Behavior of trace metals in the sediment pore waters of intertidal mudflats of a tropical wetland

Vertical profiles of dissolved Cd, Cr, Cu, Pb, Zn, Fe, and Mn in the sedime nt pore waters of the intertidal mudflats of the Mai Po and Inner Deep Bay Ramsar Sire of Hong Kong, People's Republic of China, were measured using t he polyacrylamide gel diffusive equilibration thin film (DET) technique. Th e ranges of concentrations of dissolved Cd, Cr, Cu, Pb, Zn, Fe, and Mn in t he pore water of the top 0 to 20 cm of sediment were 2.2 to 10.0 nM, 346.0 to 950.0 nM 243.8 to 454.8 nM, 23.2 to 51.2 mM, 39.8 to 249.5 mu M, and 13. 4 to 20.7 mu M, respectively. Enrichment of these trace metals was observed in the upper 0- to 7-cm layer. Profiles of conditional distribution coeffi cient, log(K-D), of the trace metals and results of multiple regression ana lysis have revealed that reduction of Mn (hydrous) oxides was the major rem obilization mechanism for Cd, Cr, Cu, Pb, and Zn in the mudflats. Benthic d iffusive fluxes of these trace metals from the mudflats were also estimated on the basis of the concentration gradients of trace metals between surfac e sediments and the overlying water column. The magnitude of the estimated diffusive fluxes followed the order Zn > Cr > Cu > Pb > Cd.