The fate of crude oil on coastal wetlands, barrier islands and beaches is a key uncertainty in understanding the ultimate fate and impact of the Deepwater Horizon (DH) oil spill along the Gulf Coast. Barrier island and coastal wetland environments are among the most important and sensitive ecosystems, and yet oil and its effects are likely to be far more persistent in these environments than in high energy offshore environments. The spill demonstrated that we do not possess the ability to predict the behavior and effects of a large volume of oil that may be intact, emulsified or dispersed, entrapped on coastal beaches, or penetrated deeply into sensitive coastal marshes. For this spill, the vast majority of the oil reaching shore was in the form of a water-in-oil emulsion or mousse. As the emulsified oil approached the shoreline, it created several unique types of oil deposits, including small, spherical sand coated residues (SCRs) on the beach, tar mats in the nearshore environment, and emulsified oil pools on the surface of the marshes, mangroves and beaches. While the physical and chemical conditions that lead to emulsions are well understood (McLean and Kilpatrick, 1997; Xie et al., 2007), virtually no information exists on the fate, transport and remediation of emulsified oil. The contrast in shoreline natural recovery and active remediation requirements between dispersed oil, weathered liquid oil and emulsified oil is a key lesson of the DH spill and response. Making comparisons between fate, transport and recovery of these three oil "states" will be a unifying theme of the hypotheses and studies proposed by the team.
Pardue's laboratory has conducted studies on both the fate and effects of emulsified MC252 oil on the beach, mangroves and salt marshes at the Wisner Donation Land trust near Port Fourchon, Louisiana. This beach and dune system at Wisner is extremely dynamic, with wind, waves and tide continuously scouring and reforming the beach on top of the tidal 2 flats and relict deltaic and marsh deposits. All of these environments are critical habitat for hundreds of species of plants and animals, and form a vital protective buffer against storms, sea level rise, and salt water intrusion for inland areas. The Donation has granted us access to oiled areas for the purpose of this study. Detailed studies of the behavior, fate and effects of MC252 oil in impacted marsh environments are proposed, as well as research to develop active remedial strategies and understand how they can be employed to speed recovery.
Measurements and modeling efforts will include:
- the distribution of PAHs, alkanes and biomarkers (norhopanes) in marsh soils (time series)high resolution porewater PAH concentrations and flux (dialysis sampler; SPME; conventional);
- soluble nutrient and electron acceptor concentrations (dialysis samplers);
- microbial community structure analysis (DGGE; sequencing);
- stable isotope measurements on CO2 evolved from marsh surface (chambers and natural abundance MS of entrapped CO2);
- sediment oxygen demand measurement/diagenetic modeling;and
- serum bottle studies (id of limiting nutrient/electron acceptors)