Wetland contribution to interannual variability in atmospheric methane growth rate

甲烷（CH4）是人类社会的重要能源，也是一种能够改变地球气候的强效温室气体。对自然和人类向大气释放的甲烷进行量化是一项挑战，但对于各国核实减少温室气体排放的目标是否正在实现是必要的。沼泽、沼泽、沼泽和沼泽等湿地是向大气排放甲烷的最大天然来源。在前工业化时代，天然湿地是地球大气中甲烷的主要来源，并将继续是甲烷的一个关键的长期来源，形成了人类甲烷排放叠加的自然大气背景，必须加以识别。甲烷中碳和氢的重同位素和轻同位素数量的细微差异可以用来“指纹”来自不同来源的排放，包括不同类型的湿地。对排放源的可靠识别增强了我们量化区域和全球排放源逐年变化的能力。它还可以检测来源的变化，例如像湿地这样的巨大全球生态系统是否以一种可能进一步增加地球大气中甲烷和二氧化碳含量的方式对气候变化作出反应。***湿地同位素变化的自然模式仍在出现，特别是氢同位素，由于分析方面的挑战，迄今尚未对其进行广泛研究。该研究项目将采用加拿大首个新型激光仪器，同时测量湿地地下的碳和氢同位素组成及其向大气的排放。确定甲烷排放同位素组成与湿地类型之间的关系。环境变量的影响和气体输运过程对甲烷同位素比值的影响也将被表征。这些数据将被纳入全球模型，以改进对湿地对大气甲烷浓度贡献的估计，并增进对湿地在影响地球大气中甲烷年增率变化方面所起作用的认识。更详细地了解这些重要的自然生态系统的排放情况，将能够更准确地量化人类活动，特别是生物源的甲烷释放，因为目前仅使用碳同位素无法对其排放进行明确的“指纹识别”。基于稳定碳和氢同位素的双同位素方法的发展将提供较少模糊的来源特征，并有助于改进全球甲烷循环预算。

Methane (CH4) is an important energy source for human society but also a potent greenhouse gas capable of altering Earth's climate. Quantifying natural and human release of methane to the atmosphere is challenging but necessary in order for nations to verify that targets are being met for reducing greenhouse gas emissions. *** Wetlands such as bogs, fens, marshes and swamps are the largest natural source of methane emissions to the atmosphere. During pre-industrial times, natural wetlands were the dominant source of methane in Earth's atmosphere and continue to be a key perennial source of methane that forms the natural atmospheric background on which human methane emissions are superimposed and must be discerned. Subtle differences in the quantities of heavy and light isotopes of carbon and hydrogen in methane can be used to 'fingerprint' emissions from different sources, including different types of wetland. Reliable identification of sources enhances our ability to quantify year-to-year changes in emission sources both regionally and globally. It also enables detection of change in sources such as whether vast global ecosystems like wetlands are responding to climate change in a manner that may further increase the amount of methane and carbon dioxide in Earth's atmosphere. *** Natural patterns of isotopic variation in wetlands are still emerging, in particular for hydrogen isotopes, which have not been studied extensively to date because of analytical challenges. This program of research will employ new laser instrumentation, the first of its type in Canada, to measure both carbon and hydrogen isotope compositions simultaneously in the subsurface of wetlands and their emissions to the atmosphere. Relationships between the isotope composition of methane emissions and wetland type will be determined. The influence of environmental variables and the role of gas transport process that alter isotope ratios in methane also will be characterized. The data will be integrated into global models to refine estimates of the contribution of wetlands to the atmospheric concentration of methane and to improve understanding of the role that wetlands play in influencing year-to-year changes in the rate at which methane is increasing in Earth's atmosphere. A more detailed knowledge of emissions from these important natural ecosystems will enable more accurate quantifications of methane release from human activities, in particular, biological sources because their emissions at present cannot be fingerprinted' unambiguously using only carbon isotopes. Development of a dual isotope approach based upon both stable carbon and hydrogen isotopes will provide less ambiguous source signatures and help to refine the global methane cycle budget.