Characteristics of Sediment Oxygen Demand in a Drinking Water Reservoir

Abstract

Depletion of dissolved oxygen (DO) in the hypolimnetic layer during stratification periods and its deleterious effects on water quality have been widely observed. However, it is still difficult to comprehend conceptually the processes of oxygen consumption at the sediment-water interface. The research presented here is, therefore, based on an areal hypolimnetic oxygen demand (AHOD) model to address three key themes related to the sediment oxygen demand (SOD):① the characteristics of sediment and its influences on SOD; ② evaluation of SOD with different turbulence levels overlying the sediment; and ③ the influence of microbial metabolic activity on SOD. Sediment samples were collected at the entrance to and over the basin area of Jinpen Reservoir, and a sediment-water experimental chamber was designed to achieve these goals. The results showed that, under quiescent conditions, the SOD5area(SOD at DO of 5 mg·L-1) were 0.13 g·(m2·d)-1 and 0.36 g·(m2·d)-1 in the arm and basin, respectively. Under dynamic conditions, the slight mixing of the water column near the sediment induced an increase in SOD and resulted in a gradual shift from first-order to zero-order DO uptake. The organic matter content in the reservoir arm and profundal sediment were 44.43 mg·g-1 and 45.12 mg·g-1, respectively. The microbial metabolic activity in the basin was stronger, and the total fluorescence intensity of the dissolved organic matter (DOM) in the profundal sediments was about 1.5 times that in the reservoir arm. These results suggest that SOD will be higher when microbial metabolic activity is stronger and organic matter content is higher in sediments. The oxygenation aeration techniques should be designed to meet the oxygen demand of the deep reservoir to provide a theoretical basis for improving the oxygenation efficiency.