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Carbon oxidation in intertidal wetland sediments
xvii, 266 leaves : illustrations ; 28 cm.
The geochemistry associated with the decomposition of natural and anthropogenic carbon sources and the use of alternative terminal electron acceptors as potential oxidants for crude oil components were investigated in this research. Long-term continuous monitoring techniques and discrete sampling were employed before, during, and after the controlled application of crude oil at the San Jacinto Wetland Research Facility, to determine the oxidative status of incoming/outgoing surface water and of vegetated and unvegetated sediments as a function of tidal activity, daily and seasonal cycles, and petroleum contamination. Primary production oxygenated surface waters by day, while continued heterotrophic activity depleted oxygen throughout the night. Seasonally, dissolved oxygen was inversely correlated with temperature and is attributed to increased heterotrophic activity in underlying mud flats during the hot, summer months compared to colder, winter months. In comparison to vegetated sediments that were dominated by Alternanthera philoxeroides, unvegetated sediments were more rapidly depleted of oxygen and iron oxides resulting in the accumulation of reduced aqueous and solid sulfides. Anaerobic incubation of sediment fractions revealed decreasing rates of carbon oxidation with depth from the surface that was accounted for by microbial reduction of Fe(III) (70%), from oxides and clays, and sulfate (30%), compared to sterilized sediments with negligible carbon mineralization. Laboratory incubations of crude oil inoculated with sediment from the field site demonstrated alkane and PAH degradation under aerobic, iron-reducing, and sulfate-reducing conditions. A steady-state model was developed to recreate the geochemical profiles observed during sediment analysis and ascribed organic carbon oxidation to the sequence, O₂ -> NO₃⁻ -> Mn(IV) -> Fe(III) -> SO₄²⁻ -> CO₂. Unvegetated sediments were calculated as 7, 1, <1, 4, 88, and 0%, respectively. Vegetated sediments exhibited different contributions: 19, 1, 5, 67, 9, and 0 %, respectively. The results indicate that competent populations of hydrocarbon degraders exist in wetland sediments and metabolize crude oil components under a variety of terminal electron accepting conditions. A. philoxeroides transports oxygen to the root zone and promotes the oxidation of spent terminal electron acceptors. Therefore, phytoremediation could serve to hasten the remediation of oil-contaminated matrices by maintaining a reservoir of Fe-oxide and sulfate to which hydrocarbon degraders can couple their metabolism.
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Includes bibliographical references (leaves 202-222).