Benthic NHJ and NO5 flux following sedimentation of a spring phytoplankton bloom in Aarhus Bight, Denmark

Abstract

A seasonal study of NH4+ and NO3- fluxes and concentrations at the sediment-water interface was carried out at a 15 m deep station in Aarhus Bight, Denmark. In winter, NH4+ and NO3- were released from the sediment at comparable rates (0.20 to 0.40 mmol N m-2 d-1). A phytoplankton bloom ceveloped rapidly in early spring. Immediately after mass sedimentation of diatoms, the sediment transiently released NH4+ at a high rate (up to 1.5 mml N m-2 d-1) and a dramatic change to a NO3- uptake was observed (flux ca -0.80 mmol N m-2 d-1). Subsequently both the NH4+ release and NO3- uptake decreased (summer fluxes ca 0.35 and -0.15 mmol N m-2 d-1, respectively). From late summer, NO3- was again released from the sediment (ca 0.30 mmol N m-2 d-1) and a second, weaker maximum of NH4+ release (ca 0.70 mmol N m-2 d-1) was observed in fall. ...