GROUNDWATER DISCHARGE AND ITS IMPACT ON SURFACE WATER QUALITY IN A CHESAPEAKE BAY INLET¹

Abstract

Surface water, groundwater, and groundwater discharge quality surveys were conducted in Cherrystone Inlet, on Virginia's Eastern Shore. Shallow groundwater below agricultural lields had nitrate concentrations significantly higher than inlet surface waters and shallow groundwater underlying forested land. This elevated nitrate groundwater discharged to adjacent surface waters. Nearshore discharge rates of water across the sedimentwater interface ranged from 0.02 to 3.69 litersm2•hr-1 during the surveys. The discharge was greatest nearshore at low tide periods, and decreased markedly with increasing distance offshore. Vertical hydraulic heads, Eh, and inorganic nitrogen flux in the sediments followed similar patterns. Nitrate was the predominant nitrogen species discharged nearshore adjacent to agricultural land use, changing to ammonium farther offshore. Sediment nitrogen fluxes were sufficient to cause observable impacts on surface water quality; nitrate concentrations were up to 20 times greater in areas of groundwater discharge than in the main stem inlet water. Based on DIN:DIP ratios, nitrogen contributions from direct groundwater discharge and tidal creek inputs appear to be of significant ecological importance. This groundwater discharge links land use activity and the quality of surface water, and therefore must be considered in selection of best management practices and water quality management strategies.

Effect of ultraviolet light on dissolved nitrogen transformations in coastal lagoon water

“…There is a gradient of organic matter and nutrient inputs across Hog Island Bay from the mainland to the islands, with the highest concentrations of dissolved N and sediment organic matter found closest to the mainland (McGlathery et al 2001). There are no riverine inputs to the lagoon, and the primary sources of allochthonous N to Hog Island Bay are seepage of nutrient-enriched groundwater (Reay et al 1992) and atmospheric deposition (Paerl et al 1990). Leaching of organic N from S. alterniflora biomass may be a source of N to the lagoon at times.…”

Submarine groundwater discharge: An important source of new inorganic nitrogen to coral reef ecosystems

“…Submarine groundwater flows into the coast at the interface between freshwater and seawater (the mixing zone) where the unconfined aquifer outcrops at the beach (Reay et al 1992). Toward the seaward edge of the mixing zone, water is brackish as a result of intrusion of salt water through permeable aquifer mixing as well as wave and tidal pumping (Li et al 1999).…”

Groundwater nutrient loading in Biscayne Bay, Biscayne National Park, Florida

“…Chesapeake Bay nutrient concentrations and discharge has been intensively studied and best management practices have been implemented (Reay et al 1992;Staver and Brinsfield 1996). Nitrate levels, in a main stem inlet, were up to 20 times greater due to groundwater discharge, which indicates groundwater is of significant ecological importance.…”

“…Nitrate levels, in a main stem inlet, were up to 20 times greater due to groundwater discharge, which indicates groundwater is of significant ecological importance. The management practices produced greater discharge by way of groundwater (Reay et al 1992). Staver and Brinsfield (1996) found annual nitrogen groundwater discharge to be 1.2 kg m-.…”

“…It was assumed most discharge would be found closer to the shoreline. Several researchers predict groundwater discharge decreases exponentially from shore (Lee 1977;Bokuniewicz 1980;Fellow and Bezonik 1980;Belanger et al 1985;Reay et al 1992;Robinson et al 1998). …”