Statistical analysis of estuarine profiles: III. Application to nitrate, nitrite and ammonium in the Tamar estuary

Abstract

Estuarine profiles of nitrate, nitrite and ammonium concentration taken over a period of six years were analysed by a statistical procedure. While nitrate profiles indicate conservative mixing, those of nitrite and ammonium exhibit maxima indicative of an estuarine input. Calculations using an advective analogue suggest that production of nitrite by oxidation throughout the water column would require unduly high populations of nitrifying bacteria (>10 6 cells l −1). Sedimentary production rates required to sustain the observed nitrite maxima are compatible with combined nitrification and denitrification rates observed elsewhere (1–2μmol m −2 d −1). The relative displacement of the nitrite and ammonium maxima and the frequent presence of a turbidity maximum in the Tamar estuary suggest that nitrite production in the sediment is probably augmented by water column nitrification in the region of the freshwater/brackish water interface. Simulations on the advective analogue provide circumstantial support for this suggestion.