Project Overview

Summary:

     Drs. Scott Zengel and Sean Graham at Nicholls State University (NSU) were awarded an RFP-VI grant at $541,657 to conduct the RFP-VI project titled, “Meta-analytic synthesis of long-term wetland impacts, recovery, and resilience following the Deepwater Horizonoil spill”.  The project consisted of 4 other institutions (Atkins North America, Inc., Louisiana State University, Research Planning, Inc., and Virginia Institute of Marine Science.);  1 principal investigator (Dr. Zengel, formerly Dr. Graham), 3 co-PIs (Drs. Sean Graham, John Fleeger, Irving Mendelssohn); 2 research scientists (Donald Deis, David Johnson); 1 post-doctorate (Alexander Ameen); and 4 research staff members (Jennifer Weaver, Zach Nixon, Lauren Szathmary, and Hal Fravel).

     The Deepwater Horizon (DWH) oil spill was the largest marine oil release to date in US waters and ranks among the largest worldwide. Over 2,100 km of Gulf of Mexico shorelines were exposed to DWH oiling, with an unprecedented potential for environmental damage. Scores of individual studies and reports have described the impact of the DWH oil spill on wetland vegetation and benthic organisms in the Gulf of Mexico, including over a dozen studies from the current proposal team. While results to date generally indicate that recovery is occurring but not yet complete, individual studies by themselves do not create a complete picture of DWH impacts, and in some cases findings and conclusions are unclear or contradictory. As such, a clear understanding of the ecosystem, community, and population effects can be difficult to discern, even for large spills such as the DWH. Hence, a synthesis of results was needed to provide a more comprehensive understanding of marsh degradation and recovery following the DWH spill. Therefore, the overall goal of this proposed research was to assess the long-term impacts of the DWH spill using a broader, collaborative approach that includes meta-analytic and literature review synthesis of results across multiple data sets such as data from GoMRI, the Natural Resource Damage Assessment (NRDA), as well as other published and unpublished studies.

     Members of this project team have previously conducted similar meta-analyses and literature syntheses to evaluate DWH impacts and recovery for two groups of coastal wetland macroinvertebrates (fiddler crabs, Uca species and marsh periwinkles, Littoraria irrorata). In both cases, new, interesting, and more robust interpretations emerged from the analysis of multiple data sources across wider geographies and longer time frames, answering questions that could not be addressed by individual studies alone. This project proposes to further apply similar meta-analytic approaches and/or literature review to synthesize coastal wetland oiling impacts and recovery across a broader range of ecosystem response variables, such as coastal wetland plants, benthic invertebrates and infauna, and shoreline erosion.

     Overall, the results from this project provide a more comprehensive understanding of the factors that control impacts, recovery, resilience, and sustainability of the wetland vegetation-soil-benthic complex. Results from this work also inform current and future response, damage assessment, and restoration decisions for oiled coastal wetlands by providing integrated information of critical importance to understanding the pace of oil-spill recovery through data integration from various sources; scientific synthesis across themes; and overarching scientific products that exploit the scientific legacy GoMRI. In particular, this proposed research supports GoMRI Research Theme 3: environmental effects of spilled oil on wetlands, marshes, and organisms; and the science of ecosystem recovery, while also directly supporting the continuation of previously designated research themes and topics that have emerged through GoMRI.

Research Highlights

     The work of this research team resulted in 18 presentations and posters at professional conferences to date, 3 peer-reviewed publications to date, 8 outreach products and activities, and 5 datasets submitted to the GoMRI Information and Data Cooperative (GRIIDC), which are available to the public. Five (5) additional manuscripts are in preparation, under peer-review, or in revisions with journals, and other manuscripts may be forthcoming. This research team is also engaged in ongoing leadership and participation in the GoMRI Core 3 Wetland Synthesis Working Group, developing an overall synthesis of coastal wetland impacts and recovery, with a planned peer-reviewed synthesis publication or publications expected in the next few months. Significant outcomes of their research (all related to GoMRI Research Theme 3) are highlighted below.

Macroinfauna Responses and Recovery Trajectories after an Oil Spill Differ from those Following Saltmarsh Restoration. Abstract: Given the severity of injuries to biota in coastal wetlands from the Deepwater Horizon oil spill (DWH) and the resulting availability of funding for restoration, information on impacted salt marshes and biotic development of restored marshes may help inform marsh restoration planning in the near term and for future spills. Accordingly, we performed a meta-analysis to model a restoration trajectory of total macroinfauna density in constructed marshes (studied for ~30 y), and with a previously published restoration trajectory for amphipods, we compared these to recovery curves for total macroinfauna and amphipods from DWH impacted marshes (over 8.5 y). Neither total macroinfauna nor amphipod density in constructed marshes consistently matched reference levels before 20 y, yet in heavily oiled marshes recovery occurred by 4.5 y post spill (although it is unlikely that the community fully recovered). These differences were probably due to initial conditions (e.g., higher initial levels of belowground organic matter in oiled marshes) that were more conducive to recovery as compared to constructed marshes. Furthermore, we found that amphipod trajectories were distinctly different in constructed and oiled marshes as densities at oiled sites exceeded that of reference sites by as much as 20x during much of the recovery period. Amphipods may have responded to the rapid increase and high biomass of benthic microalgae following the spill. These results indicate that biotic responses after an oil spill may be quantitatively different than those following restoration, even for heavily oiled marshes that are denuded of vegetation. Our dual trajectories for oil spill recovery and restoration development for macroinfauna should help guide restoration planning and assessment following DWH and for restoration scaling for future spills.

Legacy Effects of Hurricane Katrina Influence Marsh Shoreline Erosion following the Deepwater Horizon Oil Spill. Abstract: Disturbance interactions occur when one perturbation influences the severity and perhaps the baseline state of succeeding disturbances. Natural and anthropogenic disturbances are frequent in dynamic coastal ecosystems and can often be linked. We evaluated potential for disturbance interactions associated with the 2010 Deepwater Horizon (DWH) oil spill, which was preceded by disturbance from Hurricane Katrina in 2005, by quantifying marsh shoreline retreat across both events. Our goal was to determine the degree to which Hurricane Katrina altered baseline rates of erosion prior to the DWH spill. We quantified erosion rate and fetch from aerial images of northern Barataria Bay, Louisiana marsh shorelines classified as reference, moderately-oiled, and heavily-oiled over three pre-spill time periods (1998–2004, prior to Hurricane Katrina; 2004–2005, during Katrina; 2005–2010, post-Katrina but pre-oil spill) and a post-spill period from 2010 to 2013. Prior to Hurricane Katrina, marsh shoreline erosion rates were low (from 0.38 to 1.10 m yr−1). In contrast during Hurricane Katrina (2004–2005), erosion increased by 661% and 756%, respectively, for shorelines that would subsequently become moderately and heavily-oiled; reference shoreline erosion increased by 59%. These high erosion rates were associated with increased fetch and higher wave action due to loss of protective geomorphic features such as small islands and spits and persisted during the post-Katrina/pre-spill period of 2005–2010 (0.62, 1.38, and 2.07 m yr−1 for reference, moderately, and heavily oiled shorelines, respectively). Erosion rates increased modestly after the DWH event (reference = 1.13 m yr−1, moderate oiling = 1.45 m yr−1; heavy oiling = 2.77 m yr−1), but not significantly, compared to the post-Katrina period. Consequently, we could not detect a post-spill increase in marsh shoreline erosion. Rather, we concluded that Hurricane Katrina reset the erosion baseline, thereby connecting the two disturbances, and was the major driver of marsh shoreline erosion at our research sites during the study period.

What Promotes the Recovery of Saltmarsh Infauna after Oil Spills? Abstract: Many factors influence the rate at which biotic communities recover from environmental disasters, and a thorough understanding of these factors is needed to formulate effective mitigation strategies.  The importance of foundation species, soil environmental quality, and benthic microalgae to the long-term recovery of the saltmarsh infaunal community following the 2010 Deepwater Horizon oil spill was examined in northern Barataria Bay, Louisiana from 2011–2016.  The community of 12 abundant taxa of meiofauna and juvenile macroinfauna began to rebound from oiling in < 2 years but did not fully recover after 6.5 years.  The pace and intensity of recovery of nematodes, copepods, most polychaetes, tanaids, juvenile bivalves and amphipods was significantly and positively related to the recovery of Spartina alterniflora and benthic microalgae.  However, total petroleum hydrocarbon concentrations remained elevated over time, and live belowground plant biomass, bulk density, dead aboveground plant biomass, and live aboveground biomass of Juncus roemerianus were not resilient, indicating that soil quality at oiled sites was insufficient to foster the recovery of the infaunal community as a whole.  Recovery of the kinorhynch Echinoderes coulli, the polychaete Manayunkia aestuarina, ostracods, and juvenile gastropods was suppressed in association with these factors.  Foundation species enhance saltmarsh infaunal recovery in the short term by influences associated with habitat modification and over the longer term by improving soil quality.  Therefore, efforts to enhance the recovery of foundation species (e.g., by plantings) should benefit the recovery of benthic primary producers and consumers after oiling in salt marshes.

Publications in development:  Once published they will be entered into the GoMRI Research Information System (RIS)

• Multiple Stressors and Marsh Shoreline Erosion Following the Deepwater Horizon Oil Spill
• Recovery of the Salt Marsh Periwinkle (Littoraria irrorata) Nine Years after the Deepwater Horizon Oil Spill: Size Matters
• A Macroinfaunal Ecosystem Engineer May Facilitate Recovery of Benthic Invertebrates and Accompanying Ecosystem Services after an Oil Spill
• Meta-Analysis of Salt Marsh Vegetation Impacts and Recovery, Synthesis Following the Deepwater Horizon Oil Spill

 Proposal Abstract - RFP-VI PI Scott Zengel