more dramatic sediment resuspension and redox change in gei wais at Mai Po Marshes. Copyright © 2004 Elsevier B.V. All rights reserved.