Characteristics of water quality response to hypolimnetic anoxia in Daheiting Reservoir

Abstract

Anoxia is a common phenomenon at the bottom of large reservoirs during thermal stratification. In an anoxic environment, an increasing amount of reducing substances and nutrients are released and settle at the hypolimnion of the reservoir, leading to water quality deterioration and eutrophication. This work presents a case study on Daheiting Reservoir, a part of the Water Diversion Project from the Luanhe River to Tianjin city. With the monitored data of the water temperature and dissolved oxygen content in the reservoir, and based on the mechanism of redox reactions, the water quality response to the hypolimnetic anoxia in Daheiting Reservoir was systematically analyzed. It was found that the release of total phosphorus from the sediments in Daheiting Reservoir was a joint effect of the biological and chemical processes, and the redox reaction in the anoxic zone boosted release of phosphorus. Anoxia in the reservoir caused the ammonia nitrogen released from sediments in the reservoir to accumulate at the hypolimnion, which increased the concentration of ammonia nitrogen in the water. Anoxia in the reservoir led to an increase in the concentration of iron and manganese, which accounts for the major driving factor of release of iron and manganese. HIGHLIGHTS This paper describes in detail the formation and development process of the hypoxic zone of the reservoir, and clarifies the temporal and spatial changes of the hypoxic zone of the reservoir.; This paper illustrates the accelerated release process of polluted sediments under hypoxic conditions, proves the relationship between hypoxia and deterioration of water quality.;

Keywords

• anoxic zone
• pollutant release
• thermal stratification
• water quality response