Benthic nutrient fluxes in euphotic sediments along shallow sub-tropical estuaries, northern New South Wales, Australia

摘要: Diurnal benthic fluxes of dissolved inorganic and organic nitrogen (DIN DON) dinitrogen gas (N2) were measured in euphotic sediments 3 shallow sub-tropical Australian estuaries during 4 seasons. The included 2 impacted by sewage effluent (Brunswick Simpsons estuaries) 1 relatively pristine system (Sandon estuary). Sediments acted predomi- nantly as net sinks DIN throughout the year, except nutrient-enriched upper reaches Brunswick estuary, where large effluxes NH4 + occurred summer wet season. Distinct light/dark variations with reduced or reversal to uptakes light productive sediments. NO3 - was predominantly taken up at rates proportional ambient concentrations water column. DON commonly comprised a major fraction controlled primarily heterotrophic processes middle autotrophic lower estuaries. Large deficits amount remineralised (assuming breakdown 'Redfield' algae) indicated that significant is either denitrified immobilised biomass Benthic N2 suggest denitrifica- tion accounts for small missing immobilisation (and flow food chain) potentially pathway removal these Significant productivity also stimulated secondary production, promot- ing competition nutrient resources highest uptake coincided maximum metabolic diurnal p/r (gross productivity/respiration) between 0.5 1, suggesting peak this state. Denitrification lowest strongly related from column, may cause limitation Dissimilatory reduc- ammonium become more important column oxygen saturation drops below 40%, condition occurs regularly estuary. only effluxed (p/r 1). A conceptual model cycling proposed whereby favours expense denitrification recycling back