Upper Pocomoke River Basin: Determination of Transport Pathways and Estimation of Lag Time of Pollutant Delivery

WRD PROJECT #: MD167
PROJECT CHIEF: Donnelly, Colleen A.
BEGIN DATE: 01-July-1998
END DATE: 30-June-2001

Customers currently supporting the project:

Maryland Department of Natural Resources
U.S. Geological Survey

Problem

The Pocomoke River is one of three rivers in the Chesapeake Bay Watershed that was closed briefly during the Summer of 1997 due to reports of fish lesion outbreaks and massive fish kills thought to be associated with elevated levels of Pfiesteria piscicida or related toxic dinoflagellates found in the water at the time. Occurrences of Pfiesteria blooms and other toxic dinoflagellates are believed to be related to nutrient loading. Therefore, the State of Maryland is implementing legislation requiring farmers to adopt plans to control nitrogen runoff by July 2001 and phosphorous runoff by July 2004.

To provide the information and assessment tools required to estimate the contribution of all major nutrient sources, and to evaluate the effectiveness and timeframe of expected water-quality response of current nutrient-control efforts, a Watershed-Pollution Source Assessment is being conducted. The study involves characterization of pollutant sources through inspection and monitoring, estimation of pollutant loads through continuous monitoring and modeling, evaluation of management practices through paired watershed monitoring, and identification of pollutant transport pathways and associated nutrient traveltimes.

In the Pocomoke River Basin, elevated levels of nutrients in the soil run off into surface water and also travel through ground water and discharge to adjacent streams. Through the efforts of the U.S. Geological Survey (USGS) Ecosystem Program, the USGS has found that the percentage of total streamflow contributed by base flow in unconsolidated sediment of the Coastal Plain, where the Pocomoke River Basin is located, ranges from approximately 42 to 74 percent. Based on existing data, the nitrate concentrations in the surficial aquifers underlying the Pocomoke River Basin generally range from less than 0.1 to 35 milligrams per liter. The amount of nutrients delivered to the Bay and its tributaries from ground water may be significant and needs to be further quantified. Additionally, the apparent age of, and nutrient concentrations in, ground water throughout the Pocomoke watershed need to be defined to provide an estimate of how long nutrient-reduction practices may take to improve surface-water quality.

Objectives

Objectives of this project are to assist Maryland Department of Natural Resources (MDDNR) with relating hydrogeologic framework variability, ground-water transport pathways, and associated nutrient residence times. Secondary objectives include: identifying nutrient concentrations and residence times associated with sediments, and providing information to resource managers.

Approach

This is a 3-year cooperative project with the (DNR) and the USGS. A conceptualization of the hydrogeologic framework has been prepared and used to assess the characteristics that will influence chemistry and ages of water in the system. Ground-water sampling sites were established and samples were collected during the Summer of 1998 and analyzed for field parameters, major inorganic-ion and nutrient concentrations, nitrogen isotopes, and age-dating analyses using chlorofluorocarbons (CFCs) and isotope ratios of tritium/helium (3H/3He). Samples of sediment are being collected and analyzed for nutrient content in Federal Fiscal Year (FFY) 1999. In FFY99, core samples will be collected for analyses of age dates and geochemical tracers to estimate the age and residence times of nutrients and sediments in the basin. In FFY99, results of the ground- and surface-water analyses will be interpreted with knowledge of the hydrogeomorphic setting provided by the conceptual models to determine whether streams in different regions of the watershed are recharged by predominantly young or old ground water, the relations of the ground-water age to nutrient concentrations and sources, and the implications for surface-water response to management actions. Results will be documented in technical reports in FFY2000 and 2001.