The release of an estimated 4.9 million barrels of oil from the Deepwater Horizon (DWH) event exposed the nation's largest and most productive wetland-estuarine environment to an unprecedented potential for environmental damage. The Mississippi River delta coastal wetland system, which comprises almost 40% of all coastal wetlands of the 48 conterminous United States, is of special concern not only to the northern Gulf of Mexico, but also to the nation because of the suite of environmentally and economically important services it provides, which include hurricane and storm protection, water quality enhancement, faunal support, sedimentation and carbon sequestration, and many others. Most, if not all, of these ecosystem services are dependent on a healthy, functioning plant-microbial-benthic system. The impacts of the oil spill on coastal marshes and the plant-microbial-benthic system have, and continue to be, documented. Our own findings quantify severe impacts to flora and fauna, in particular where oiling levels are high. Much less well understood, however, is the extent to which the plant-microbial-benthic system has recovered, and how specific remediation actions, such as physical spill response treatments, vegetation plantings, and fertilization, might accelerate the rate of recovery. Thus, the overall goals of the proposed research are to (1) document longer-term impacts of the DWH event on the plant-microbialbenthic system, (2) quantify rates of, and controls on, plant-microbial-benthic recovery, and (3) evaluate the effectiveness of remediation treatments for accelerating rates of recovery and long-term sustainability of the plant-microbial-benthic system. The proposed research supports the GoMRI’s theme 3: (1) knowledge of environmental effects of petroleum on wetlands, marshes and organisms and (2) the science of ecosystem recovery and means for accelerating recovery.
In general, oil spills can cause widespread impacts to the structure, function, resilience and sustainability of coastal wetlands depending upon oil type, volume, degree of weathering, mode of contact and other environmental and biotic factors. Our ongoing GRI-LSU funded research has demonstrated impacts of the Macondo oil to coastal wetlands. In moderately oiled marshes, speciesspecific differences in oil sensitivity were apparent, modifying vegetation structure from a Juncus roemerianus-Spartina alterniflora community to mostly Spartina. These impacts may influence the ecology and trophic linkages of the affected marshes. Heavy oiling, in contrast, almost completely killed marsh plants, reduced some benthic fauna, and decreased overall bacterial populations. Many bare, unvegetated marsh shorelines remain, with little evidence of recovery more than one year post-oiling. Along these heavily oiled shorelines, ecological structure and function have been greatly modified in the absence of recolonizing vegetation, and marsh recovery and sustainability may be seriously jeopardized. One approach for promoting the ecological restoration of severely oiled marshes is by the transplantation of native vegetation to accelerate recovery of ecological structure and resulting function. This remediation strategy, in combination with nutrient stimulation and prior physical response treatments, will be evaluated in the proposed research.
Collectively, our research experience on oil impacts and remediation, in general, and the DWH spill, in particular, make our research team highly qualified to conduct the proposed research - we have published more than 50 refereed scientific papers on oil spill science; with one published paper [Lin and Mendelssohn 2012] and another presently in press [Mendelssohn et al. 2012] on the DWH spill). Our current study sites will be used to investigate the effects of various oiling scenarios on long-term impact, natural recovery and sustainability of the plant-soil-microbial-benthic ecosystem. Our extensive database on impact and initial recovery to date will provide the essential baseline information from which to assess recovery. In addition, we will use these existing marsh remediation treatment test sites, established by the DWH spill response, to evaluate the effects, and effectiveness, of various remediation strategies, in combination with vegetation plantings and fertilization, on recovery, resilience, and long-term sustainability of the DWH oil-impacted marshes. The proposed research will emphasize ecological assessments of plant structure and function, marsh integrity, cultivation-based and modern molecular biological analysis of microbial communities, stable isotope signatures of dominant benthic communities and faunal abundances, and soil biogeochemical techniques. This proposed research will provide a better scientific understanding of the effects of disturbance on the impact and recovery of the plant-microbialbenthic ecosystem as well as practical information concerning strategies for accelerating ecosystem recovery, and thus long-term sustainability, of oil impacted coastal wetlands.