Integrated Laboratory and Field Studies on Effects of Oil on Key Wetland Soil/Sediment Biogeochemical Processes

On April 20, 2010, the BP Deepwater Horizon (DWH) offshore oil platform experienced an explosion that triggered the largest marine oil spill in US history, resulting in the release of ~795 million liters of southern LA light sweet crude oil into the Gulf of Mexico. Approximately 7.9 million liters of dispersant, Corexit EC9500A, was used during the spill for remediation. We examined the effect of DWH crude oil and Corexit EC9500A, the dispersant used during the spill, on coastal Louisiana marsh soil microbial populations and processes. Surface soil samples were collected from an unimpacted salt marsh site proximal to areas that suffered light to heavy oiling in Barataria Bay, LA. The 1:10 ratio of crude oil:wet soil fully coated the soil surface, mimicking a heavy oiling scenario. Potential denitrification rates at the 1:10 oil:wet soil ratio, for weathered south LA light sweet crude oil, were 46 ± 18.4% of the control immediately after exposure and 62 ± 8.0% of the control following a two week incubation period. Denitrification rates of soil exposed to fresh crude oil were 51 .5 ± 5.3% of the control after immediate exposure and significantly lower at 10.9 ± 1.1 % after a 2 week exposure period. Microbial biomass nitrogen(N) values were below detection for the 1:10, 1:100 and 1:1,000 Corexit:wet soil treatments. Potentially mineralizable N correlated with microbial biomass with decreased activity for 1:10 and 1:100 Corexit:wet soil treatments. Potential denitrification rates after immediate exposure to Corexit:wet soil ratios of 0:10, 1:10, 1:100, 1:1,000, and 1:10,000 were below detection for the 1:10 treatment while the 1:100 was 7.6 ± 2.7% of the control and the 1:1,000 was 33 ± 4.3% of the control. The 1:10,000 treatment was not significantly different from the control. Denitrification rates measured after 2 weeks exposure showed the 1:10 treatment still below detection limit and the 1:100 was 12 ± 2.6% of the control. Results suggest that while both crude oil and Corexit impact denitrification, which is an important microbial process for water quality, Corexit is more detrimental at identical concentrations.

2010年4月20日，英国石油公司（BP）的“深水地平线”（Deepwater Horizon, DWH）海上石油钻井平台发生爆炸，引发美国历史上规模最大的海上溢油事故，约7.95亿升路易斯安那州南部轻质低硫原油涌入墨西哥湾。本次溢油治理期间共使用约790万升Corexit EC9500A分散剂。
本研究探究了本次事故中的DWH原油与Corexit EC9500A分散剂，对路易斯安那州沿岸沼泽土壤微生物种群及代谢过程的影响。研究人员从巴拉塔里亚湾（Barataria Bay）受轻度至重度油污影响区域附近的未受干扰盐沼点位采集表层土壤样本。以1:10的原油与湿土比例完全覆盖土壤表面，模拟重度油污场景。
针对该风化的路易斯安那州南部轻质低硫原油，采用1:10油土比时，处理后即刻测得的潜在反硝化（denitrification）速率为对照组的46±18.4%；经两周室内培养后，该速率回升至对照组的62±8.0%。而暴露于新鲜原油的土壤样本，处理后即刻的反硝化速率为对照组的51.5±5.3%，但经过两周培养后，该速率显著降至10.9±1.1%。
1:10、1:100及1:1000的Corexit与湿土配比处理组的微生物生物量氮（microbial biomass nitrogen, N）均低于检出限。潜在矿化氮（potentially mineralizable N）与微生物生物量呈正相关，1:10和1:100的Corexit-湿土配比处理组的活性显著降低。
处理后即刻检测的潜在反硝化速率显示，0:10（对照组）、1:10、1:100、1:1000及1:10000的Corexit-湿土配比中，1:10组未检出反硝化活性；1:100组的反硝化速率为对照组的7.6±2.7%；1:1000组为对照组的33±4.3%；1:10000组与对照组无显著差异。经过两周暴露后，1:10组仍未检出反硝化活性，1:100组的反硝化速率为对照组的12±2.6%。
研究结果表明，尽管原油与Corexit分散剂均会对作为维持水质关键微生物过程的反硝化作用产生负面影响，但在相同浓度配比下，Corexit的抑制效果更为显著。