|Abstract Title:||NITROGEN STIMULATION OF MERCURY METHYLATION IN AN ESTUARINE LAGOON|
|Presenter Name:||Carl Lamborg|
|Company/Institution:||University of California, Santa Cruz|
|Session:||Mercury in Marine Ecosystems|
|Co-Authors:||Carl Lamborg,Jeanette Calvin,Xinyun Cui,Priya Ganguli|
Abstract Information :
Understanding the environmental conditions that support the production of methylmercury (MeHg) by sediment microbes is imperative, as MeHg biomagnifies in marine food webs and is the primary source of environmental mercury exposure for those who consume seafood. While anoxic or low-oxygen environments and sulfate-reducing bacteria have specifically been implicated in the production of MeHg, the relationship of nitrogen inputs to MeHg production has been found to be paradoxical. As nitrogen would be anticipated to increase the quantity of organic matter in a location, which would then provide a substrate for the metabolisms of microbes performing methylation, studies examining fertilizer inputs to salt marshes, lakes, and agricultural and non-agricultural wetlands, have instead provided results to the contrary. A further implication of these studies is that a decrease in nutrient loadings to coastal marine ecosystems could result in enhanced methylation. In the present study, seasonal observations of MeHg and various other predictors were collected in Younger Lagoon, Santa Cruz, CA (USA), a small seasonal lagoon bordered by agricultural land. In addition, methylation rate measurements using incubated sediment microcosms were conducted that included amendments designed to test for changes in methylation resulting from external loadings of nitrate and ammonium. Data were collected at two locations within the lagoon. The microcosms indicated that the sandier, lower organic carbon site responded to nitrate additions with an 7x increase in methylation rate but was unchanged after ammonium addition. No response to nitrate was observed at the muddier, higher organic carbon site. Stepwise multi-variable regression performed on the seasonal data from both sites suggests that NH4+ and Total N were statistically significant predictors of MeHg at the fine-grained, organic-rich site but that neither of these two parameters were significant at the sandy and low-organic site. We examine these paradoxical findings using additional parameters including sulfide and genomics.