Effect of Diurnal Variation of Dissolved Oxygen in a Eutrophic Polymictic Reservoir

Abstract

To evaluate the diurnal and seasonal Dissolved Oxygen (DO) variations and their effects on water quality, a comprehensive study was conducted in a eutrophic polymictic reservoir under artificially aerated and non-aerated conditions. The effect of aeration among sampling locations and along the water column of DO and DO saturation and diurnal variation of DO, water temperature, pH and conductivity was evaluated under aerated and non-aerated conditions. Dissolved oxygen and water temperature exhibited diurnal variations under aerated and non-aerated conditions; however, no notable diurnal variation was observed in conductivity and pH. The anoxic condition was observed in near-bottom waters at night under non-aerated conditions. The diurnal DO concentration at the surface level was higher under non-aerated conditions than aerated conditions. The diurnal DO variation implies that excessive algae and weed growth cause a major impact on DO production and consumption during the day and night, respectively. The DO concentration at different sampling locations revealed that artificial aeration increased DO concentration in the deep portion of the reservoir. However, results showed that the existing aeration system was inadequate to increase the DO concentration in the entire reservoir.