Microbiological and Physicochemical Aspects of Mercury Cycling in the Coastal/Estuarine Waters of Long Island Sound and Its River-Seawater Mixing ZonesEPA Grant Number: R827635
Title: Microbiological and Physicochemical Aspects of Mercury Cycling in the Coastal/Estuarine Waters of Long Island Sound and Its River-Seawater Mixing Zones
Investigators: Fitzgerald, William F. , Visscher, Pieter T.
Institution: University of Connecticut
EPA Project Officer: Hiscock, Michael
Project Period: October 1, 1999 through September 30, 2002
Project Amount: $592,035
RFA: Mercury: Transport and Fate through a Watershed (1999) RFA Text | Recipients Lists
Research Category: Water and Watersheds , Mercury , Water , Safer Chemicals
Description:The primary exposure of humans to methylHg (MMHg) is through the consumption of marine fish and fish products, yet the marine environment has been largely ignored and under sampled. Estuaries and adjacent coastal waters are major repositories for riverborne/watershed derived Hg species. Increased knowledge and understanding concerning the biogeochemical behavior and fate of Hg in important productive nearshore regions such as Long Island Sound (LIS) is a critical need. One of the most striking findings from our preliminary work is the presence of significantly large emissions of elemental Hg (Hg ) from the waters of LIS to the local/regional atmosphere. We postulate that Hg cycling in natural waters (i.e., LIS) plays a key or governing role in controlling the overall aquatic biogeochemistry of Hg and the bioavailable Hg species. We are proposing a three-year comprehensive physicochemical and microbiological marine program to investigate reactions and processes controlling Hg emissions, cycling, and bioavailability in Long Island Sound and its watershed/coastal water interface. Using prior Hg mass balance studies as a framework, we are proposing a experimental (large field and laboratory effort) and theoretical design (modeling) that will allow the results to be applicable to other regions of the coastal zone.
Objective: Our specific objectives are focused on several major features of the aquatic biogeochemistry of Hg and interactions between the terrestrial watersheds and nearshore marine waters. We will test the following hypotheses: (1) Hg distribution in LIS is spatially/ temporally variable, and related to the distribution of labile (bioavailable) Hg, the in-situ supply of reducing agents, bacterial activity and solar radiation. (2) In-situ organic matter production as reflected in differences between net primary production and bacterial consumption (i.e., activity) can serve as a surrogate for the amount of active organic substances that affect the biogeochemical fate of Hg in seawater (i.e., variations in Hg° production). (3) Estuarine reactions ( i.e., mixing of river borne Hg species with seawater high in Cl and major cations ) increase the labile Hg fraction available for reduction. We suggest that direct WTF discharges (sewage) into estuarine or coastal saline environments lead to an enhanced localized production of Hg° (e.g., East River; Boston Harbor).(4) Extensive and careful empirical documentation of the spatial and temporal variability of Hg in coastal waters such as LIS can yield: a) an indicator as to the status and trends of Hg in the system, and b) a means of assessing and constraining biogeochemical Hg cycling and mixing models. (5) Given the availability of reactive Hg species, and the limited light penetration in coastal waters, Hg is the predominant Hg cycling product of bacterial activity in the oxic zone. Net in-situ synthesis of MMHg is most significant in redox transition zones; the primary sites for this production in LIS are the shallower sedimentary regimes, and waters in basins that experience seasonal hypoxia (i.e., western and central LIS).