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MEASURING BASE-FLOW CHEMISTRY AS AN INDICATOR OF REGIONAL GROUND-WATER QUALITY IN THE MID-ATLANTIC COASTAL PLAIN
Citation:
ATOR, S. W., J. M. DENVER, A. M. PITCHFORD, AND A. C. NEALE. MEASURING BASE-FLOW CHEMISTRY AS AN INDICATOR OF REGIONAL GROUND-WATER QUALITY IN THE MID-ATLANTIC COASTAL PLAIN. Presented at National Ground Water Association, 2005 Ground Water Summit, San Antonio, TX, April 17 - 20, 2005.
Impact/Purpose:
The overarching objective is to develop and test landscape indicator statistical models for condition of streams and aquatic biota in relation to pesticides, nutrients, sediments and toxic substances, nationwide. The indicator models will serve as tools for managers who want consistent methods to compare potential impacts on streams within a biophysical region for differing landscape patterns. To accomplish this objective, several sub objectives will be important:
Develop landscape indicator statistical models of stream vulnerability for selected regions of the U.S., beginning with the Mid-Atlantic Coastal Streams; studies in the Midwest, California, and the Southeast will follow.
Demonstrate the application of the landscape indicator models for the ranking of watersheds, the identification of "hot spots," and the evaluation of management options using projected future scenarios of land use for the study areas selected above.
Develop statistical distributions for physical characteristics of small water bodies for use in OPP modeling.
Leverage resources for this research by incorporating existing data into the model development process, and by sharing field study costs with other projects in the same geographic areas.
This task represents a topic area within the Landscape Sciences research program which is described in A National Assessment of Landscape Change and Impacts to Aquatic Resources. A 10-Year Research Strategy for the Landscape Sciences Program, EPA/600/R-00/001. It also supports the Regional Vulnerability Assessment (ReVA) Program.
Besides being responsive to the Office of Pesticide Programs, this research directly supports long-term goals established in ORD's multi-year research plans related to GPRA Goal 2 (Water Quality) and GPRA Goal 8.1.1 (Sound Science/Ecological Research). Relative to the GPRA Goal 2 multi-year plan, this research will "provide tools to assess and diagnose impairment in aquatic systems and the sources of associated stressors" and "provide the tools to restore and protect aquatic ecosystems and to forecast the ecological, economic, and human health outcomes of alternative solutions" (Long Term Research Goals 2 and 3). Relative to the Goal 8 multi-year plan, this research will develop and demonstrate methods to provide states, tribes, and federal, state and local managers with abilities to: (1) assess the condition of waterbodies in a scientifically-defensible and representative way, while allowing for aggregation and assessment of trends at multiple scales; (2) diagnose cause and forecast future condition in a scientifically defensible fashion to more effectively protect and restore valued ecosystems; and (3) assess current and future ecological conditions, probable causes of impairments, and management alternatives.
Description:
Water quality in headwater (first-order) streams of the Mid-Atlantic Coastal Plain during base flow in the winter and spring is related to land use, hydrogeology, and other natural and human influences. A random survey of water quality in 174 headwater streams in the Mid-Atlantic Coastal Plain (North Carolina through New Jersey) was conducted as part of cooperative research between the U.S. Environmental Protection Agency and the U.S. Geological Survey. Stream base flow was selected for sampling to represent an integration of shallow, primarily unconfined ground water from contributing watersheds. The unconfined surficial aquifer in the Coastal Plain provides water for domestic and public supply, and a significant portion of local stream flow. Nutrients and pesticide compounds have been detected i~ ground water in the aquifer in many areas over the past several decades.
Water samples were collected during base-flow conditions from late February through early June 2000. Base flow in headwater streams is typically dilute (median specific conductance, 90 micro siemens per centimeter at 25 dewees Celsius) and slightly acidic (median pH, 6); soluble minerals likely to significantly alter the chemistry of infiltrating precipitation along ground-water flowpaths are relatively uncommon in shallow sediments in most parts of the surficial aquifer. Concentrations ofnitrogen and selected herbicides in base flow similarly reflect their occurrence in unconfined ground water. Nitrate concentrations (as nitrogen) were as high as 12.4 milligrams per liter (mg/L), with a median of 0.42 mg/L. Metolachlor, atrazine, and selected metabolites of each are also detectable in most streams, although concentrations rarely exceed 1 microgram per liter. Empirical regression models were developed to demonstrate the effects of land use, soils, hydrogeology, and other influences on stream base-flow chemistry, and to predict the geographic variability of predicted water chemistry throughout the Mid-Atlantic Coastal Plain.