Modelling the diurnal variation of dissolved oxygen concentration in the River Oona

An investigation of the diurnal change of temperature and dissolved oxygen concentration from January to September 2002 in the River Oona, Northern Ireland, was completed. Continuous measurements were made using a YSI 6920 Sonde (15 minutes intervals) and the QUAL2E model was run in dynamic mode to simulate the diurnal variations of temperature and dissolved oxygen. Diurnal variation of dissolved oxygen was observed from March to September (88% to 125% saturation) with the lowest value occurring in early morning. The model accounted for the diurnal variation of temperature, but the maximum value was higher than that measured (1-2 "C). For dissolved oxygen, the simulation did capture the diurnal changes, although the peak value is predicted to occur 2-3 hours before the measured and the simulated maximum concentration was lower than that measured (0.5-2 mgll). Further modification of the model structure for dynamic dissolved oxygen simulation is necessary.