Influence of temperature and river discharge on water quality of the Western Scheldt estuary

Dissolved oxygen concentrations and information on the nitrification process collected respectively during a 14- and a 5-year period in the self-purifying part of the Western Scheldt estuary have been studied. In the polluted part of the stream, ammonium concentrations over the period 1967-1977 have been considered as well. This paper demonstrates the high variability of these three parameters (oxygen, start of the nitrification process, ammonium) owing to the hydrological conditions: temperature and river discharge. Neither the levels of ammonium in the polluted upper part of the stream, nor the concentrations of nitrate and dissolved oxygen in the recuperation part of the Scheldt estuary have been changed significantly during the periods studied (respectively 5, 10 and 14 years). A relation between these parameters and time could be hidden by hydrological factors. Water quality of a stream can be assessed by interpreting oxygen, nitrate and ammonium concentrations, only if all environmental and hydrodynamical parameters are known simultaneously