The drought effect on water availability and quality of North Carolina water resources: Groundwater-surface water interaction and contributions of recycled wastewater


One of the critical questions in evaluating the availability of water resources in North Carolina is in determining how much water comes from different sources. These sources include (1) regenerating surface inflows from precipitation and local runoff; (2) base flows derived from groundwater discharge; and (3) base flow derived from anthropogenic (waste water and agricultural) recycled effluents. While most attention has been paid to evaluating the relationship between precipitation and runoff, this proposal seeks to evaluate the impact and contribution of the other two components (groundwater flow and recycled effluents). The current drought in the Southeastern USA has significantly reduced runoff derived directly from precipitation. If the drought continues, as some model predict, the relative contributions of groundwater discharge and man-made recycling water are expected to increase, affecting the quality of surface waters. However, current analytical tools for identifying and quantifying the relative contributions of these water sources are limited.

Here we propose a methodology to evaluate the impact of the projected drought on surface waters in NC. We propose to use several isotopic tracers coupled with geochemical analysis (major elements, trace metals and nutrients) that can provide information on the water sources and rate of discharge into the rivers of NC: (1) radium isotopes (226Ra, 228Ra, 224Ra, 223Ra) will be used to quantify the magnitude and rate of groundwater discharge into surface water; (2) strontium isotopes (87Sr/86Sr) will be used to elucidate the relative contribution of groundwater from small catchments with different geological terrains; and (3) boron isotopes will be used to identify and quantify waste waters contribution to surface waters. In addition, the study will investigate recycling of nutrients associated with effluent discharge and metals flux from the hyporheic zone, the area where water moves rapidly through sediments. Integration of available discharge information with the proposed multiple isotopic and geochemical investigation will enable us to quantify the relative contribution of the three principle water sources.

As part of the Center on Global Change (CGC) at Duke University we propose to conduct an initial survey that will include an investigation of a defined section of the Upper Neuss River and tributaries, up- and down-streams from Raleigh sewage treatment plant. In addition we will use the new research piesometers at the Duke Forest Hydrological Research Site to collect water samples from different depth intervals and relationship with New Hope Creek. The geochemical and isotopic evaluation generated in this project could be the base for a larger project that will attempt to evaluate the current drought conditions and to simulate different scenarios of the impact of the drought on water quantity and quality in North Carolina. Such a project could seek external funding from local (e.g., NC DENR) and federal agencies, such as the EPA Global Change Research Program (e.g., a joint EPA/National Center for Environmental Research call for proposals on “Consequences of Global Change for Water Quality”, or NSF programs that link Climate Change and Global Water Cycle (which is one of NSF 2008 Principal Areas of Focus).

Working group members:
Avner Vengosh, Nicholas School of the Environment
Robert B. Jackson, Department of Biology and Nicholas School of the Environment
Helen Hsu-Kim, Department of Civil and Environmental Engineering, Pratt School of Engineering
Emily S. Bernhardt, Department of Biology

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