Factors at multiple spatial scales can influence photosynthesis in marsh habitats, from the species and conditions of individual plants, to the microsite variation in non-living and living resources, to the broader landscape-scale effects of tidal ranges, river inputs and oil spills. This project will study spatial patterns in photosynthesis of salt marsh plants which have been and will potentially be impacted by the BP Deepwater Horizon oil spill along the northern Gulf Coast. The investigators will test the hypothesis that salt marshes under higher stresses will be less resilient to oil spill disturbance. A stochastic modeling approach (Hierarchical Bayesian models) will be applied to address the research question. Its ability to quantify uncertainties and reduce uncertainties by assimilating new data makes it powerful approach.
The investigators will develop a scalable and transferrable methodology that can be used in river-dominated salt marsh ecosystems around the nation. It will advance the understanding of disturbance effects on ecosystem dynamics, and can be used to guide future research and management efforts in assessing long-term impacts and recovery of marshes impacted by oil spills. In addition, the project is expected to facilitate more informed wetland restoration plans at the impacted areas on the Gulf coast. This project will provide enriching and supportive educational experiences for two graduate students who will learn the basic techniques necessary to obtain and manage field based environmental data, and updated modeling techniques.
In this research, we studied oil contamination on Mississippi Gulf Coast due to 2010 BP oil spill and the impacts to photosynthesis of fringe marsh plant Spartina alterniflora to assess the resilience of coastal wetlands to oil contamination. We found: 1) Oiling was restricted to the fringing smooth cordgrass, and sediments within 10 meters of open water on Mississippi Gulf Coast; 2) ORO contamination decreased over time, as oil was transferred from plant detritus to the sediments, further weathering occurred, and some oil was lost with coastline erosion. 3) At Marsh Point in Davis Bayou, photosyntheis showed a rapid recovery after acute impact by oil contamination. Light reactions of photosynthesis measured by chlorophyll fluorescence using Mini_PAM recovered within 60-90 days. Recovery of the dark reactions, measured by CO2 flux using LI-6400, appeared to take somewhat longer, and reached rates comparable to control plants within 4-5 months. 4) Comparing the photosynthesis results from the plants at Marsh Point with those from Garden Pond in July 2011, we found that coastline energetics affect time to recovery. In low energy conditions (Garden Pond), oil remains trapped in the sediments and causes chronic depression of photosynthesis. In high energy conditions (Marsh Point), erosion of the shoreline promotes the removal of the oil residues and photosynthesis recovery. We have trained two graduate students, one post-doc, and two technicians during the study course on experimental design, data collection, data analysis, modeling and interpretation. We also developed a website to facilitate outreach and data access: https://sites.google.com/site/drcgrass/new-project/nsf-marsh-photosynthesis-and-oil-impacts
