USGS CMG 07005 Metadata

Electrical resistivity surveying,
submarine groundwater sampling with piezometers,
and groundwater discharge measurements in the
Corsica River Estuary

Samples and Chemical Analysis;Electrical
resistivity data, seepage meter data

The estuary of Maryland s Corsica River,
a small tributary on the eastern shore of
Chesapeake Bay, was the site of fieldwork during
April and May 2007. An interdisciplinary team of
U.S. Geological Survey (USGS) scientists
investigated submarine ground-water
discharge the movement of ground water into
the coastal ocean via underwater seepage.
Resource managers are concerned about nutrients
entering the estuary through this pathway,
leading to eutrophication, harmful algal blooms,
and fish kills. The Corsica River watershed has
been targeted by the State of Maryland for
implementation of intensive restoration efforts
to improve water quality.  The scientists sought
to test hypotheses about ground-water flow under
the estuary and ground-water discharge into the
estuary and to constrain the results of ongoing
modeling efforts by colleagues from the USGS
Water Resources Discipline, including Ward
Sanford. The team used a continuous
resistivity-profiling system (a method for
detecting low-salinity submarine ground water
over a large area), offshore piezometers
(temporary wells used to collect ground-water
samples from discrete depths), seepage meters
(devices for measuring direct ground-water
discharge at a particular location on the
sediment surface), and a raft equipped with
instrumentation to measure radon-222 (a natural
tracer of ground-water discharge). This work
expands on a previous investigation in the lower
Potomac River estuary in September 2006, which
characterized similar processes in that
geologically distinct and much larger,
western-shore tributary of Chesapeake Bay.
Results of sampling and geophysical measurements
indicate that the Corsica River estuary is
underlain by fresh ground water in sediment
pores at depths of less than 1 m to more than 5
m below the sediment surface, depending on
distance from shore and the presence of
confining units. In some locations, low-salinity
ground water may extend more than 200 m
offshore, as evidenced by electrical-resistivity
data. Brackish ground water that was more saline
than surface water was encountered at shallow
subsurface depths at sites more than 8 m from
shore, indicating submarine recharge during a
previous period when surface-water salinity was
higher. Samples of ground water and surface
water were collected for analysis of nutrients,
stable isotopes, radioisotopes, and age tracers,
among other parameters. Ground-water discharge
and submarine recharge at the site were highly
dynamic, as evidenced by changes in the salinity
of ground-water samples collected at the same
locations on different days, large variations in
seepage-meter measurements, and fluctuations by
a factor of three or more in surface-water radon
activities during the measurement period.  John
Bratton, John Crusius, and Kevin Kroeger of the
USGS Woods Hole Science Center (WHSC) in Woods
Hole, Massachusetts, conducted the work, with
assistance from other WHSC personnel, including
VeeAnn Cross, Chuck Worley, Laura Erban, Adrian
Green, and Sandy Baldwin. Collaborators included
Jennifer Bowen, who recently completed a term as
a Postdoctoral Scientist at the Woods Hole
Marine Biological Laboratory. Bowen performed
microbial sampling in the field and prepared
samples in the laboratory of Jeff Cornwell at
the University of Maryland Center for
Environmental Science Horn Point Laboratory. Bob
Shedlock (USGS Maryland-Delaware-District of
Columbia Water Science Center) provided helpful
input during the design stage of the field
effort.  The work was supported financially by
the USGS Coastal and Marine Geology Program
(John Haines, Program Coordinator), the USGS
Priority Ecosystems Science Program (Scott
Phillips, Chesapeake Bay Ecosystem Coordinator),
and the Maryland Department of Natural Resources
(John McCoy, Ecosystems Restoration Division
Chief). The field effort benefited significantly
from the logistical support and hospitality of
the Queen Anne s County Department of Parks and
Recreation (Gary Rzepecki, Parks Superintendent)
and the Corsica River Yacht Club (Reed Rogers,
Commodore).

Initial results presented at ERF meeting
in Providence, RI in 2007; USGS Chesapeake Bay
meeting Baltimore, MD, Dec 2007; and Ocean
Sciences meeting in Orlando, FL, 2008.
11 days at sea.
Related web site(s): http://soundwaves.usgs.gov/2007/08/

CMGP and PES, possible MD-DNR