Methane fluxes from seasonally flooded forests in the Amazon basin

甲烷(CH4)是一种强烈的温室气体，与前工业化时代相比，其大气浓度几乎增加了两倍。自然湿地是甲烷的主要来源，甲烷是有机物质厌氧分解产生的。南美洲的亚马逊盆地大部分被湿地覆盖，是热带甲烷排放的关键地区。尽管它对全球甲烷预算很重要，但亚马逊盆地的甲烷排放总量没有得到很好的量化，个别甲烷的来源也没有得到很好的理解。亚马逊盆地的“自下而上”(个别来源的向上标度)CH4排放估计值与“自上而下”(大气浓度测量倒置)估计值相差2倍。湿地，如季节性洪水泛滥的森林，是甲烷排放的关键地区，但测量数据很少。这项提案的总体目标是了解季节性洪灾森林在亚马逊甲烷预算中的作用。季节性淹水森林中的冠层以上CH4通量的测量将至少持续一年。这一重要空间尺度的测量目前还不存在，但允许将“自下而上”研究中使用的个别源的排放量与“自上而下”的估计值联系起来，后者提供了一个区域的综合通量。上面的冠层测量将由其足迹内的单个源测量来补充。这一测量组合允许将单个污染源的排放量与在树冠上方测量的通量联系起来；因此，调查区域的CH4预算将关闭。这一点很重要，因为一些来源非常不确定，例如最近，被淹的树干的排放被认为是迄今为止被忽视的一个巨大的CH4来源。此外，在一个完整的年度周期中，冠层以上CH4通量的测量为季节性洪水淹没的森林提供了一个综合通量，该通量可以被放大，以便与“自上而下”的估计进行比较。测量将在K34塔进行，该塔位于巴西马瑙斯附近季节性洪水泛滥的森林中。我们提供了在这个独特的基础设施安装我们的仪器的完全通道，该基础设施不仅包括塔楼，还包括仪器的空调外壳。对于通量的测量，我们将使用一种与FTIR光谱仪耦合的松弛涡流积累(REA)技术。FTIR-REA通量测量系统的设置是在欧盟项目INGOS内开发的。该系统能同时测量CH4、CO2、N2O、CO和DEL13CO2的通量。流量测量足迹内的各个排放源将使用便携式气体分析仪按战役进行测量。

Methane (CH4) is a strong greenhouse gas and its atmospheric concentration has nearly tripled since pre-industrial times. Natural wetlands are a major source of methane, which is produced by the anaerobic decomposition of organic material. The Amazon basin in South America is largely covered by wetlands and is a key region for tropical CH4 emissions. Despite its importance for the global methane budget, the overall CH4 emission from the Amazon basin is not well quantified and the individual CH4 sources are not well understood. The Amazon basin's 'bottom-up' (upscaling of individual sources) CH4 emission estimate differs by a factor 2 from the 'top-down' (inversion of atmospheric concentration measurements) emission estimate. Wetlands, such as the seasonally flooded forests, are key regions for methane emissions, but measurements are sparse. The overall objective of this proposal is to understand the role of seasonally flooded forests for the Amazonian CH4 budget. Above-canopy CH4 flux measurements in a seasonally flooded forest will be performed over at least one year. Measurements of this important spatial scale do currently not exist, but allow linking emissions of the individual sources used in 'bottom-up' studies with 'top-down' estimates, which provide the integrated flux for a region. The above-canopy measurements will be complemented by individual source measurements within its footprint. This combination of measurements allows linking the emissions of the individual sources with the fluxes measured above the canopy; hence the CH4 budget will be closed for the investigated area. This is important, because some sources are very uncertain, e.g. very recently, emissions from flooded tree stems have been suggested as a large hitherto disregarded CH4 source. Furthermore the above-canopy CH4 flux measurements over a full annual cycle provide an integrated flux for seasonally flooded forests that can be upscaled for comparison with the 'top-down' estimates. The measurements are proposed to take place at the K34 tower, which is located in a seasonally flooded forest close to Manaus (Brazil). Full access has been offered to install our instrumentation at this unique infrastructure, which contains not only the tower, but also air-conditioned housing for the instrumentation. For the flux measurements we will use a Relaxed Eddy Accumulation (REA) technique coupled to an FTIR-spectrometer. The setup of this FTIR-REA flux measurement system has been developed within the EU-project INGOS. This system is able to measure the fluxes of CH4, CO2, N2O, CO and del13CO2 simultaneously. The individual emission sources within the footprint of the flux measurements will be measured on campaign basis using a portable gas analyzer.