Hypersaline Pore Water in Gulf of Mexico Beaches Prevented Efficient Biodegradation of Deepwater Horizon Beached Oil

The
2010 Deepwater Horizon (DWH) blowout released 3.19 million
barrels (435 000 tons) of crude oil into the Gulf of Mexico.
Driven by currents and wind, an estimated 22 000 tons of spilled
oil were deposited onto the northeastern Gulf shorelines, adversely
impacting the ecosystems and economies of the Gulf coast regions.
In this work we present field work conducted at the Gulf beaches in
three U.S. States during 2010–2011: Louisiana, Alabama, and
Florida, to explore endogenous mechanisms that control persistence
and biodegradation of the MC252-oil deposited within beach sediments
as deep as 50 cm. The work involved over 1500 measurements incorporating
oil chemistry, hydrocarbon-degrading microbial populations, nutrient
and DO concentrations, and intrinsic beach properties. We found that
intrinsic beach capillarity along with groundwater depth provides
primary controls on aeration and infiltration of near-surface sediments,
thereby modulating moisture and redox conditions within the oil-contaminated
zone. In addition, atmosphere–ocean–groundwater interactions
created hypersaline sediment environments near the beach surface at
all the studied sites. The fact that the oil-contaminated sediments
retained near or above 20% moisture content and were also eutrophic
and aerobic suggests that the limiting factor for oil biodegradation
is the hypersaline environment due to evaporation, a fact not reported
in prior studies. These results highlight the importance of beach
porewater hydrodynamics in generating unique hypersaline sediment
environments that inhibited oil decomposition along the Gulf shorelines
following DWH.