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The Response of Mercury Species and Related Genes to Long‐term Fertilization in a New England Salt Marsh

Abstract

Mercury (Hg) is a toxic trace metal which has an insidious tendency to bioaccumulate in marine foodwebs.  Furthermore, human activity has significantly increased the amount of Hg moving in the environment, which may ultimately impact the health of fisheries and coastal ecosystems.  A great deal of research effort has been expended on studying the scope of direct human emissions, but as we are now learning, there can be consequences for the cycling of Hg in the environment from other human impacts.  One of these that we are now examining is the impact that nutrient loadings on the coastal zone (for example from septic systems) can have on the accumulation of Hg in marine foodwebs.  We and others hypothesize that increased nutrient loadings may actually decrease the amount of monomethyl Hg (CH3Hg+) produced by coastal ecosystems and that, paradoxically, as we seek to clean up coastlines by decreasing nutrient inputs we may induce higher concentrations of Hg in fish.

This hypothesis has yet to be tested, but a local research site in the Great Sippewissett Marsh (GSM) offers the ideal platform on which to conduct this experiment.  In certain parts of GSM, colleagues have been fertilizing the salt marsh for several decades in an effort to understand how nutrients like nitrogen are retained and modified as overall loads are increased.  Thus, the GSM fertilization plots will allow us to easily sample stretches of marsh that have experienced a range in chronic nutrient load, and test whether this deliberate perturbation has affected the Hg cycle in this marsh.  Furthermore, some work has already been done regarding Hg in this marsh (early in the fertilization history) and therefore will allow us to examine the effect of chronic perturbation on the system through new studies.  We propose to collect sediment and porewater samples for the analysis of Hg, CH3Hg+ and a suite of relevant other chemical and biological parameters (e.g., organic carbon, sulfur, DNA) to place any changes in the Hg cycle of the different plots in context.  Questions to be raised and answered include whether or not changes in the carbon and sulfur cycles (typically very influential on Hg) can be used to predict the Hg changes and whether changes in the microbial communities of the plots can also offer insight on Hg dynamics.  This last component, the effect of microbes, will be vastly aided by the recent discovery of two specific genes present in some anaerobic bacteria that are responsible for the transformation of Hg into CH3Hg+.  We will hunt for these genes, and others, in the fertilization plots which will represent a first ever application of this kind of genomic‐aided Hg research in the field.  For this reason, the proposed work will be transformational for Hg research in general and for our laboratories, as this project will provide for us the time and resources to “spin‐up” the ability to measure new Hg‐cycling genes in environmental samples and provide the basis for larger proposals in the future.

Last updated: August 5, 2013