Wetland contribution to interannual variability in atmospheric methane growth rate

点击翻译按钮获取中文摘要

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.