Mercury in Bays and Ponds of Cape Cod

Lamborg, Carl, Marine Chemistry and Geochemistry
William Martin, Marine Chemistry and Geochemistry

Project Funded 2007:

In recent work conducted in Waquoit Bay, we found highly elevated concentrations of dissolved total mercury (Hg). Simultaneous investigation of groundwater found similarly high levels which suggested submarine groundwater discharge as a significant source to that embayment. This was a new finding, which has garnered scientific attention (cover article in ES&T along with commentary/news release) and local concern (front page article in the Cape Cod Times, March 22 and 24 and a story on NPR). Our work comes on the heels of consumption advisories for fish in some Cape ponds (Ashumet and most recently, several ponds within the National Seashore boundaries). In all these cases, the primary source appears to be atmospheric deposition as it is in most locations in the U.S. The situation of Cape Cod may be unique in that our highly permeable and low organic carbon soils are poor at holding back and storing the Hg loaded onto our watersheds. The result appears to be that more Hg finds its way into our aquatic foodwebs than in locations with similar atmospheric loading.  

At the moment, however, this remains a hypothesis. A first important test is to begin to assess the scope of the problem by examining a number of water bodies on the Cape. This would include fresh and salt waters as both receive groundwater inputs. We will measure the amount of mercury and a bioaccumulating microbial metabolic byproduct form, monomethylmercury, in local pond and embayment waters, sediments and organisms. While doing this we will also measure the amount of dissolved radon (Rn). This will allow us to assess whether systems that receive a lot of groundwater (as indicated by Rn) also have high levels of Hg, and the chemical form of the Hg entering. Finally, we will explore the use of sediment cores and flux chambers for determining that amount of monomethylHg (the bioaccumulating form of Hg) that diffuses from bay sediments into the overlying water, and thereby begin to determine the relative importance of groundwater versus coastal production as a source of this form of Hg.