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预算的潜在贡献对于了解当前和未来的气候变化至关重要。泥炭地中的甲烷是由一种叫做产甲烷菌的厌氧微生物分解有机物的副产品。“这些生物通常栖息在更深、更饱和的泥炭层中，这些泥炭层很少或根本没有从大气中获得氧气。甲烷也会被一组称为“甲烷氧化菌”的土壤微生物破坏，它们需要O2将CH4分解为CO2。这些生物通常栖息在土壤-大气界面附近的泥炭层（0 - 10厘米），在那里氧气与下面的基质交换更自由。因此，泥炭地的净甲烷排放量的甲烷生产和甲烷氧化菌的甲烷分解的相对平衡的影响。泥炭地甲烷循环的一个关键的未回答的问题是天气事件影响甲烷排放到大气中的程度。天气事件触发了关键环境变量的变化，如大气压力、降雨量、土壤湿度和土壤氧（O2）状况，所有这些都在调节CH4净排放量方面发挥作用。大气压力会强烈影响泥炭以气泡形式释放的甲烷量，这一过程被称为"沸腾"。甲烷是一种疏水性气体，倾向于以气泡的形式在泥炭中积累，而不是溶解到土壤孔隙沃茨。气旋天气系统通过造成的大气压力突然下降可触发气泡释放，因为大气压力的降低刺激土壤孔隙沃茨中的甲烷脱气。此外，根据理想气体定律，大气压力的降低导致形成具有较大相对体积的气泡，这可以进一步增强沸腾。降雨事件也发挥了调节甲烷排放的作用，因为土壤上层（0 - 10厘米）的淹没往往会降低土壤O2浓度，抑制甲烷氧化菌的活动。甲烷氧化菌分解甲烷的速率降低意味着更多的甲烷被排放到大气中，而不是转化为二氧化碳。我们很可能由于未能充分量化或解释大气压力和降雨事件的影响而大大低估了泥炭地的甲烷排放量。例如，对甲烷沸腾的研究表明，泥炭地甲烷总排放量的50 - 60%可能来自沸腾（与通过通气组织植物的扩散或运输相反），其中大部分排放是由于大气压力的降低。同样，降雨事件可能导致甲烷排放量急剧增加，否则会破坏大气中甲烷的地区成为短暂的甲烷源。我们对天气事件对甲烷排放的影响知之甚少的原因是，这些现象是短暂的和偶发的，因此很难使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，研究它们的唯一适当手段是收集一段时间内CH4通量的连续测量值。然而，使用传统的取样方法收集甲烷排放量的连续测量值在资金和后勤上都很困难，因为这些方法需要大量的时间和劳动力。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排放量，最大限度地减少用户干预和对耗材的需求。我们建议使用这种新的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CH4通量到大气中的过程的整体理解。

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.