RAPID: Enhancing Biodegradation of Deepwater Horizon Contaminant Hydrocarbons in Louisiana Salt Marsh Using High Layer Charge Montmorillonites

Georgia State University Research Foundation, Inc., Atlanta GA

Investigators

Abstract

The purpose of this project is to immediately field-test the efficacy of clay mineral enhancement of both aerobic and anaerobic microbial degradation of petroleum hydrocarbons in coastal marshes impacted by the ongoing oil spill in the Gulf of Mexico. The project will test two specific hypotheses. First, that high-layer charge, high surface area phyllosilicates enhance aerobic biodegradation of petroleum hydrocarbons in coastal salt marsh settings. And second, that such enhancement can also be observed in anaerobic marsh environments. To test these hypotheses, three 25m2 experimental marsh plots will be seeded with a <0.5cm layer of montmorillonite clay, with adjacent unchanged control plots. Starting immediately, and proceeding over the course of one year, project personnel will sample these plots and monitor total petroleum hydrocarbon, hydrocarbon group composition, clay mineralogy and geochemistry, soil cation exchange capacity, aqueous major solute composition, heavy metals in fluid and solid phases, and microbial community composition. The subsurface environment will be simulated by an experimental microcosm using field samples of sediment and oil; anaerobic microcosms will be monitored in the same manner as the field sites, with the additional monitoring of functional molecular genetics of anaerobic sulfate-reducers known to oxidize petroleum hydrocarbons. The project will bring together a comprehensive suite of analytical techniques to acquire the needed data. The multidisciplinary research team assembled for this project has expertise in soils and clay mineralogy, molecular and environmental microbiology, analytical geochemistry, remote sensing, and geomorphology of Louisiana coastal salt marshes. Such crossdisciplinary collaboration is a powerful approach to the problem, and this will lay the groundwork for continued long-term research on the biogeochemistry of water-mineral-biota systems. The hypothesis-testing proposed for this project addresses several fundamental questions in water-mineral-biota interactions and environmental microbiology. First, for the first time it investigates in the field whether the charged microenvironment near the mineral-cell wall interface of petroleum hydrocarbon consumers enhances metabolic efficiency. This has been hypothesized based on previous laboratory studies, but the precise mechanisms are poorly known and the process has never been studied in the field. Second, this project addresses the critical question of the potential for anaerobic microbial communities to consume petroleum hydrocarbons. Although this has been doubted, recent evidence suggests that sulfate reducing microbial communities can play a significant role. If the clay mineral enhancement process observed in aerobic microbial communities functions similarly in anaerobic environments, it will shed light on fundamental aspects of the impact of sediment mineralogy on microbial ecosystem function. This investigation will lead to improved methods to enhance natural attenuation of contaminant petroleum hydrocarbons in salt marshes. In addition to responding to the current crisis in the Gulf, this will also help address the chronic worldwide problem of oil contamination in coastal marshes. The results of this investigation will be widely disseminated to the approximate 400 students per year enrolled in environment-related courses taught by the PI's at introductory and higher levels. Two PhD students (one Geosciences, one Biology) will contribute to the laboratory work for this project, and one female PhD student (Geosciences) will be directly supported. This will also provide three junior faculty with research experience related to an event of national significance.