Quantifying Event-Driven Methane Fluxes from Northern Peatlands Using A Novel Automated Flux Chamber Technique

泥炭地是温室气体甲烷（CH4）的最大天然来源，了解泥炭地对大气CH4收支的潜在贡献对于了解当前和未来的气候变化至关重要。泥炭地的甲烷是被称为“产甲烷菌”的厌氧微生物分解有机物的副产品。这些生物通常生活在更深、更饱和的泥炭层中，这些泥炭层从大气中接受很少或根本没有氧气输入。甲烷也会被一群被称为“甲烷氧化菌”的土壤微生物破坏，它们需要氧气将甲烷分解成二氧化碳。这些生物通常居住在靠近土壤-大气界面的上层泥炭层（0-10厘米），在那里O2与下面的基质交换更自由。因此，泥炭地CH4净排放受到产甲烷菌产生CH4和氧化甲烷菌分解CH4的相对平衡的影响。泥炭地CH4循环中一个关键的未解问题是天气事件对大气中CH4排放的影响程度。天气事件触发关键环境变量的变化，如大气压力、降雨、土壤湿度和土壤氧（O2）状态，所有这些都在调节CH4净排放中发挥作用。大气压力可以强烈影响以气泡形式从泥炭中释放的CH4的数量，这一过程被称为“沸腾”。CH4是一种疏水气体，倾向于以气泡的形式积聚在泥炭中，而不是溶解在土壤孔隙水中。由于气旋天气系统的通过引起的大气压力的突然下降可以触发气泡释放，因为大气压力的降低刺激CH4从土壤孔隙水中脱气。此外，根据理想气体定律，大气压力的降低会导致相对体积更大的气泡的形成，这可能会进一步增强沸腾。降雨事件也在调节CH4排放中发挥作用，因为土壤上层（0-10 cm）的淹没通常会降低土壤O2浓度，抑制甲烷氧化菌的活性。甲烷氧化菌分解CH4的速率降低意味着更多的CH4被排放到大气中，而不是转化为二氧化碳。由于未能充分量化或描述大气压力和降雨事件的影响，我们很可能严重低估了泥炭地甲烷的排放量。例如，对CH4沸腾的研究表明，泥炭地总CH4排放中多达50- 60%可能来自冒泡（而不是通过通气植物的扩散或运输），其中大部分排放是由于大气压力的降低而发生的。同样，降雨事件可引起CH4排放的急剧增加，否则会破坏大气中CH4的区域成为短暂的CH4源。我们对天气事件对甲烷排放的影响所知甚少的原因是，这些现象是短暂的和偶发的，因此很难用传统的测量技术进行研究。由于天气事件的不可预测性和短暂性，研究它们的唯一合适方法是收集随时间变化的CH4通量的连续测量值。然而，使用传统的采样方法收集CH4排放的连续测量值在经济上和后勤上都很困难，因为这些方法是时间和劳动密集型的。为了解决这个问题，我们开发了一种新型的自动化通量室技术，能够准连续地测量CH4排放，用户干预和耗材需求最小。我们建议使用这个新系统来量化大气压力和降雨事件对泥炭地CH4排放的影响，从而提高我们对控制CH4向大气通量的过程的总体理解。

Peatlands are the largest natural sources of the greenhouse gas methane (CH4), and understanding the potential contributions of peatlands to atmospheric CH4 budgets is crucial for understanding current and future climate change. Methane in peatlands is produced as a by-product of organic matter decomposition by anaerobic microorganisms called 'methanogens.' These organisms typically inhabit deeper, more saturated peat layers that receive little or no O2 input from the atmosphere. Methane is also destroyed by a group of soil microorganisms called 'methanotrophs,' which require O2 to breakdown CH4 to CO2. These organisms typically inhabit the upper peat horizons (0-10 cm) near the soil-atmosphere interface, where O2 exchanges more freely with the substrate below. Peatland net CH4 emissions are thus influenced by the relative balance of CH4 production by methanogens and CH4 breakdown by methanotrophs. One of the key unanswered questions in peatland CH4 cycling is the extent to which weather events influence CH4 emissions to the atmosphere. Weather events trigger changes in key environmental variables, such as atmospheric pressure, rainfall, soil moisture, and soil oxygen (O2) status, all of which play a role in regulating net CH4 emissions. Atmospheric pressure can strongly influence the amount of CH4 released from peat in bubble form, a process referred to as 'ebullition.' CH4 is a hydrophobic gas that tends to accumulate in peat as bubbles, rather than dissolving into soil pore waters. Sudden drops in atmospheric pressure caused by the passage of cyclonic weather systems can trigger bubble release because reductions in atmospheric pressure stimulates CH4 to de-gas from soil pore waters. In addition, reductions in atmospheric pressure result in the formation of bubbles with larger relative volumes, in accordance with the Ideal Gas Law, which may further enhance ebullition. Rainfall events also play a role in regulating CH4 emissions because inundation of upper soil horizons (0-10 cm) often reduces soil O2 concentrations, suppressing the activity of methanotrophs. Lowered rates of CH4 breakdown by methanotrophs means that more CH4 is emitted to the atmosphere, rather than being converted to CO2. It is likely that we are significantly underestimating peatland CH4 emissions by failing to adequately quantify or characterise the effects of atmospheric pressure and rainfall events. For example, studies of CH4 ebullition suggest that as much as 50-60 % of total peatland CH4 emissions can arise from bubbling (as opposed to diffusion or transport through aerenchymatic plants), with most of those emissions occurring because of reductions in atmospheric pressure. Likewise, rainfall events can cause dramatic increases in CH4 emissions, with areas that would otherwise destroy atmospheric CH4 becoming transient CH4 sources. The reason that we know so little about the effects of weather events on CH4 emissions is that these phenomena are transient and episodic, making them difficult to study using conventional measurement techniques. Because of the unpredictable and transient nature of weather events, the only suitable means of studying them is to collect continuous measurements of CH4 flux over time. However, it is financially and logistically difficult to collect continuous measurements of CH4 emissions using conventional sampling methodologies because these approaches are time and labour intensive. To address this problem, we have developed a novel automated flux chamber technique capable of measuring CH4 emissions quasi-continuously, with minimal user intervention and demand for consumables. We propose to use this novel system to quantify the effects of atmospheric pressure and rainfall events on peatland CH4 emissions, thus improving our overall understanding of the processes governing CH4 flux to the atmosphere.