Collaborative Research: Halocarbon Biogeochemistry in Coastal Wetland Ecosystems - Exploring the Transition from Forested Wetland to Salt Marsh

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The relatively flat southeastern US coastal plain, from North Carolina to Texas, is particularly susceptible to sea level rise. As sea level rises, the boundary between the low-lying coastal freshwater forest and high marsh moves upslope. Highly productive forested wetlands are replaced successively by degraded wetlands and eventually by coastal salt marsh. Not only does saltwater intrusion change vegetation composition, high halide levels (called halogens) can interact with the large pool of soil organic matter through halogenation processes that are still poorly understood. These halogenation processes are important to elucidate as they produce volatile halocarbons that act as ozone-depleting compounds in the atmosphere. Halogenation of organic matter may also affect the decomposition rates of organic matter. This interdisciplinary research will improve our understanding of chlorine and bromine biogeochemistry and demonstrate the importance of halogens in carbon cycling. This collaborative research represents a new collaboration between four investigators with different specialties from universities in the northeast, southeast and western United States. Graduate and undergraduate students will have opportunities to interact with citizen scientists in an on-going EarthWatch project and learn how to disseminate the scientific knowledge to the general public. This study will also raise the awareness of the impacts of sea level rise on low-lying coastal areas in the Southeastern US.Halogens have historically been treated as inert elements in natural humification processes. However, numerous recent studies have demonstrated that chlorine and bromine are active components in C cycles. The overall goal of this research is to assess novel decomposition process routes of terrestrial organic matter in forested wetlands with high levels of chloride and bromide. The research project includes both field investigations and controlled experiments to determine the impacts of sea level rise on C and halogen biogeochemical cycles along salinity gradients in Winyah Bay, South Carolina. Fluxes of halogenated ozone depleting C compounds and greenhouse gases, as well as concentrations of organochlorine and organobromine in soil and litter and water will be quantified along salinity transects and within controlled plots. The research team contends that the novel method of determining X-ray absorption near edge structures (XANES) of halogenated organic matter in soil and detritus layers, coupled with measurements of halocarbon emission and composition in water using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS), will be useful in understanding the roles of halogens in C cycling. Determining the seasonal variation of halocarbon in air, soil, and water from freshwater forested wetland, salt-degraded wetland, and salt marsh sites, representing the transition of coastal wetland under sea level rise, will be useful in developing a mechanistic and landscape understanding of how sea level rise affects decomposition, humification, and halogenation processes of terrestrial organic matter in coastal wetlands. The controlled field experiments using different concentrations of chloride and bromide waters would illustrate their roles in humification and decomposition processes.