环境地球化学国家重点实验室知识库

The Xinanjiang Reservoir (E118°42′–E118°59′, N29°28′–N29°58′), has a surface area of 567 km², with a mean water depth of 34 m, and is in an oligotrophic state at present. In this study, five cruises were carried out in April, June, August and November 2010, and January 2011, to understand the seasonal variation of CO₂emission and to estimate the annual diffusion flux of CO₂ from this reservoir. The partial pressure of CO₂ (pCO₂) in surface water was determined using a continuous measurement system (equilibrator-infrared system) from upstream to central reservoir, and pCO₂ along the water column in central reservoir and in downstream of the dam was also determined. Results showed that pCO₂ in reservoir surface water varied significantly in different seasons, ranging from 5 μatm in August to 1700 μatm in January; while in downstream of the dam, it ranged from 1400 μatm in April to 3800 μatm in August. Along the water column in central reservoir, pCO₂also showed significantly variations seasonally, and a water mass with quite high pCO₂ (>4000 μatm) formed below water depth of 20 m in warm seasons. The highest diffusion flux of CO₂ (F–CO₂) appeared in January, with values of 20.9 mmol m⁻² d⁻¹at river reach and 25.2 mmol m⁻² d⁻¹ at central reservoir, while the lowest values of F–CO₂ were −10.0 at river reach and −10.8 mmol m⁻² d⁻¹ at central reservoir in August. Downstream of the dam had quite high positive F–CO₂ during the whole year, with a range of 129.1 in April to 381.5 mmol m⁻² d⁻¹ in August. In total, about 88.9 kton a⁻¹ CO₂ was emitted to the atmosphere from the Xinanjiang Reservoir surface, while 39% of it (35.1 kton a⁻¹) was absorbed by surface water in warm seasons. Downstream and turbine had a comparable CO₂ outgas flux of 61.5 kton a⁻¹. When taking the whole reservoir surface, turbine and downstream into account, the Xinanjiang Reservoir system had a net CO₂ emission flux of 115.3 kton a⁻¹.