中国淡水生态系统甲烷排放基本特征及研究进展

本文基于中国境内的湖泊、水库、河流等淡水系统CH₄排放研究的相关成果，对203个湖泊（595个样点）、46个水库（221个样点）、112条河流（441个样点），总计1257个样点的CH₄通量数据进行统计分析，探讨了中国淡水系统（湖泊、水库、河流）CH₄排放的一般特征，总结了当前研究进展，并进一步估算和评估了中国淡水系统CH₄排放总量水平.结果表明：1）中国湖泊CH₄排放通量平均为（1.17±1.87） mg/（m²·h），蒙新湖区（（3.84±0.57） mg/（m²·h））和东北湖区（（2.62±3.54） mg/（m²·h））较高，青藏湖区（（1.94±4.13） mg/（m²·h））次之，东部湖区（（0.81±0.90） mg/（m²·h））较低，云贵湖区（（0.19±0.26） mg/（m²·h））最低；湖泊CH₄排放通量呈显著的纬度模式，高纬度地区湖泊CH₄排放高于低纬度地区；2）水库CH₄排放通量（（1.25±1.78） mg/（m²·h））与湖泊相似，水库消落带较高的排放通量（（4.34±4.45）mg/（m²·h））对水库CH₄排放具有重要贡献；3）河流CH₄排放（（0.82±1.14） mg/（m²·h））略低于湖库，长江水系CH₄排放通量（（0.98±2.38） mg/（m²·h））和黄河水系（（0.85±0.75） mg/（m²·h））相近，高于海河水系（（0.54±0.93） mg/（m²·h）），辽河、珠江水系研究较少，数据变异性极大；4）受降水、温度、径流稀释等影响，淡水系统CH₄排放呈显著的季节变化，其中湖库排放夏季高于秋季，冬春季较低，而河流则春秋季高于夏冬季；5）基于外推法估算全国湖泊、水库、河流CH₄排放总量分别约为0.96，0.29，0.76Tg/a，相当于全国湿地系统排放的75%.由于较大的时空变异性以及监测数据分布的不均匀性，目前估算存在较大的不确定性，但淡水系统CH₄排放在全球气候变化中的贡献仍不容小觑.

General characteristics and research progress of methane emissions from freshwater ecosystems in China

In this paper, we conducted a comprehensive review of the general characteristics of CH₄ emissions from China’s freshwater ecosystems based on a newly complied database. The database included CH₄ emission measurements from freshwater systems like lakes, reservoirs and rivers in China. In total, it consisted of 1257 sample points: 203 lakes (595sample), 46reservoirs (221samples), and 112 rivers (441samples). In addition, total CH₄emissions from freshwater ecosystems in China were preliminarily estimated and evaluated. The result showed that: 1) the averaged CH₄ flux of lakes in China was of (1.17±1.87) mg/(m²·h). The magnitude of CH₄ fluxes showed a great spatial variation among five lake regions in China. Lakes in Meng-xin region had the highest flux at (3.84±0.57) mg/(m²·h), followed by Northeast region ((2.62±3.54) mg/(m²·h)), Qinghai-Tibet region ((1.94±4.13) mg/(m²·h)), Eastern plain ((0.81±0.90) mg/(m²·h)) and Yun-gui region ((0.19±0.26) mg/(m²·h)). Moreover, CH₄ flux from lakes showeda significant latitude pattern, i.e. CH₄ flux increased with latitude escalating, that was contrary to the global pattern. 2) CH₄ flux in reservoirs ((1.25±1.78)mg/(m²·h)) was similar to that in lakes. Especially, the extremely higher CH₄ flux was generally found in reservoir littoral zones ((4.34±4.45) mg/(m²·h)), a big contributor to the reservoir’s total CH₄emissions. 3) Riverine CH₄ flux was (0.82±1.14) mg/(m²·h), lower than those from lakes and reservoirs. The majority of the researches on riverine CH₄ emissions were concentrated in the Yangtze River and Yellow River system, which had averaged CH₄ fluxes of (0.98±2.38) and (0.85±0.75) mg/(m²·h), respectively. Lower CH₄ emission was found in Haihe system((0.54±0.93) mg/(m²·h)), and scattered researches focused on Liaohe and Pearl River systems, which might lead to a high degree of variations in those CH₄ emission data points. 4) CH₄ fluxes in freshwater systems of China also showed a seasonal variation. CH₄ fluxes from lakes and reservoirs were higher in summer, while riverine CH₄ fluxes were higher in spring and autumn than summer and winter. Such seasonal variations were probably affected by precipitation, temperature, and runoff dilution.5) Based on universal extrapolation, we roughly estimated the total CH₄ emissions from all lakes, reservoirs and rivers in China were 0.96, 0.29, 0.76Tg/a, respectively, with a total of 2.01 Tg/a, equivalent to 75% of the total CH₄ emission from China wetland systems. Given the strong spatiotemporal variability and the uneven distribution of monitoring data, our estimation had a large uncertainty. Nonetheless, we concluded that CH₄ flux in Chinese freshwater system was a contributor to regional carbon budget and global greenhouse gas emission.