Tidal fluxes of dissolved oxygen at the North Inlet-Winyah Bay National Estuarine Research Reserve

Advective, dispersive and total dissolved oxygen (DO) fluxes from 1297 complete tidal cycles were analyzed to test the “outwelling” hypothesis as it pertains to DO. A 910 day time series of meteorological and water quality data (approximately 35,000 half-hourly observations) was used to assess DO fluxes and dynamics at Crab Haul Creek, a small (1.1 km2) tidal salt marsh basin at North Inlet, South Carolina, within the North Inlet-Winyah Bay National Estuarine Research Reserve. A basin storage curve, derived from water velocity measurements made across a permanent transect in the tidal creek every half hour for eight semidiurnal tidal cycles, enabled water discharges to be estimated from tide height readings in the 910 day time series. The discharges along with DO concentration measurements were used to calculate DO fluxes for each tidal cycle in the series. The long-term mean dispersive and advective DO fluxes were −0.281 g O2 s−1 and −0.375 g O2 s−1, respectively. Based on “t” tests both means are significantly less than zero (p < 0.02), indicating exports. Furthermore a significant correlation was found between the dispersive DO export and the tidal mean solar radiation, indicating that photosynthesis is the principal process driving the dispersive export of DO. On the other hand no significant correlations were found between the advective export of DO and solar radiation or between the dispersive fluxes of DO and salt. The absence of such correlations indicates that the advective export of DO is simply an artifact of a slight ebb sampling bias in our computation of the tidal mean discharge. On a unit area basis the average annual dispersive export of DO is 8.9 g m−2 yr−1 or 0.28 mol DO m−2 yr−1. This is a small fraction of the oxygen produced in the basin by phytoplankton (18 mol DO m−2 yr−1) and its contribution to the DO resources of the receiving waters is far exceeded by the oxygen demand associated with the concurrent export of dissolved organic carbon (200–300 g m−2 yr−1).