Growing season, non-growing season and annual CH4 fluxes from temperate, boreal, and Arctic wetlands and uplands@en

Wetlands are the single largest natural source of atmospheric methane (CH4), a greenhouse gas, and occur extensively in the northern hemisphere. Large discrepancies remain between bottom-up and top-down estimates of northern CH4 emissions. To explore whether these discrepancies are due to poor representation of non-growing season CH4 emissions, we synthesized non-growing season and annual CH4 flux measurements from temperate, boreal, and tundra wetlands and uplands. Median non-growing season wetland emissions ranged from 0.9 g m-2 in bogs to 5.2 g m-2 in marshes and were dependent on moisture, vegetation, and permafrost. Annual wetland emissions ranged from 0.9 g m-2 y-1 in tundra bogs to 78 g m-2 y-1 in temperate marshes. Uplands varied from CH4 sinks to CH4 sources with a median annual flux of 0.0 ± 0.2 g m-2 y-1. The measured fraction of annual CH4 emissions during the non-growing season (observed: 13 to 47%) was significantly larger than was predicted by two process-based model ensembles, especially between 40-60º N (modeled: 4 to 17%). Constraining the model ensembles with the measured non-growing fraction increased total non-growing season and annual CH4 emissions. Using this constraint, the modeled non-growing season wetland CH4 flux from >40° north was 6.1 ± 1.5 Tg y-1, three times greater than the non-growing season emissions of the unconstrained model ensemble. The annual wetland CH4 flux was 37 ± 7 Tg y-1 from the data-constrained model ensemble, 25% larger than the unconstrained ensemble. Considering non-growing season processes is critical for accurately estimating CH4 emissions from high latitude ecosystems, and necessary for constraining the role of wetland emissions in a warming climate. This dataset contains the synthesis of measured flux data from the study.湿地是大气甲烷（CH₄，一种温室气体）最主要的天然排放源，且在北半球广泛分布。当前北半球甲烷排放的自下而上估算（bottom-up estimates）与自上而下估算（top-down estimates）结果仍存在显著差异。为探究这些差异是否源于非生长季（non-growing season）甲烷排放的表征不足，我们整合了温带、寒带、苔原湿地与旱地的非生长季及年际甲烷通量观测数据。湿地非生长季甲烷排放的中位数范围为泥炭沼泽（bog）的0.9 g·m⁻²至沼泽（marsh）的5.2 g·m⁻²，其排放水平受湿度、植被与永久冻土的影响。年际湿地甲烷排放范围从苔原泥炭沼泽的0.9 g·m⁻²·y⁻¹至温带沼泽的78 g·m⁻²·y⁻¹。旱地的甲烷通量既可为汇也可为源，年通量中位数为0.0 ± 0.2 g·m⁻²·y⁻¹。观测得到的非生长季甲烷排放占年总排放的比例为13%至47%，显著高于两组基于过程的模型集合（process-based model ensemble）的预测结果，尤其在北纬40°至60°区域，模型预测的占比仅为4%至17%。利用实测的非生长季排放占比对模型集合进行约束后，模型估算的非生长季及年际甲烷总排放量均有所提升。经该约束后，北纬40°以北区域的湿地非生长季甲烷通量估算值为6.1 ± 1.5 Tg·y⁻¹，是未约束模型集合估算值的3倍。经数据约束的模型集合得到的年际湿地甲烷通量为37 ± 7 Tg·y⁻¹，较未约束集合提升25%。考虑非生长季过程对于精准估算高纬度生态系统的甲烷排放至关重要，同时也是约束湿地排放在气候变暖过程中作用的必要前提。本数据集包含本研究整合的实测通量汇总数据。