The initial research of the Coastal Waters Consortium (CWC) demonstrated that what were thought to be stable oil biomarkers were not stable, that there were multiple oilings 100+ m into the marsh, and that the oiling varied by an order of magnitude within 20 m along the shoreline. While some hydrocarbon components will reach background levels in about five years, other polycyclic aromatic hydrocarbons (PAH) analytes increased over two years, and some of the more volatile hydrocarbons remain buried, continue to impact marsh organisms, and may take a decade before their influence diminishes below significance, if then. The oiled areas may, therefore, act as an "ecological sink" that maintains low population levels for years. Some greenhouse gas emissions from marshes increased, whereas others did not. A wide variety of marsh producers and consumers, including insects, spider, crabs, fish, and birds, were affected. Shoreline erosion of salt marsh vegetation intensified, microbial communities were altered, and populations of key marsh organisms were suppressed. CWC researchers obtained some of the first ever biogeochemical measurements (greenhouse gases) and concurrent microbial diversity estimates for oiled and unoiled marsh ecosystems. The impacts on marsh nekton populations, unlike individual fish, were minimal. We conclude from these results, and others, that there will be continued shifts in the abundance and composition of marsh producers (plant, algae, phytoplankton, and microbial communities) and consumers (invertebrate, fish, birds, and mammals) as the marsh recovers from the impacts of PAH toxicity. There is, therefore, an ecosystem-wide legacy of the Deepwater Horizon (DWH) oil spill that extends beyond three years. This conclusion supports the CWC goal to provide a better understanding of the fate and continued degradation of oil, its influence on food web structure, how the resulting shifts influence populations, individuals, and ecosystem functions during the recovery phase, and the interaction of oiling impacts with the other ecosystem stressors. The CWC will investigate the impacts of the DWH oil spill as the signal:noise ratio continues to diminish and use its extensive pre-spill, 2010, and CWC GoMRI post-spill sampling to the best advantage and in a way that builds long-term data sets that benefit many purposes.
Key hypotheses / assumptions are:
- Significant amounts of oil are redistributed from estuarine bottom to marsh during storms, and that the amount is declining, though still influential in the next three years.
- Habitat loss and food web alterations will become more consequential to fisheries, birds, and marsh-dependent organisms than oil toxicity as 'recovery' or relative stability returns.
- Behavioral changes may lead to population and community level effects through changes in trophic interactions that propagate up or down trophic levels, and through diminished growth, survival and/or reproductive fitness that becomes manifested in subsequent generations.
- Shoreline erosion is permanent.
- Most of the significant impacts on sediments, birds, insects, marsh plants, and fish observed within the first three years will diminish in proportion to the concentration of PAH - which is declining over decades.
- Microbial genetics analyses offer insightful and rapidly accessible information for ecosystem stress indices for communities and ecosystems.
CWC research efforts in support of testing the hypotheses include subtasks on: analytical support and oil fate and transformation, modeling + model support, geomorphological framework and the consequences of oiling, wetland biogeochemistry/microbial ecology, microbial biogeochemistry/ genetics, phytoplankton community, intertidal microbenthic flora and subtidal infauna, insects and spiders, marsh fish, terrestrial vertebrates, PAHs in Common Loons, tracing carbon flow and food web structure in coastal marshes, connectivity and structure of marsh invertebrates, behavioral responses of organisms to oil, and manipulative experiments in replicated mesocosms. The results of these inquiries are intended to yield scientific advances about these ecosystems, even when there are no oil impacts.