Nitrification in the Schelde estuary: methodological aspects and factors influencing its activity.

Abstract We present a 15-month dataset on nitrification measurements in the Schelde estuary (Belgium and The Netherlands). Nitrification was estimated using the N-serve sensitive dark (14)C-bicarbonate incorporation technique. A peak of nitrification activity was observed in the freshwater part of the estuary. Downstream from this peak, nitrification declined, probably because of ammonium limitation. A range of nitrification inhibitors was tested on both a Nitrosomonas europaea culture and estuarine samples. It was found that methyl fluoride and acetylene stimulated dark (14)C-bicarbonate incorporation and those inhibitors were therefore considered inappropriate nitrification inhibitors in combination with this technique. The effect of the inhibitor N-serve was studied on the dark incorporation of (13)C-bicarbonate into polar lipid derived fatty acids to further identify the dominant chemoautotrophic processes. Inhibition of polar lipid derived fatty acid labelling in the presence of N-serve was complete, suggesting that nitrifying bacteria dominated the chemoautotrophic community.