Estimation of groundwater and nutrient fluxes to the Neuse River estuary, North Carolina

Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Estuaries and Coasts 31 (2008): 501-520, doi:10.1007/s12237-008-9040-0.A study was conducted between April 2004 and September 2005 to estimate ground-water and nutrient discharge to the Neuse River estuary in North Carolina. Largest ground-water fluxes were observed to occur generally within 20 m of the shoreline. Ground-water flux estimates based on seepage-meter measurements ranged from 2.86 x 108 to 4.33 x 108 m3 annually and are comparable to estimates made using radon, a simple water-budget method, and estimates derived by using Darcy’s Law and previously published general aquifer characteristics of the area. The lower ground-water flux estimate (equal to about 9 m3 s–1), which assumed the narrowest ground-water discharge zone (20 m) of three zone widths selected for an area west of New Bern, North Carolina, most closely agrees with ground-water flux estimates made using radon (3–9 m3 s–1) and Darcy’s Law (about 9 m3 s–1). A ground-water flux of 9 m3 s–1 is about 40% of the surface-water flow to the Neuse River estuary between Streets Ferry and the mouth of the estuary and about 7% of the surface-water inflow from areas upstream. Estimates of annual nitrogen (333 tonnes) and phosphorus (66 tonnes) fluxes from ground water to the estuary, based on this analysis, are less than 6% of the nitrogen and phosphorus inputs derived from all sources (excluding oceanic inputs), and approximately 8% of the nitrogen and 17% of the phosphorus annual inputs from surface-water inflow to the Neuse River estuary assuming a mean annual precipitation of 1.27 m. We provide quantitative evidence, derived from three methods, that the contribution of water and nutrients from ground-water discharge to the NRE is relatively minor, particularly compared with upstream sources of water and nutrients and with bottom sediment sources of nutrients. Locally high ground-water discharges in the NRE do occur, however, and could help explain the occurrence of localized phytoplankton blooms, submerged aquatic vegetation, or fish kills.Funding support from the U.S. Geological Surve