Methane fluxes from seasonally flooded forests in the Amazon basin

甲烷（CH 4）是一种强烈的温室气体，其大气浓度自工业化前时代以来几乎增加了两倍。天然湿地是有机物质厌氧分解产生甲烷的主要来源。南美洲的亚马逊河流域大部分被湿地覆盖，是热带CH 4排放的一个关键地区。尽管它对全球甲烷预算的重要性，亚马逊盆地的总甲烷排放量没有很好地量化，个别甲烷源没有得到很好的理解。亚马逊河流域“自下而上”（按比例放大各个排放源）的甲烷排放量估计数与“自上而下”（反演大气浓度测量值）的排放量估计数相差2倍。湿地，如季节性泛滥的森林，是甲烷排放的关键区域，但测量数据很少。本提案的总体目标是了解季节性水淹林对亚马逊CH 4预算的作用。在一个季节性淹没的森林植被冠层CH 4通量测量将进行至少一年。这一重要空间尺度的测量目前尚不存在，但可以将“自下而上”研究中使用的单个源的排放量与“自上而下”的估计数联系起来，后者提供了一个区域的综合通量。冠层以上的测量将由其足迹内的单个源测量补充。这一测量组合使得能够将各个源的排放量与树冠上方测量的通量联系起来;因此，调查区域的CH 4收支将是封闭的。这一点很重要，因为有些排放源非常不确定，例如，最近，被水淹没的树干的排放量被认为是迄今为止被忽视的一个大的CH 4排放源。此外，在一个完整的年周期以上的冠层CH 4通量测量提供了一个综合通量的季节性淹没的森林，可以放大与“自上而下”的估计进行比较。建议在K34塔进行测量，该塔位于靠近马瑙斯（巴西）的季节性洪水森林中。在这个独特的基础设施上安装我们的仪器设备可以完全进入，其中不仅包括塔，还包括仪器设备的空调外壳。对于通量测量，我们将使用弛豫涡流累积（REA）技术耦合到FTIR光谱仪。该FTIR-REA通量测量系统的设置是在欧盟项目INGOS中开发的。该系统能够同时测量CH_4、CO_2、N_2O、CO和d_13CO_2的排放通量。将使用便携式气体分析仪对通量测量足迹内的各个排放源进行周期性测量。

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.