Original paper

Denitrification in the mainstem Neuse River and tributaries, USA

Whalen, S.C.; Alperin, M.J.; Nie, Y.; Fischer, E.N.


We conducted quarterly (spring, summer, fall and winter) determinations of denitrification at representative sites in the mainstem Neuse River and tributaries, USA. Denitrification measurements were made on intact sediment cores using the N2/Ar and isotope pairing techniques. We measured nitrate (NO3−-N) and ammonium (NH4+-N) concentrations in the water column at the time of core collection and evaluated rates of sediment-water exchange of dissolved oxygen (O2) in conjunction with denitrification rate determinations. Nitrate concentrations in the tributary streams and river water varied over an order or magnitude, from about 10 to 110 μmol/L, while NH4+-N concentrations were lower, varying from 0.6 to 10.8 μmol/L. Sediments consistently consumed dissolved O2, with rates varying from 256 to 1418 μmol m−2 h−1. Most cores actively denitrified with rates ranging to 222 μmol N2-N m−2 h−1. On average, coupled nitrification-denitrification accounted for 66 % of total denitrification. Lowest rates of denitrification were generally observed during December, when the water temperature was lowest at 4 °C. No other relationship was identified between rates of denitrification and measured physicochemical variables within or among sites or dates as sampling frequency and replication were low. Our study suggests that denitrification represents a sink of about 5 % for the NO3−-N load to the mainstem Neuse River and tributary streams.


stream sedimentisotope pairingcoupled nitrification-denitrificationoxygen consumption