Sediment-Water Nitrogen Exchange along the Potomac River Estuarine Salinity Gradient

ABSTRACT Cornwell, J.C.; Owens, M.S.; Boynton, W.R., and Harris, L.A., 2016. Sediment-water nitrogen exchange along the Potomac River estuarine salinity gradient. Observations of N2 efflux in estuarine sediments across the salinity gradient of the tidal Potomac River, a eutrophic subestuary of the Chesapeake Bay, were used to evaluate environmental controls of microbial denitrification. Rates of denitrification were measured using N2:Ar ratios in core incubations and were similar to other nitrogen-enriched estuaries, with summer and spring N2-N efflux rates averaging 54 ± 47 and 153 ± 97 μmol m−2 h−1, respectively. The paradigm of higher denitrification rates at lower salinities was not supported by observations during summer and spring conditions along this estuarine salinity gradient. Low bottom water oxygen concentrations in the lower, more saline part of the estuary resulted in low rates of coupled nitrification/denitrification. The most favorable region for denitrification in the tidal Potomac River ...