Water Quality in the Delmarva Peninsula, Delaware, Maryland, and Virginia, 1999-2001

Abstract

What kind of water-quality information does the NAWQA Program provide? Water-quality assessments by a single program cannot possibly address all of the Nation's water-resources needs and issues. Therefore, it is necessary to define the context within which NAWQA information is most useful. • Total resource assessment-NAWQA assessments are long-term and interdisciplinary, and include information on water chemistry, hydrology, land use, stream habitat, and aquatic life. Assessments are not limited to a specific geographic area or water-resource problem at a specific time. Therefore, the findings describe the general health of the total water resource, as well as emerging water issues, thereby helping managers and decision makers to set priorities. • Source-water characterization-Assessments focus on the quality of the available, untreated resource and thereby complement (rather than duplicate) Federal, State, and local programs that monitor drinking water. Findings are compared to drinking-water standards and health advisories as a way to characterize the resource. • Compounds studied-Assessments focus on chemical compounds that have wellestablished methods of investigation. It is not financially or technically feasible to assess all the contaminants in our Nation's waters. In general, the NAWQA Program investigates those pesticides, nutrients, volatile organic compounds, and metals that have been or are currently used commonly in agricultural and urban areas across the Nation. A complete list of compounds studied is on the NAWQA Web site at water.usgs.gov/nawqa. • Detection relative to risk-Compounds are measured at very low concentrations, often 10 to 100 times lower than Federal or State standards and health advisories. Detection of compounds, therefore, does not necessarily translate to risks to human health or aquatic life. However, these analyses are useful for identifying and evaluating emerging issues, as well as for tracking contaminant levels over time. • Multiple scales-Assessments are guided by a nationally consistent study design and uniform methods of sampling and analysis. Findings thereby pertain not only to water quality of a particular stream or aquifer, but also contribute to the larger picture of how and why water quality varies regionally and nationally. This consistent, multiscale approach helps to determine if a water-quality issue is isolated or pervasive. It also allows direct comparisons of how human activities and natural processes affect water quality in the Nation's diverse environmental settings.

Travel time controls the magnitude of nitrate discharge in groundwater bypassing the riparian zone to a stream on Virginia's coastal plain

“…Overall, approximately 50% of Virginia's Eastern Shore is agricultural land, with 80% of agricultural area in row crops (USDA, 2002). Cropland is preferentially situated on well drained soils (Phillips et al , 1993) where NO 3 − fertilizers readily leach to generally aerobic groundwater (Denver et al , 2003). Commercial fertilizer (59%) and manure application (35%) to land make up nearly all the nitrogen load to catchments on the Delmarva (Brakebill and Preston, 1999).…”

“…Agriculturally derived nitrogen has leached to the unconfined Columbia aquifer (Denver, 1989) that supplies flow to the small coastal streams on the eastern shore of Virginia (Bachman et al , 1998). Nitrate concentrations in the Columbia aquifer often exceed the US EPA primary drinking water standard of 10 mg NO 3 − ‐N l −1 (Denver et al , 2003). The Columbia aquifer is composed of Pleistocene‐aged unconsolidated sands (generally 8–30 m thick; (Calver, 1968; Mixon et al , 1989)) with high hydraulic conductivity (5·53 × 10 −3 ± 1·56 × 10 −6 cm s −1 ; (Hubbard et al , 2001)).…”

“…In some cases, NO 3 − ‐rich water from adjacent agricultural fields may flow to the stream by paths that are too deep to allow interaction with riparian vegetation, a situation termed ‘riparian bypass’ (Jacks and Norrstrom, 2004; Wilcox et al , 2006; McCarty et al , 2008; Mills et al , 2008). Where NO 3 − bypasses biologically active riparian areas or where buffers do not exist, it may remain at high concentration as it moves through streambed sediments resulting in appreciable nutrient export to streams (Böhlke and Denver, 1995; Denver et al , 2003; Angier et al , 2005). In other cases, however, the streambed substantially reduces NO 3 − concentrations as the NO 3 − ‐rich water discharges to the stream (Lee and Hynes, 1978; Jacobs and Gilliam, 1985; Mills et al , 2008).…”

Wetland Restoration and Creation for Nitrogen Removal: Challenges to Developing a Watershed-Scale Approach in the Chesapeake Bay Coastal Plain

“…An extensive surficial aquifer overlies a series of confined aquifers. Image produced by the US Geological Survey, Hamilton et al (1991) with modification by Denver et al (2004). and elevated nitrate concentrations are found even near the base of the surficial aquifer (Hamilton et al, 1993;Debrewer et al, 2007).…”

Chesapeake Bay watershed pesticide use declines but toxicity increases

“…Pesticides do reach local water bodies through spray drift, storm water runoff, and groundwater transport. Pesticides have been found in streams in agricultural areas of the Delmarva Peninsula (the eastern shore of Chesapeake Bay, USA) during base-flow conditions when the water source is mainly groundwater seepage [2,3].…”