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Groundwater Discharge and Nitrate Loadings to the Coastal Bays of Maryland

By Jonathan J.A. Dillow and Earl A. Greene

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Nitrate in Groundwater discharged to the Atlantic coastal bays of Maryland enhances the growth of phytoplankton and algae in the bays, which in turn contributes to the process of eutrophication (changes in a body of water as nutrients and sediments accumulate), which is one of the principal environmental problems in the bays. Information on nitrate loading to the bays has been identified as a major data gap by State and Federal resource managers. This report presents results of a study to estimate Groundwater discharge and potential nitrate loads to the coastal bays of Maryland, which include Chincoteague, Newport, Sinepuxent, Isle of Wight, and Assawoman Bays.

The nitrate load from the discharge of Groundwater to the coastal bays is dependent on the concentration of nitrate in the water and the volume of Groundwater being discharged. Data from 388 wells completed in the surficial aquifer that discharges to the bays were used to construct a map of the distribution of nitrate concentration in the Groundwater. On the basis of those data, and on several simplifying assumptions, the potential nitrate load to the coastal bays from direct discharge of Groundwater was estimated to be 272,000 pounds per year, distributed throughout the 108-square-mile surface area of the bays.

Nitrate from Groundwater can also enter the coastal bays by way of base flow to streams that discharge to the bays. The potential nitrate load to the bays from the base flow of streams was estimated to be 862,000 pounds per year, assuming that the concentration of nitrate in stream base flow is 3.2 milligrams per liter, which is the median concentration of nitrate in Groundwater in the study area.

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