Carbon dioxide emissions from the Geheyan Reservoir over the Qingjiang River Basin, China

Abstract In recent years, researchers have given an increasing amount of attention to carbon matter interception and greenhouse gas emissions from large hydropower reservoirs. The Geheyan Reservoir was selected as a typical canyon case to carry out continuous measurements of greenhouse gas fluxes from March 2015 to February 2016. Carbon dioxide (CO 2 ) fluxes from the interface between the water and atmosphere were identified at the following sites: above the dam, upstream, in a tributary, in the drawdown area, and in a bay within the reservoir. Results indicated that average CO 2 fluxes in Geheyan Reservoir were 55.69 + 66.33 mg m −2  h −1 . Carbon dioxide emissions were lower in spring and summer when the water level frequently varied for flood control. In addition, CO 2 fluxes were higher when water flowed slowly with relatively high water levels that remained stable continuously. On a spatial scale, CO 2 emissions were lower in the drawdown area of the tributary and below the dam, while higher CO 2 emissions occurred in the typical bay area where water velocity was very slow. Therefore, it can be concluded that a longer residence time and slower water velocity caused generally higher CO 2 emissions from Geheyan Reservoir. The seasonal change of CO 2 fluxes in the Yuxiakou backwater-area monitoring point was very stable no matter how the water level changed, but was higher than below the dam and in the drawdown area in most months. Temporal and spatial patterns of CO 2 fluxes were significantly controlled by water temperature among all environmental variables for Geheyan Reservoir.