The Partial Pressure And Flux Of CO₂in The Xinfengjiang Reservoir

Global climate change is closely related to the carbon cycle, and the mechanismof the carbon source and sink has been received extensive attention of the scientificcommunity.The emission of CO2mainly comes from the burning of fossil fuels,which has been widely accepted. Reservoirs have been promoted as a clean energy allthe time. But CO2emission in some freshwater reservoirs is quite considerable, so thestudy about CO2emission in reservoirs is of great significance.Xinfengjiang Reservoir is taken as the research object here, which is the largestreservoir in the South China.78water samples are collected in the wet season and46water samples are collected in the dry season. Physicochemical properties of water(temperature, pH, electrical conductivity, dissolved oxygen,chlorophyll a) aredetermined on the spot, while the concentration of the DSi, NO3-, Alkalinity aremeasured in the lab, and pCO2is calculated with T, pH, Alkalinity and Henry’sconstant(Kh). In this paper, by analyzing and discussing the temporal and spatialvariability, influencing factors of pCO2and the diffusion flux of CO2, we gain someunderstandings as follows:The pCO2of surface water in the Xinfengjiang Reservoir is1033.55μatm and777.03μatm during the wet season and the dry season respectively, both higher thanthe atmospheric pCO2measured on the spot. In terms of verticality, the pCO2of the surface water is much higher than thewater of3m deep in the wet season, while the two layers are similar in the dry season.In terms of level changes, the pCO2of the surface water and3m deep water isincreasing during the wet season and decreasing during the dry season from the tail ofthe reservoir to the front of the dam.For the seasonal variation, the pCO2of thesurface water in the wet season is higher than in the dry season, while the pCO2of3mdeep water in the wet season is lower than in the dry season.The characteristics of the water chemistry, nutrients,dissolved carbon and pCO2are quite diverse in the different areas of the reservoir, so the study region could bedivided into the transition zone and the lacustrine zone. The controlling factors of thepCO2in the two areas are diverse.The pCO2of the surface water and the3m deepwater in the transition zone is mainly influenced by the photosynthesis ofphytoplankton during the wet season, while by respiration and the carbonate systemduring the dry season. The pCO2in the lacustrine zone is principally controlled byrespiration during the wet season, and is quite closely related to the vertical mixing ofthe water during the dry season.Xingfengjiang Reservoir’s average flux of CO2is11.2mmol m-2d-1,which is in thelow position of the world and similar to Hongfenghu Reservoir, Hongjiadu Reservoir, andWanan Reservoir.The measurement method and the grid method are used to estimatethe air-water carbon flux. The surface water of the Xifengjiang Reservoir emits17466.25t C all year round., which is the carbon source of the atmosphere.