ASSIMILATION OF HYDROPHOBIC CHLORINATED ORGANICS IN FRESH-WATER WETLANDS - SORPTION AND SEDIMENT WATER EXCHANGE

In laboratory studies, sorption of hexachlorobenzene (HCB) in wetland soil and floodwater was strongly influenced by high levels of naturall y-occurring dissolved organic carbon (DOC). Organic matter-dominated w etlands (e.g., marshes) containing high concentrations of DOC demonstr ated no advantage over mineral-dominated wetlands (e.g., bottomland ha rdwood forests) for sorption of HCB due to partitioning in this DOC ph ase. Sorption of HCB was described adequately using a three-phase mode l that included the DOC phase. However, partition coefficients in the bottomland hardwood soil were time-dependent. This time-dependent phen omena was not observed in the freshwater marsh soil. Sorptive assimila tion of organic compounds in wetlands appears to be dependent on the u nique hydrological conditions that promote sediment-water exchange and accretion rather than any enhanced sorptive ability of wetland soils themselves.