The Effect of Pore Water Chemistry on the Biodegradation of the Exxon Valdez Oil Spill

Abstract

Knowledge of the oxygen and nutrient concentra- tions in an oil-contaminated Prince William Sound (PWS) beach is important for understanding of the oil persistence over two decades after the Exxon Valdez spill. It was tradi- tionally believed that there was enough oxygen in the conta- minated shorelines to sustain aerobic microbial metabolism of oil and that nutrients were the major factors limiting oil biodegradation. In the present study, we analyzed the oxy- gen and nutrients levels in both clean and oily areas on a PWS beach that was heavily contaminated by the Exxon Valdez oil spill. We found that the level of nitrogen and phosphorous were 0.454 mg-N L −1 and 0.033 mg-P L −1 , respectively, which is not sufficient to fully support micro- bial growth, confirming that nutrient concentration was a major factor limiting oil transformation by biological ways. We also observed that the oxygen level varied from higher than 3 mg L −1 in the clean wells to about 1 mg L −1 (near anoxic level) in the oily wells. In addition, the lowest nitrate levels were observed at the oily wells. Altogether, these re- sults suggest that the low level of efficient electron acceptors (oxygen and nitrate) detected at the oily spot is responsible for slow and potentially inefficient biodegradation of the oil.