青海湖水-气界面CO2交换的地球化学研究

针对内陆水体CO2释放的boundless碳循环模型是当前全球碳循环研究的前沿，其中盐湖是重要的组成部分，也是最薄弱的环节，目前仅有少量观测数据且争议很大。本次研究选取我国最大的微咸水湖青海湖及其周围的小湖泊作为研究对象，利用野外现场观测水-气界面CO2交换，结合走航式表层水体CO2浓度测定，充分揭示盐湖CO2时空分布的高变化性特征，准确估算水气界面CO2交换通量。通过对湖水颗粒有机碳、溶解有机碳、溶解无机碳和颗粒无机碳的浓度和同位素系统分析，揭示青海湖有机碳、无机碳的生物地球化学过程，认识微咸水湖OC、IC循环的相互作用对界面CO2交换的调控机制，建立以水-气界面CO2交换为核心的湖泊碳质量平衡模型。对比分析青海湖主湖与周围不同盐度小湖泊的CO2变化规律，认识盐湖演化以及未来全球变化背景下盐湖CO2交换的变化趋势。研究成果将为认识盐湖在区域及全球碳循环中的作用奠定坚实的基础。

Constructing “boundless carbon cycle”, designating all lateral and vertical carbon fluxes to and from the systems of inland waters, is the most fundamental frontier of the global carbon cycling study. Much progress has been made about the fluxes of CO2 emission from rivers, streams, lakes, reservoirs, ponds and other systems of inland waters around the world. However, data from salt lakes remains very sparse. As a result, the role of salt lakes as carbon source or sink in global carbon cycling, the strength of carbon source/sink, keeps to be disputed extensively and intensely. And factors and processes regulating CO2 production and emission in salt lakes remains unknown. In this proposal, we will conduct an observation of CO2 exchange on the water-atmosphere interface at Lake Qinghai, a huge water body with a salinity of about 15.5‰, using a static chamber technique. Combining with measurements of CO2 partial pressure in the surface water, the flux of CO2 exchange on the water-atmosphere interface in Lake Qinghai and surrounding small lakes could be calculated with a better precision. The concentrations and isotopic compositions of particulate organic C (POC), dissolved organic carbon (DOC), dissolved inorganic carbon (DIC) and particulate inorganic carbon (PIC) of lake samples that are collected at the different depth in the water columns of the lake will be determined. Processes of biogeochemical cycling of organic carbon and inorganic carbon will be discussed on the basis of temporal and spatial variations of concentration and isotopes of POC, DOC, DIC and PIC, with a focus on the coupling among organic carbon cycling, inorganic carbon cycling, and pH variation. The mechanism of how biogeochemical cycling of organic carbon and inorganic carbon regulate the CO2 concentrations and exchange fluxes in the salt lake will be revealed. A model based on the balance of carbon mass will be constructed, in which CO2 exchange on the water-atmosphere interface will be coupled with organic and inorganic carbon cycling. A comparison of CO2 concentrations and exchange fluxes between Lake Qinghai and surrounding small lakes whose salinity varies in a large range will be carried out, by which change of CO2 exchange flux on the water- atmosphere interface of salt lakes with evolution in the past and trend in the future of salt lakes will be discussed. Finally, the role of salt lakes to the local and global carbon cycling will be assessed on the basis of the result that will be obtained in this program.