Effects of Seasonal Thermal Stratification on Ammonia Nitrogen Transformation in a Source Water Reservoir

Abstract

Seasonal thermal stratification has a significant impact on water quality. In this paper, the variation of vertical distribution of ammonia nitrogen in a source water reservoir was studied, on the base of field monitoring data. The dominant factor of the variation in ammonia nitrogen is the anaerobic environment caused by the seasonal thermal stratification, which leads to the degradation of nitrogen-containing organic compounds in the sediments. To determine the rates of ammonia accumulation, an in situ experimental chamber was used. The results showed that, before the formation of thermal stratification in the reservoir, sediments in the bottom of the water have a high tendency to release ammonia; the rates of ammonia accumulation in the overlying water are 40.31–111.41 mg·m−2·d−1. However, thermal stratification causes changes in the physical and chemical properties of the sediment and reduction in the degradability of the nitrogen-containing compound in the sediment. The rates of ammonia accumulation (39.44–44.65 mg·m−2·d−1) after thermal stratification are lower than before. Considering the water pollution hazards caused by seasonal thermal stratification, it is necessary to take corresponding emergency response measures to cope with the possibility of water pollution risk.

The fate of anthropogenic nitrogen in a redox stratified pond: an isotopic approach

“…This internal recycling may comprise the primary mechanism for the high levels of N retention in the pond's deepest layers, where total dissolved N reaches to 775 uM. Similar ammonium accumulation trends have been noted in other highly stratified systems (Beutel, 2001;Cutrofello and Durant, 2007;Shi et al, 2021). Considering NH 4 + assimilation by phytoplankton as a secondary sink of NH4 + from the middle layer, the variations in the requisite 15 e of NH 4 + loss may actually reflect variations in the relative magnitudes of these processes.…”

Seasonal Variation and Vertical Distribution of Inorganic Nutrients in a Small Artificial Lake, Lake Bulan, in Mongolia

“…The concentration of NH + 4 −N in bottom water increased over time during summer and winter stratification owing to decomposition of organic matter [21,52,53]. The low DO concentration at a depth of 7 m in August (Figure 4c) can be explained as similar to the thermal classification and summer stratification [10]. Jaeger [54] reported that the lowest DO concentrations were observed during summer in the hypolimnion (6-10 m depth) and surface sediments of a small urban lake, Lake Krupunder in Germany.…”

“…Small lakes at temperate latitudes provide important indicators of the impacts of anthropogenic activity and global warming on water quality, which include the duration of thermal stratification in summer and lake mixing regime [9,10]. Stable stratification prevents the exchange of water between the surface and bottom layers and has a significant impact on the physical and chemical parameters of the water quality [10].…”

“…Small lakes at temperate latitudes provide important indicators of the impacts of anthropogenic activity and global warming on water quality, which include the duration of thermal stratification in summer and lake mixing regime [9,10]. Stable stratification prevents the exchange of water between the surface and bottom layers and has a significant impact on the physical and chemical parameters of the water quality [10]. Thermal stratification obstructs the reaeration pathway to the bottom layer, and when dissolved oxygen (DO) in the water is consumed during organic matter decomposition, it results in the formation of an anaerobic environment in this layer [11,12].…”