Study on carbon dioxide emission from reservoirs with different regulation types and its empirical prediction model

The construction of artificial reservoirs with various regulation types on river is currently an important form of comprehensive utilization of water energy and water resources in river basins. The type of regulation is important in controlling the residence time, which in turn affects the photosynthesis-respiration balance in the water. This process has a significant impact on carbon dioxide (CO₂) emissions from reservoirs. In this study, seasonal observations were carried out from September 2020 to July 2021 at five artificial reservoirs in the Qiantang River Basin, eastern China, to reveal the characteristics of CO₂ emission from the water-air interface of reservoirs with different regulating types. The results showed that the annual average CO₂ emission flux of the studied reservoirs varied significantly, ranging from 4.2 to 155.3 mmol m^-2 day^-1 with an average of 48.4 mmol m^-2 day^-1, which also had a significant negative correlation with the hydraulic retention time. While downstream of the dam, the annual average CO₂ emission flux was quite high with a range of 105.8 to 543.0 mmol m^-2 day^-1, averaging 381.6 mmol m^-2 day^-1. This is mainly due to the release of water with high-concentration CO₂ from the bottom of the reservoir. Additionally, using related data of reservoirs around the world, a CO₂ emission model with hydraulic retention time, air temperature, and reservoir age as the primary parameters was developed, which was conducive to evaluate reservoir CO₂ emissions on a larger scale and provided theoretical support for effective reservoir management.