Natural processes for managing nitrate in ground water discharged to Chesapeake Bay and other surface waters: More than forest buffers

Abstract

Nitrogen, phosphorus, and suspended sediment are contaminants that have widely contributed to the deterioration in the water quality of Chesapeake Bay and other surface waters throughout Virginia and the United States. These contaminants are derived from various sources and are transported to surface waters by surface (overland) runoff and ground-water discharge. Nitrogen and phosphorus stimulate growth of algae (eutrophication) and have been blamed, in part, for a decrease in the abundance of fish in Chesapeake Bay. Agricultural and residential application of fertilizers, land application of animal waste, discharge from septic tanks, and precipitation are major sources of nitrate (a common form of nitrogen) that leaches into ground water. As ground water flows through shallow aquifers and discharges to surface waters, it can contribute large amounts of nitrate to the surface waters. Forests adjacent to surface waters provide buffers that remove phosphorus and sediment from surface runoff. Numerous studies also have indicated that forest buffers remove much of the nitrate in ground water that flows beneath them from agricultural fields. A recent study (1991-93) on the Eastern Shore of Virginia (fig. 1), however, indicates that a variety of factors other than the presence of forest buffers actually control the amount of nitrate discharging from ground water to surface waters (Speiran, 1996). Knowledge of these factors is important to the management of nitrate in ground water that discharges to Chesapeake Bay and other surface waters. This report highlights major results of that study.