EFFECTS OF PHYSICAL-CHEMISTRY AND BIOTURBATION BY ESTUARINE MACROFAUNA ON THE TRANSPORT OF HYDROPHOBIC ORGANIC CONTAMINANTS IN THE BENTHOS

Effects of macrobenthos on hydrophobic organic contaminant (HOC) trans port during two seasons characterized by high (summer) and low (winter ) bioturbation were studied in the laboratory. HOC burial and loss fro m microcosms were followed in the presence and absence of macrofauna a fter the introduction of particle-associated polycyclic aromatic hydro carbons (PAHs) and polychlorinated biphenyls (PCBs) to the sediment-wa ter interface. During summer, HOC burial depths and modeled diffusive losses (D-L) increased with compound relative effective diffusivity (D (eff)), consistent with enhanced fluid transport rates due to macrofa una. Although more than 50% of HOC loss was independent of macrofauna, macrofauna-mediated processes had significant effects on the long-ter m (56 d) removal of the hydrophobic compounds TCB and BaP. A possible mechanism for this effect is direct particle resuspension by macrofaun a, which has been shown to enhance loss of materials from our experime ntal systems. During winter, macrofauna had little effect on HOC buria l but may have enhanced HOC retention. Thus, effects of macrofauna-med iated processes depend on HOC physico-chemistry as well as the tempora l phasing and duration of contaminant-biota interactions. Bioturbation has important implications for contaminant fate because macrofauna si gnificantly alter the distributions of HOCs near the sediment-water in terface.