Date of Award

1992

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

First Advisor

Donald Dean Adrian

Abstract

Laboratory studies and field measurements were conducted to quantify assimilative capacity of toxic organic contaminants in freshwater wetlands. Studies were conducted for hexachlorobenzene and naphthalene in a mineral-dominated bottomland hardwood forest and an organic matter-dominated freshwater marsh. In laboratory studies, sorption of hexachlorobenzene (HCB) in wetland soil and floodwater was strongly influenced by high levels of naturally occurring dissolved organic carbon (DOC). Organic matter-dominated wetlands (e.g., marshes) demonstrated no advantage over mineral-dominated wetlands (e.g., bottomland hardwood forests) for sorption of HCB due to partitioning in this DOC phase. Over the short-term, sorption of HCB was adequately described using a three-phase equilibrium model that included the DOC phase. Sorptive assimilation of HCB appears to be dependent on unique hydrological conditions that promote sediment-water exchange rather than any enhanced sorptive ability of wetland substrates, themselves. Sorption of naphthalene was greater in the freshwater marsh due to the increased fraction of organic carbon and the lower affinity of naphthalene for DOC. Small, but measurable, differences were observed in sorption partition coefficients between aerobic and high-DOC, anaerobic incubations. Reductive dechlorination of HCB was observed under low redox conditions ($\sim -$200 mV) in both wetland soils. Substantial degradation of HCB (50-60% in the bottomland hardwood soil; 90% in the freshwater marsh soil) occurred over a period of 18 weeks. Mineralization of naphthalene was rapid in the freshwater marsh and bottomland hardwood soil when aerobic, high redox potential conditions were present. No mineralization was observed under anaerobic conditions. Shapes of mineralization curves were dependent on substrate concentration and were well fitted using a three-half order kinetic model. An assimilation model was developed to describe removal of toxic organics in a conceptually simple wetland. External assimilation fluxes are volatilization, reaction (e.g., biodegradation), outflow and burial. Sensitivity analysis indicated that assimilation of hydrophobic compounds (e.g., HCB) is inhibited by high concentrations of DOC. Removal of compounds such as naphthalene is controlled by volatilization. The assimilation model is suited for several uses including estimating the assimilation capacity of wetlands for organic contaminants, testing various treatment or fate scenarios, and estimating the fate of new compounds entering wetlands.

Pages

207

Share

COinS