大型浅水湖泊水-气界面CO2气体交换速率及其控制机制研究

It has been well established that carbon cycle in inland water is of great importance and lakes and other freshwater systems should be included in the global carbon cycle. Most related results have been published in the journal of Nature, Science, and PNAS. CO2 gas flux across water-air interface is driven by the difference in partial of CO2 in the water and in the air and the gas exchange velocity k, and the k value is usually derived from ocean. Gas exchange velocity k across water-air interface is driven by several factors, which showed great difference between lakes and ocean water bodies. Derived k value from ocean maybe not suitable for lake carbon flux estimate, and estimates of the magnitude of lake CO2 emissions are still questionable mostly due to the uncertainly in estimates of gas exchange velocity k. In this research, we will choose Lake Taihu, a large shallow subtropical lake in the middle and lower reaches of the Yangtze River as study area. Based on the Taihhu Eddy Flux Network, combining the filed measurements by gas tracers, floating chambers, and modeling techniques across multi spatiotemporal scales, we plan to reveal the controlling factors of gas exchange velocity k at Lake Taihu, attempt to determine the parameterization equation of the k as well as the recommended values. Furthermore, we generalize and verify the parameterization equation in others typical lakes in the middle and lower reaches of the Yangtze River. The study aims to basic theory problem in aquatic carbon cycle, applying timely data and technical supports to estimates accurately inland lakes carbon budget.

湖泊等内陆水体碳通量研究，已成为当前全球碳循环研究的前沿和热点问题，相关成果已连续在Nature、Science、PNAS等杂志上发表。目前，水体CO2通量估算，主要通过水-气界面CO2气体交换速率k乘以CO2在表层水体和大气中的分压差获得，其中k值主要来源于海洋水体。但是，k值取决于水体扰动程度等多种因素，湖泊与海洋水体具有显著的差异，直接沿用会产生较大误差，这也是目前内陆水体碳通量估算结果不确定的主要原因之一。本项目拟选取太湖为研究对象，依托我国目前仅有的湖泊（太湖）中尺度通量网，结合示踪剂气体、通量计算以及模型估算等多种方法，在不同时间和空间尺度进行闭合试验，揭示k值影响因素及其控制机制，尝试获取适合太湖水体的参数化方程和推荐数值，并在长江中下游其他湖泊推广和验证。本研究瞄准碳循环领域基础理论问题，为准确评估内陆湖泊碳收支及其在全球碳循环中的作用提供数据和技术支撑。

湖泊等内陆水体碳通量研究，已成为当前全球碳循环研究的前沿和热点问题，相关成果已连续在Nature、Science、PNAS等杂志上发表。目前，水体CO2通量估算，主要通过水-气界面CO2气体交换速率k乘以CO2在表层水体和大气中的分压差获得，其中k值主要来源于海洋水体。但是，k值取决于水体扰动程度等多种因素，湖泊与海洋水体具有显著的差异，直接沿用会产生较大误差，这也是目前内陆水体碳通量估算结果不确定的主要原因之一。本项目选取大型浅水湖泊-太湖为研究对象，开展为期三年的研究。结果表明：（1）采用风速参数可较好的表征太湖水-气界面CO2气体交换系数，太湖水-气界面CO2气体交换速率均值为1.20 m/d。(2)水体对流混合速率是水-气界面气体交换速率的关键驱动因素，且太湖水体的对流混合速率存在显著的昼夜变化特征和季节变化特征，但无显著的空间变化特征，且太湖白天时刻水体对流混合速率均值为1.00 mm/s, 夜间均值为3.98 mm/s。（3）基于水-气界面CO2交换速率的研究，结合多种观测数据得到的水体CO2分压（pCO2），表明太湖是大气CO2的排放源，年均CO2排放通量为18.2±8.4 mmol m-2 d-1（0.7±0.3 Tg yr-1），占流域初级生产力的1.3%。同时，观测数据也表明太湖水体pCO2及其CO2通量具有强烈的时空异质性。本研究给出了大型湖泊水-气界面CO2气体交换速率计算的推荐方程，明晰了富营养化湖泊（太湖）CO2源、汇功能，估算出太湖温室气体年均排放量，识别了影响温室气体排放的关键因子，为今后大型浅水湖泊水-气界面温室气体循环等相关研究提供参考和借鉴。