Total Sediment Mercury Above and Below the Mill Pond Dam in Durham, New Hampshire
Abstract
Mercury is a pervasive environmental contaminant, and it has multiple pathways into ecosystems and watersheds. The primary pathway of mercury distribution is through the atmosphere, where gaseous mercury remains aloft for up to a year and can be transported long distances. A secondary pathway of mercury distribution is through point sources, which are identifiable sources of pollution or contaminants. Once mercury is introduced into landscapes, it has the potential to migrate into other environments, where it can enter marine and freshwater aquatic ecosystems.
It is important to study mercury because specific types of mercury are indicators of environmental health. This health is not directly linked to atmospheric mercury concentrations or even to total amounts of mercury, but production of the bioaccumulative methylmercury is a chief source of environmental concern (Driscoll et al., 2013). Methylmercury targets the central nervous system, and its toxicity as a neurotoxin has been known since the 1950s (Castoldi et al., 2003). Studies show that mercury can transform into methylmercury under certain environmental conditions, so studying mercury contents in the environment helps to identify potential places of concern.
The Mill Pond Dam, a head-of-tide dam in Durham, New Hampshire, separates tidal waters from fresh water in the Oyster River. Though the Town of Durham voted to remove the dam in March 2022, the dam is still in place as of March 2024 and remains scheduled for removal in the forthcoming years (Dandurant, 2022; New Hampshire Department of Environmental Services, n.d.). Below the Mill Pond Dam lies the Great Bay Estuary environment, which is an area where fresh water from the Oyster River mixes with salt water that drains out to the Atlantic Ocean. Freshwater environments above the dam include the Mill Pond, College Brook, and the Oyster River.
Prior research has identified areas with elevated levels of total mercury in cored sediments in Mill Pond (Miller, 2020). This project seeks to investigate these findings in greater detail by evaluating how mercury concentrations, together with organic matter, vary above and below the Mill Pond Dam. This project was conducted in 2023 with a Summer Undergraduate Research Fellowship (SURF) from the Hamel Center for Undergraduate Research at the University of New Hampshire.