Ground water beneath coastal bays of the Delmarva Peninsula: Ages and nutrients

Groundwater
By: , and 

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Abstract

To complement a large-scale geophysical investigation of occurrence and discharge of fresh water beneath Delaware, Maryland, and Virginia (Delmarva) coastal bays, we measured (1) salinity and nutrient concentrations in ground water samples from several offshore coring sites and (2) a suite of chemical and isotopic parameters, including age tracers, in ground water samples from a Delaware site. Samples were collected in a variety of Holocene and Plio-Pleistocene sediments in nearshore and offshore areas of the bays. Ground waters that were significantly fresher than overlying waters were found in plumes up to at least 15 m thick extending to more than 500 m offshore in some areas. Steep salinity and nutrient gradients occur within a few meters of the sediment surface in most locations studied. The zone of transition from deeper fresher waters to shallower brackish waters is generally thin near shore, but thickens and becomes more gradual offshore. Ground water ages at the Delaware site were mostly < 50 yr in both fresh waters and brackish waters up to 22 m below the bay bottom. Water chemistry and age data indicate that fresh water plumes beneath the estuary are active extensions of the surficial aquifer carrying nitrate from recharge areas on land, whereas brackish ground water surrounding the fresh water plumes is recharged beneath the estuary and contains ammonium and phosphate released by diagenesis of shallow estuarine sediments. Denitrification affects some of the fresh water nitrate before it mixes with brackish ground water or discharges to surface water.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Ground water beneath coastal bays of the Delmarva Peninsula: Ages and nutrients
Series title Groundwater
DOI 10.1111/j.1745-6584.2004.tb02641.x
Volume 42
Issue 7
Year Published 2004
Language English
Publisher Wiley
Contributing office(s) Toxic Substances Hydrology Program, Woods Hole Coastal and Marine Science Center
Description 14 p.
First page 1021
Last page 1034
Country United States
State Delaware, Maryland, Virginia
Other Geospatial Delmarva coastal bays
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