The Deepwater Horizon (DWH) oil spill exposed the nation’s largest and most productive wetland-estuary, the Mississippi River Delta coastal wetland ecosystem, to an unprecedented level of oil contamination and potential damage. The coastal marshes support a host of environmental and economic services that depend on a healthy, well-functioning plant-soil-microbial complex to drive the food web base. For ~7 years, the PI’s team has monitored the effects of the DWH oil spill in Louisiana salt marshes through 16 field-based data collections that quantify the impacts and recovery of a broad array of flora, fauna and microbes. Continuation of this research in heavily-oiled shorelines where marsh plants that serve as foundation species suffered severe mortality is critical to assessment of coastal marsh recovery, which to-date is incomplete, and to a better understanding of marsh resiliency to oil contamination. Also, the PI and team have identified highly polar, persistent oil transformation products derived from marsh sediments with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) within the first 4 years after the spill. Thus, the current proposal will (1) document and catalogue the decade-long impact of DWH oil on the coastal marsh plant-soil-microbial complex; (2) quantify rates and controls of long-term recovery; (3) catalogue oil transformation compounds detected in oiled salt marsh sediments up to 10 years after the spill and determine their toxicity; and (4) identify potential correlation between vegetation, microbes and transformed oil compounds in oiled salt marshes. It supports GoMRI theme 2: chemical evolution and biological degradation of oil and subsequent interaction with coastal marshes, and 3: knowledge of environmental effects of oil on marshes and the science of ecosystem recovery.
Oil spills can impact the structure, function, resilience and sustainability of coastal wetlands. Previous and ongoing GoMRI research by the PI and team identify several impacts from the Macondo oil spilled in Louisiana’s coastal wetlands, and subsequent recovery. Effects in marshes highlight recovery differences due to oiling intensity and species-specific responses. Specifically, moderately oiled marshes exhibit recovery of dominant plant species Spartina alterniflora within 9 months, yet Juncus roemerianus did not recover until ~3 years. In addition, benthic microalgae, invertebrates, and soil microbes were severely affected but recovered concurrently with vegetation. Areas that received heavy oiling, however, experienced a near complete kill of marsh vegetation, significantly reduced benthic microalgae and fauna, and decreased bacterial diversity. To date, Juncus recovery remains incomplete in heavily oiled areas, and vegetation structure has shifted from a Juncus–Spartina community to predominantly Spartina. This transition has greatly reduced marsh productivity, slowed some invertebrate and microbe recovery, and exposed areas to potential erosion. Oil degradation and oxidation in sediments occur in stages. An initial evaluation of oil transformation products indicates heavily-oiled sites have a lower abundance of highly oxidized transformation products than moderately oiled sites, which suggests heavy oil contamination hinders microbial activity. It is hypothesized that heavily-oiled sites are dominated by single-stage oxidation compared to moderately-oiled sites that display different oxidation signature that could be attributed to differences in the microbial community structure.
The combined research expertise of the PI and team in oil impacts on wetlands, the impact of the DWH spill specifically, and oil chemistry highly qualify the team to conduct the proposed research. Collectively, this group has published more than 50 refereed scientific papers on oil spill science; with 14 publications and 8 manuscripts in review on the DWH spill. The ~7-year database on DWH impacts and recovery in coastal salt marshes provides a catalogue to assess long-term resiliency and sustainability. Based on the preliminary characterization of oil transformation, oxidation in the sediments remains incomplete after 4 years and requires a comprehensive study on the symbiotic relationship between hydrocarbon transformation and microbial community. The current proposal emphasizes the ecological assessment of plant structure and function, marsh integrity and interactions in the plant-soil-microbe complex, a combination of cultivation-based and molecular-based biological analysis of microbial communities, and molecular-level characterization of oil chemical functionalities by ultrahigh resolution FT-ICR MS that cannot be identified by any other analytical technique. This proposed research will create a decade-long assessment record, and provide comprehensive integration of petroleum compound evolution and long-term recovery of oil impacted coastal wetlands.