Collaborative Research: The effects of terrestrial organic matter inputs on coastal mercury cycling, methylmercury production and bioaccumulation

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Climate change will influence the delivery of contaminants, organic matter, and nutrients from land to the coastal ocean. This is because higher rainfall and warming increase runoff from land to coastal waters. Runoff also influences coastal algal blooms. These changes are expected to alter the distribution of mercury in the water and impact its availability for biological uptake. Mercury is a potent toxin. Its uptake into the food web contaminates fish and seafood and affects human health. This project will study how organic matter delivered from land to coastal waters affects mercury concentrations in seawater and in the food webs of the Gulf of Maine. The Gulf of Maine is one of the largest and most important coastal fishing grounds in the United States. This project will measure the concentration and isotopes of mercury on samples collected from research cruises under different algal bloom conditions and river flows. Lab experiments will be used to study how land-derived organic matter affects mercury accumulation in plankton. The project will provide research experiences for four undergraduate students in a STEM field. Training will be provided to a PhD student and a postdoctoral fellow. Findings from the project will provide critical information about the effect of climate change on mercury levels in marine waters and food webs. This information is needed for achieving the goals of the Minamata Convention, a global treaty for reducing mercury emissions to the environment.This project will examine the effects of climate change on terrestrial organic matter and mercury concentrations in Gulf of Maine waters. Specifically, the scientists will study the complex and often competing processes that influence: 1) mercury cycling and distribution; 2) the formation of methylmercury; and 3) methylmercury uptake to microplankton. Terrestrial organic matter plays an important role in transferring mercury from watersheds to coastal and offshore waters. It also controls the formation of methylmercury in water by providing a microenvironment that promotes the methylation of mercury by microbes, which represents the first step for uptake of methylmercury into seafood. However, some plankton can directly use organic matter as a food source (so-called “mixotrophs”) and can bioaccumulate methylmercury during feeding. Mixotrophs can dominate microplankton assemblages in coastal waters at some times of the year, and previous studies have not explored the impact of this feeding mode on methylmercury uptake at the base of the food web. This project will study the effects of organic matter dynamics on mercury and methylmercury cycling and bioaccumulation through 1) field surveys and shipboard experiments in the Gulf of Maine, where delivery of terrestrial organic matter is increasing, and 2) through laboratory microcosm experiments using autotrophic and mixotrophic microplankton taxa under contrasting carbon acquisition modes and organic matter characteristics and concentrations. This work will also apply novel mercury and methylmercury-specific isotope analyses and measures of organic matter quality to increase understanding of mercury cycling in coastal environments. This research will fill important gaps in predicting the effects of environmental changes on marine methylmercury levels, providing critical information to mitigating mercury emissions and methylmercury exposures, and for predicting changes in mercury levels in seafood in the future.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.