From August 14 to 22, 2003, a team led by U.S. Geological Survey (USGS) scientists undertook a complex field effort to study the occurrence and chemistry of submarine ground water beneath Chincoteague Bay, MD, as a followup to earlier geophysical studies.
The area was made famous by Marguerite Henry's 1947 children's book (and later Disney movie) Misty of Chincoteague, about the wild horses that live on the adjacent barrier islands, Chincoteague and Assateague.
Chincoteague Bay is the site of nutrient over-enrichment that is of concern to its primary managers, the National Park Service and the Maryland Department of Natural Resources.
Submarine discharge of ground water recharged in agricultural areas on land is suspected to be a major contributor of nitrogen to the bay. Nitrogen and other nutrients are, in turn, suspected of fueling blooms of macroalgae that foul boat propellers and may be smothering seagrass beds, critical nurseries for young fish, shrimp, and crabs.
The recent field study used several techniques to gather data about the submarine ground water beneath Chincoteague Bay. Offshore work consisted of drilling, geophysical logging, and sampling performed from a barge platform, augmented by onshore logging of existing wells. The maximum drilling depth reached by the barge rig was 72 ft beneath the sediment surface.
The field team included chief scientist John Bratton and contract research assistants Sarah Kelsey and Dirk Koopmans (USGS, Geology Discipline, Woods Hole, MA); David Krantz and Abby Norton (University of Toledo, Ohio); John Earle (USGS, Water Resources Discipline, Denver, CO); and J.K. Böhlke and Craig Tobias (USGS, Water Resources Discipline, Reston, VA).
Drilling contractors from Hillis-Carnes Engineering Associates and a barge/tug pilot provided by Hi-Tide Marine Construction consistently overcame difficult mechanical, geologic, and meteorologic conditions to get the science done.
Special thanks go out to National Park Service colleagues from Assateague Island National Seashore, Brian Sturgis and Carl Zimmerman, who provided logistical support, shuttle boats, and lodging.
The fieldwork was conducted safely and efficiently and produced excellent scientific results.
Noteworthy discoveries included the presence of a plume of fully fresh ground water, more than 25 ft thick, extending more than 1/2 mi offshore along the west side of the bay (near Public Landing), a similar plume at the north end of the bay (near South Point), hypersaline brines underlying part of Assateague Island, and a widespread buried peat at the base of the bay's Holocene sediment.
Downhole gamma and electromagnetic-induction logs were obtained from eight locations.
Ground water was sampled from nine temporary subestuarine wells, surface water was sampled from eight locations, and pore water was squeezed from 35 sediment samples.
Additional analyses for age dating, nutrients, and stable isotopes will be performed over the coming months.
in this issue:
Water Beneath Chincoteague Bay, MD