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Published on Nov 2, 2016
We are researching the impact of seasonal variability on coastal mercury bioaccumulation by conducting bimonthly monitoring of mercury in phytoplankton, lagoon surface water and shallow groundwater at San Elijo Lagoon, as well as in nearshore seawater at the lagoon mouth. Coastal lagoons are ubiquitous along the California shoreline and provide essential habitat for a number of organisms, including many threatened and endangered species. Urban and agricultural development have resulted in a loss of coastal marine habitat which enhances the biological significance of these systems. Nutrient loading is a recognized threat to coastal lagoons; however little is known about mercury cycling in these ecosystems despite the connection between these two contaminants. Elevated nutrient concentrations promote large algal blooms, and the subsequent decomposition of algal biomass depletes oxygen in the water column, resulting in anoxia. This, in turn, supports anaerobic bacteria that convert inorganic mercury (HgII) into a more toxic bioavailable form, referred to as monomethylmercury (CH3Hg+ or MeHg). Since eutrophic conditions promote MeHg production, lagoons are an ideal environment in which to study nearshore MeHg production and biological uptake. It is generally accepted that physiochemical factors such as dissolved oxygen and temperature influence microbial respiration, and therefore MeHg production. However, seasonal drivers of phytoplankton-mercury interaction have not been investigated. Our project is designed to address three key questions: (1) Does the seasonal timing of a phytoplankton bloom affect MeHg uptake (i.e. stage of eutrophication)?; (2) Do smaller phytoplankton species take up MeHg more efficiently due to a higher surface area to volume ratio?; and (3) Does community structure influence phytoplankton-mercury interactions?