亚热带地区浅水湖泊水体CO2和CH4排放特征及影响因素研究——以巢湖为例

Lakes were identified as important atmospheric carbon dioxide and methane sources. Terrestrial carbon sink can partly offset by global lake carbon emissions. Currently, the research about lake carbon emissions focus on tropic zones, temperate zones and acrtic, less study has been done in subtropical zones where suffered intense human activities. Taking a typical large shallow lake (Lake Chaohu) in subtropical zone of east China as a research subject: 1) the comparative observations of lake carbon dioxide and methane fluxes with floating chamber method, diffusion model method and inverted funnels method will be done for identifying the main emission way (plant transport, molecular diffusion or ebullition) of carbon dioxide and methane from lake. Otherwise, the spatial-temporal variability of carbon dioxide and methane from lake will be explored.2) In order to reveal the key factors which control carbon dioxide and methane emissions, the relationships between physical and chemical indices of lake water (water temperature, water depth, lake water pH, nutrient concentrations and so on) and carbon dioxide and methane emissions will be analyzed using mathematical statistics analysis methods such as Multiple Linear Regression Analysis, Redundancy Analysis and Path Analysis. 3) Based on the data of carbon dioxide and methane emission and the distribution area of dominant aquatic plants in Lake Chaohu during the measurement period, this project preliminary assesses total annual carbon dioxide and methane emissions from Lake Chaohu at the current stage. This study will help us to understand the mechanisms of carbon gases emission from lake located in subtropical zone. At the same time, it will provide basic data and theoretical foundation for accurately assessing regional carbon budget.

湖泊水体是重要的大气CO2和CH4排放源，其排放能抵消部分陆地碳汇，当前对湖泊水体碳排放研究多集中在热带、温带和寒带地区，对人类活动扰动强烈的亚热带地区关注较少。项目选取亚热带地区典型浅水湖泊-巢湖为研究对象：1）利用漂浮箱法、扩散模型法以及倒置漏斗法进行碳通量对比观测，判定湖泊水体CO2和CH4排放的主要途径（植物传输、分子扩散还是气泡？），明晰湖泊水体CO2和CH4排放的时空变异特征；2）采用多元线性回归分析、冗余分析和通径分析等方法，揭示水温、水深、水体pH及养分浓度等湖泊水体理化性质与CO2和CH4排放间的关系，识别影响湖泊水体CO2和CH4排放时空变异的关键因子；3）基于项目期（2年）巢湖水体碳通量观测数据，结合同时段巢湖优势水生植物的分布面积，估算巢湖水体CO2和CH4年排放总量。开展此研究有助于深入认识亚热带地区湖泊水体碳排放机理，为精确评估区域碳收支提供基础数据和理论基础。

湖泊水体是重要的大气CH4和CO2排放源，其排放能抵消部分陆地碳汇，当前对湖泊水体碳排放研究多集中在热带、温带和寒带地区，对人类活动扰动强烈的亚热带地区关注较少。在本项目的资助下，选取了亚热带地区大型富营养化浅水湖泊-巢湖为研究对象，开展了为期3年的CH4和CO2排放通量的监测研究。结果表明：（1）巢湖水体是重要的CH4排放源，平均扩散排放速率约为0.251 mg m-2 h-1，平均冒泡排放速率约为10.945 mg m-2 h-1，气泡释放是巢湖水体CH4释放至大气中的主要途径，CH4排放冒泡通量约占总排放通量的72%。巢湖水体既是CO2源，也是CO2汇，不同观测方法获得的观测结果并不一致，有待进一步深入研究。（2）巢湖水体CH4和CO2排放具有显著的时空变异特征，时间上表现为CH4和CO2扩散排放峰值出现在夏季，空间上表现为西湖区CH4和CO2排放显著高于东、中湖区，近岸带排放高于湖心区。（3）溶解氧、温度（气温、水温、底泥温度）、风速和大气压对CH4排放的时空变异存在显著影响，CO2通量在不同年际间的影响因素不一，一般受到溶解氧、pH和水温的控制。（4）观测期内，巢湖水体CH4年排放量在9.02-18.05 GgC yr-1范围内波动，而对于CO2来说，2018年巢湖水体排放61.47 GgC,2019年吸收了29.18 GgC，可见CH4排放在巢湖水体碳循环过程中占有重要的地位。开展此研究有助于加深了人们对亚热带地区湖泊水体碳排放机理的认识，为精确评估区域碳收支提供基础数据和理论基础。