Abstract
Dissolved oxygen (DO) is a crucial indicator of water quality. DO usually shows a monotonic decrease along water depth during thermal stratification in reservoir, whereas metalimnetic oxygen minimum (MOM) is observed in some cases. Although MOM phenomena have been reported in different areas, the characteristics of different reservoirs are greatly different, and few comprehensive studies have been published regarding MOM in Chinese drinking water source reservoirs. The DO distribution along water depth was determined and the detailed reasons were clarified by two-years of field monitoring. In addition the effect of water lifting aerators (WLAs) on DO improvement was investigated in the Lijiahe Reservoir in Northwest China. A typical S-type DO distribution with two anaerobic water layers, below the epilimnion (10–25 m water depth) and above the sediment (bottom water), was observed derived from the decomposition of dead algae or organic matter and the restriction of DO vertical exchange. Moreover, after WLAs’ operation since 10 June 2018, the water body was completely mixed and DO was rich and uniform along water depth by eliminating the water stratification and inhibiting algae growth. The deep understanding of the DO distribution in a deep canyon-shaped reservoir and the technical support for reservoir restoration are meaningful for optimizing reservoir management.
Highlights
Reservoirs play an important role in supplying water for industry, agriculture, and residential drinking water [1,2]
The formation of metalimnion and its high density gradient has a profound effect on oxycline formation and dissolved oxygen (DO) depletion [4,5,6]
The objectives of the paper are: (1) to investigate DO distribution along water depth in Lijiahe Reservoir from 2017 to 2018, especially focus on DO depth profile during summer and autumn, to observe the formation of anoxia area below epilimnion; (2) to identify the key processes determining the formation of anoxia area below epilimnion; (3) to investigate the influence of water-lifting aerators (WLAs) on DO vertical profile, and confirm the WLAs’ capability to improve the water quality of reservoir
Summary
Reservoirs play an important role in supplying water for industry, agriculture, and residential drinking water [1,2]. S2 is located in the Improved water-lifting aerators were installed in theand main Lijiahe. The compressed air was situated in upstream of reservoir and 1.5 km from the S2 site. Delivered to WLAs through gas holder and air filters. The cooling system was designed to control the temperature of the operating system, including water pump, cooling pipe and return pipe. The compressed air was system had three distinguished functions: destratification, oxygenation and algae inhibition delivered to WLAs through gas holder and air filters. The gas flow of the WLAs system was controlled between 20 and 50 m /h, mainly temperature of the operating system, including cooling water pump, cooling pipe and return pipe
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