Chapter 16 - Assessing the Increase in Background Oil–Contamination Levels Along Alabama's Beaches Resulting From the Deepwater Horizon Oil Spill

Abstract

The explosion of the Deepwater Horizon (DWH) oil drilling rig resulted in widespread contamination of Alabama's white sandy beaches. These beaches continue to be impacted by the various forms of oil spill residues that were formed from the DWH oil. We review published literature and several federal cleanup response reports to develop a set of hypotheses that are broadly used to describe the DWH oil spill–related contamination problems and their impacts on Alabama's beaches. We later test the validity of these hypotheses based on field-scale observations and several recently published datasets. Based on the results of this study, we make the following conclusions: (1) the current background oil–contamination levels are much higher than the relatively low (in some cases, negligible) background levels that existed prior to the DWH oil spill; (2) virtually all of the visible oil spill residues currently deposited along the Alabama shoreline, in the form of fragile, brownish, sticky tar balls and tar patties, originated from the DWH oil spill; and (3) several higher molecular weight PAHs, such as chrysene and its alkylated homologs, trapped in DWH oil spill residues are degrading at a much slower rate than they were prior to the oil being submerged near the shoreline; and it is highly likely that these contaminants will remain in the nearshore environment for an extended period of time. These conclusions were based on our analysis of the data collected from Alabama beaches and more field studies are needed to test their validity to other Gulf of Mexico beaches. Long-term monitoring data are not available to evaluate the changes in background oil levels occurring along the Alabama shoreline, and therefore future research efforts should conduct well-organized long-term surveys to capture both temporal and spatial variations in oil deposition levels. Future studies should also focus on developing rational metrics that can help quantify background oil levels and track its seasonal variabilities. Finally, the biological and ecological implications of the increases in background oil levels that resulted from the DWH oil spill are presently unknown; more biological studies are needed to better understand these implications.