Nitrification in the Scheldt Estuary (Belgium and the Netherlands)“

Nitrification and repartition of nitrifying bacteria were investigated in the autoepuration zone of the Scheldt estuary. Measurements of vertical profiles of nitrate and nitrite concentration in the interstitial water of sediments show that nitrification in sediments is very low, implying that most of the nitrate and nitrite production occurs in the water of the river itself. Nitrifying bacteria, probably of terresterial origin, are present throughout the water along a longitudinal profile of the estuary, with a regular decrease in numbers downstream. However, nitrification occurs only in a zone of favourable oxidation-reduction conditions, which coincides with the thermo dynamic stability fields of nitrate and nitrite with respect to ammonium