Department of Environmental and Biological Sciences, University of Eastern Finland, Kuopio, Finland.
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
Glob Chang Biol. 2018 Aug;24(8):3331-3343. doi: 10.1111/gcb.14137. Epub 2018 Apr 25.
Wetlands are the single largest natural source of atmospheric methane (CH ), a greenhouse gas, and occur extensively in the northern hemisphere. Large discrepancies remain between "bottom-up" and "top-down" estimates of northern CH emissions. To explore whether these discrepancies are due to poor representation of nongrowing season CH emissions, we synthesized nongrowing season and annual CH flux measurements from temperate, boreal, and tundra wetlands and uplands. Median nongrowing season wetland emissions ranged from 0.9 g/m in bogs to 5.2 g/m in marshes and were dependent on moisture, vegetation, and permafrost. Annual wetland emissions ranged from 0.9 g m year in tundra bogs to 78 g m year in temperate marshes. Uplands varied from CH sinks to CH sources with a median annual flux of 0.0 ± 0.2 g m year . The measured fraction of annual CH emissions during the nongrowing season (observed: 13% to 47%) was significantly larger than that was predicted by two process-based model ensembles, especially between 40° and 60°N (modeled: 4% to 17%). Constraining the model ensembles with the measured nongrowing fraction increased total nongrowing season and annual CH emissions. Using this constraint, the modeled nongrowing season wetland CH flux from >40° north was 6.1 ± 1.5 Tg/year, three times greater than the nongrowing season emissions of the unconstrained model ensemble. The annual wetland CH flux was 37 ± 7 Tg/year from the data-constrained model ensemble, 25% larger than the unconstrained ensemble. Considering nongrowing season processes is critical for accurately estimating CH emissions from high-latitude ecosystems, and necessary for constraining the role of wetland emissions in a warming climate.
湿地是大气甲烷（CH ）的最大自然源之一，CH 是一种温室气体，在北半球广泛存在。北部 CH 排放的“自下而上”和“自上而下”估计之间仍然存在很大差异。为了探讨这些差异是否是由于非生长季节 CH 排放的代表性不足造成的，我们综合了来自温带、北方和苔原湿地和旱地的非生长季节和年 CH 通量测量值。非生长季节湿地排放量的中位数范围从沼泽的 0.9 g/m 到泥沼的 5.2 g/m ，取决于水分、植被和永冻层。年湿地排放量范围从苔原沼泽的 0.9 g/m 年到温带泥沼的 78 g/m 年。旱地的 CH 汇或源，年通量中位数为 0.0 ± 0.2 g/m 年 。非生长季节年 CH 排放量的实测比例（实测：13%至 47%）明显高于两个基于过程的模型集合的预测值，特别是在 40°至 60°N 之间（模型预测：4%至 17%）。用实测的非生长季节分数来约束模型集合会增加非生长季节和年 CH 排放总量。使用该约束条件，来自北纬>40°的模型约束湿地非生长季 CH 通量为 6.1 ± 1.5 Tg/年，是未约束模型集合非生长季排放量的三倍。数据约束模型集合的年湿地 CH 通量为 37 ± 7 Tg/年，比未约束集合大 25%。考虑非生长季节过程对于准确估计高纬度生态系统的 CH 排放至关重要，也是约束湿地排放对变暖气候的作用所必需的。
