Science Serving Maryland's Coasts

Katherine Martin, Bryn Mawr College

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Measuring Temporal Variability of Methyl Mercury and Methane in the Pore Waters of a Chesapeake Bay Tidal Marsh


This study assesses the use of OsmoSampler technology to monitor methylmercury (MeHg) production in a tidal marsh and examines temporal variability of MeHg in relation to controlling factors. We collected pore water samples in a Chesapeake Bay marsh using continuous pore-fluid sampling devices called OsmoSamplers. OsmoSampler technology has not previously been used in a coastal wetland or to investigate mercury cycling. We designed systems using OsmoSamplers to collect pore water samples for MeHg, methane, chloride, and sulfate analysis, sampling in a vegetated area and an area devegetated by clipping. Samples were collected over a 27 day period and stored in coils to create a temporal data set of in situ concentrations. This time series allows us to explore the methane-MeHg connection and the effects of vegetation removal on MeHg production. Some methanogens are known to methylate mercury, but the relative importance of the methane community in mercury methylation is not well understood. We hypothesized a positive correlation between methane and MeHg production, a decrease in MeHg production corresponding to vegetation removal, and that vegetation removal would inhibit sulfate reduction. We also sought to demonstrate the feasibility of using OsmoSamplers to look at MeHg flux in relation to these controls on mercury methylation. We conducted a lab experiment with a MeHg standard, comparative to the field experiment, to assess yield rate and resolution. This study is a preliminary exploration of OsmoSampler technology in a marsh environment. Using our system we have successfully collected samples from the vegetated area for methane, sulfate, and chloride analysis and collected and preserved samples from the devegetated area for MeHg and sulfate analysis. A number of issues arose when adapting the OsmoSampler technology to the collection of pore water in a terrestrial environment. We present the variability of measured concentrations with a discussion of adjustments for future long-term deployment.