Magnitude of Ground-Water Inflow and Nutrient Loadings to the Coastal Bay Watersheds of Maryland

WRD PROJECT #: MD128
PROJECT CHIEF: Dillow, Jonathan J.A.
BEGIN DATE: 01-April-1998
END DATE: 30-September-1998

Customers currently supporting the project:

U.S. Environmental Protection Agency

Problem

Eutrophication caused by excessive nutrients in estuaries is one of the most important environmental problems in the Maryland Coastal Bays. The magnitude of nutrient loads from ground water has been identified as a major data gap that warrants immediate attention. Knowledge of the relative importance of ground-water sources of nutrients in relation to other point and nonpoint sources, as well as the spatial distribution of different degrees of nutrient loading from ground water, is needed to target areas for monitoring and for nutrient management.

Objectives

Develop a reasonable estimate of ground-water flux and nutrient loading to estuaries within Maryland's Coastal Bays.

Approach

An estimate of ground-water flux and nutrient loads will be developed. The following are the major tasks needed to fulfill the study objectives.

1. Compile existing geologic and hydrologic data from maps, driller's logs, and previous regional and local hydrologic studies.
2. Characterize the hydrogeology of the Coastal Bays' watersheds and determine the ground-water-flow system boundaries. Construct cross sections from upland watershed boundaries through the estuary in several locations to illustrate local ground-water-flow systems. This activity will focus on the surficial aquifer, which is the source of most ground-water-derived nutrients for the estuary.
3. Calculate the flux of ground water entering the Coastal Bays from the surficial aquifer. This will be accomplished using standard hydrologic analytical (flow-net) techniques for each segment of the watersheds.
4. Estimate concentrations of nitrate and phosphorus in ground water. Existing water-quality data from local wells will be used, if available, along with estimates based on concentrations commonly seen in areas of similar soils, land-use patterns, and flow paths.
5. Calculate the potential loading of nutrients from ground water by combining estimates of nutrient concentrations in ground water with the flux estimates. This analysis will include consideration of the potential for denitrification in ground water, or at the ground-water/surface-water interface to the degree possible with available data reports.