| Summary |
AGU Fall Meeting 2004 abstract H24A-04. Title: Use of Continuous Resistivity Profiling to Detect Low-Salinity Ground Water Beneath the Upper Neuse River Estuary, North Carolina. AUTHORS: Bratton, J F, USGS, 384 Woods Hole Rd., Woods Hole, MA 02543, United States; Crusius, J F, USGS, 384 Woods Hole Rd., Woods Hole, MA 02543, United States; Meunier, J K, ENSCO/USGS, 12201 Sunrise Valley Dr., Reston, VA 20192, United States; Spruill, T B, USGS, 3916 Sunset Ridge Rd., Raleigh, NC 27607, United States; Wrege, B M, USGS, 3916 Sunset Ridge Rd., Raleigh, NC 27607, United States. ABSTRACT: The Neuse River Estuary (NC) has recently experienced fish kills associated with low dissolved oxygen events and blooms of toxic dinoflagellates, along with other problems linked to eutrophication. As part of a larger project to constrain nutrient budgets, a field investigation was initiated in April 2004 to study occurrence and discharge of fresh and brackish ground water and nutrients beneath the estuary itself. A continuous resistivity profiling (CRP) system was used to map the depth of the freshwater-saltwater interface (FSI) in sub-estuarine ground water. A total of 154 km of lines surveyed yielded 108 km of high-quality data after processing. Typical depth penetration of the CRP system was 20 to 27 m below the sediment surface. Patterns observed in the data included downstream and offshore deepening of the FSI in sub-estuarine ground water, as well as offshore plumes of low-salinity water beneath shoals and in buried paleochannels. In transects near the head of the NW-SE trending upper estuary, the resistivity-defined FSI (>25 ohm-m) was 11-18 m below the sediment surface. Shore-parallel tracks collected less than 800 m from shore in < 3 m of water indicated that the FSI along the northeast shore and most of the southwest shore of the estuary was >10 m below the sediment surface, with isolated zones where the FSI was at or near the sediment surface, and longer stretches with the FSI >24 m deep. An exception to this was an area of apparent discharge along approximately 6 km of 9-m-high bluffs in the Riverdale area of the southwestern shore. Offshore data collected parallel to the estuary axis between Cherry Point and Thurman showed no significant low-salinity ground water in the eastern half of the upper estuary, except for a few plumes extending offshore from the south shore. One of these plumes originated at a discharge area adjacent to Cherry Point Marine Corps Air Station and extended at least halfway across the estuary, with the depth of the FSI increasing with distance from shore. Available seismic data indicate that the plume may lie in a buried paleochannel. Elevated surface water concentrations of radon are also consistent with discharge in this area. A second plume was observed extending beneath a shoal offshore from Cherry Point, with the FSI at a depth of about 8 m out to the edge of the shoal. |
| Comments |
Resistivity profiles available at: http://nc.water.usgs.gov/ccp/2004Crystal/data/resistivity/frameindex.html. Project web page: http://nc.water.usgs.gov/ccp/2004Crystal/data/resistivity/frameindex.html. Original Center People field contained: John Bratton, scientist; John Crusius, scientist; Dirk Koopmans, contract technician; Emile Bergeron, marine technician.
Project = Atlantic Coastal Ground Water: Neuse River Estuary, Atlantic Coastal Ground Water: Neuse River Estuary |
