*The biogeochemical cycling of mercury in the coastal marine
environment*

Submitted by Michael Bothner

*Statement of the problem:* Mercury (Hg) contamination of freshwater and
marine fish has led to warnings in the United States and Canada to limit
fish consumption. Most of the mercury research by the USGS, however, has
been in freshwater environments. With respect to the marine environment,
major questions remain about the sources of Hg, its biogeochemical
cycling, and its fate. For example, recent research in Waquoit Bay on
Cape Cod has shown, for the first time, that ground water discharge from
the "subterranean estuary" is a major source of Hg to the bay (Bone et
al., ES&T, 2007).

*Objectives:* (1) Document the changes in Hg fluxes to coastal
environments in response to regulatory restriction of atmospheric
discharges in the U.S. and to increasing discharges of Hg by coal-fired
power plants in developing countries. (2) Explore the application of
stable Hg isotopes for identifying the sources of Hg found in coastal
sediments, coastal groundwater, and components of the coastal biosphere.
(3) Determine the historical record and present biogeochemical cycling
of Hg in methane-charged sediments off the mouth of the Penobscot River
in Maine before upstream sediments, known to be contaminated with Hg,
are transported to the bay after dam removal. (4) Explore the
application of enriched stable isotopes of Hg for tracing steps in the
biogeochemical cycling of Hg in laboratory experiments.

*Work strategy:* Conduct studies of Hg cycling in coastal environments
that have a wide range of salinity and of reducing and oxidizing
conditions in sediments. Sediments in stratified coastal basins overlain
by anoxic bottom water, and therefore not mixed by organisms, are ideal
for establishing a historical record of contaminant accumulation.
Analysis of rates of Hg cycling in a range of geochemical environments
allows extrapolation of results to other areas. Potential study sites in
the Northeastern U.S. also include migration routes of anadromous fish
and piscivorous birds (e.g. alewives, osprey), permitting investigation
of the transport pathways between Hg in sediments, water, and the
coastal biosphere.

This project description addresses two of the science directions
proposed in the new Science Strategy of the USGS: "Understanding
Ecosystems and Predicting Ecosystem Change", and "The Role of the
Environment and Wildlife in Human Health."

*Relevance and impact:* This research addresses fundamental questions
about the response of the environment to changes in the local and global
discharge of Hg to the environment. The research results will provide a
means of testing the effectiveness of regulations that limit discharge
or impose mitigation. Knowledge of the sources, sinks, and pathways for
Hg in coastal systems also provides input to policy decisions that
protect human and environmental health.

*Partnerships:* Partnerships are already established between Coastal and
Marine Geology, scientists in WRD, the Woods Hole Oceanographic
Institution, Massachusetts Department of Environmental Protection, and
the Penobscot River Restoration Project. New partnerships will be made
with other USGS Hg programs and other state and federal agencies.