ABSTRACT
Use and transport of petroleum products can result in serious contamination of freshwater habitats via leakage, spills, aerosols, and runoff. Little development of bioremediation strategies has occurred for enhancing degradation of petroleum products in situations involving contamination of freshwater wetland ecosystems. The objective of this study was to investigate different inorganic mineral nutrients for their ability to enhance biodegradation of crude oil in contaminated wetlands on a microcosm scale. Aquaria of 10-gallon capacity, filled with wetland soil and planted with species of emergent wetland plants, were used to simulate natural wetlands. Two levels of water coverage were studied: (1) water level even with soil surface, and (2) water level 10 cm above the soil surface. Six treatments were evaluated in duplicate for each water level: unoiled, no-nutrient control; oiled + no nutrient control; oiled + nitrate addition; oiled + nitrate + phosphate addition; oiled + ammonia addition; and oiled + ammonia + phosphate addition. Thus, 24 aquaria were set up for each sampling event (0, 2, 4, 8, 16, and 32 weeks) totaling 144 aquaria. Nutrients were applied once each week. Nitrate, ammonia, dissolved oxygen, pH, temperature, and conductivity were measured before and after nutrient addition. Biodegradation was tracked by GC/MS analysis of hopane-normalized crude oil components from the sacrificed aquaria over the 32-week experimental period. Results indicated that: (1) the rates of biodegradation of the alkanes and PAHs (polycyclic aromatic hydrocarbons) were higher for all treatments in the high-water level microcosms compared with the low-water level microcosms; (2) the highest rates of alkane and PAH degradation were measured in the high-water level microcosms receiving nitrate and phosphate; (3) the treatments with nitrate and phosphate showed nearly a 90% reduction of alkanes and a 50% reduction of PAHs as compared to nearly a 50% reduction of alkanes and 40% reduction of PAHs by the oil with no nutrients control for the high-water level; (4) the nitrate and phosphate addition treatments, for both water levels, showed good plant growth and the highest plant and root densities as compared to the other treatments. This information is being used in the design of a mesoscale experiment as part of the second phase of this study.