A study was conducted between April 2004 and September 2005 to estimate groundwater and nutrient discharge to the Neuse River
estuary in North Carolina. The largest groundwater fluxes were observed to occur generally within 20 m of the shoreline. Groundwater
flux estimates based on seepage meter measurements ranged from 2.86 × 10
8 to 4.33 × 10
8 m
3 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 groundwater flux estimate (equal to about
9 m
3 s
−1), which assumed the narrowest groundwater discharge zone (20 m) of three zone widths selected for an area west of New Bern,
North Carolina, most closely agrees with groundwater flux estimates made using radon (3–9 m
3 s
−1) and Darcy’s Law (about 9 m
3 s
−1). A groundwater flux of 9 m
3 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 groundwater 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 groundwater discharge to the Neuse
River estuary is relatively minor, particularly compared with upstream sources of water and nutrients and with bottom sediment
sources of nutrients. Locally high groundwater discharges do occur, however, and could help explain the occurrence of localized
phytoplankton blooms, submerged aquatic vegetation, or fish kills.
Keywords Groundwater flux - Estuaries - Nutrients - Nitrogen - Phosphorus - Groundwater - Water budget - Seepage meter - Eutrophication - Nutrient loading