Collaborative Research: Modeling and Measuring the Spatio-Temporal Variability of Methane Emissions from Tropical Dambo Wetlands

从分子上看，在100年的时间尺度上，甲烷（CH4）作为温室气体的效率是二氧化碳（CO2）的30倍左右。天然湿地是全球甲烷排放的最大单一来源，也是对气候变化做出直接反应的唯一来源。尽管甲烷意义重大，但对全球天然湿地甲烷排放量的估计存在很大的不确定性。由于大多数发展中国家缺乏地面观测、详细地图和数据，热带湿地（占湿地排放的大部分）的不确定性尤其大。Dambos（季节性饱和、无通道的谷底）构成了非洲中部和南部最大的季节性湿地地理范围，占据了中非高原的20%，总面积超过20万平方公里。该项目的目标是对乌干达卢韦罗北部2500平方公里代表性丹博斯的甲烷排放量进行空间和时间上的明确估计。研究人员将使用多光谱（ASTER）遥感结合数字地形建模对景观进行分层，区分丹博湿地与高地地区，以及丹博湿地内的土壤和水文变化。将选择有代表性的地点进行详细的土壤和植被特征、水文和温度监测以及甲烷通量的测量。项目小组将通过一个主要的雨季监测甲烷通量，并在一年半或三个雨季监测水文。利用这些数据，他们将确定丹波甲烷通量的关键控制因素，并构建一个将这些通量与土壤性质、植被、温度和水文联系起来的经验模型。该项目将首次对丹博湿地的甲烷排放量进行严格量化，为整个非洲中部和南部热带丹博湿地的年度和季节性甲烷排放量的一级估计提供基础。这些数据将有助于限制高度不确定的全球大气甲烷模型的热带源估计。采用的建模策略“将剖面尺度的甲烷模型与动态景观湿地模型联系起来”支持对热带丹博湿地对未来气候变化情景的响应的预测，使科学家能够评估积极或消极气候变化反馈的可能性。该项目支持的两名研究生将接受从遥感、地形建模到湿地甲烷排放生物地球化学等领域的培训。他们还将在该领域与一名美国研究者和一名乌干达合作者密切合作，第一手了解热带土壤、水文、植被和景观，以及如何在发展中国家开展研究。相反，一名年轻的乌干达科学家将有机会与美国科学家在一个具有当地和全球重要性的项目上合作。为了提高公众对dambo的认识，除了正常的科学出版物外，调查人员将指导一名本科生研究员建立一个dambo网站，其中包括遥感图像、实地照片、地图、统计数据、参考书目和灰色文献。

Molecule for molecule, methane (CH4) is about 30 times more effective as a greenhouse gas than carbon dioxide (CO2) on a 100-year time scale. Natural wetlands are the largest single source of global methane emissions and are the only source that responds directly to climate change. Despite the methane's significance, large uncertainties surround estimates of global CH4 emissions from natural wetlands. Uncertainties are particularly large for tropical wetlands (accounting for the majority of wetland emissions) due to the paucity of ground observations, detailed maps, and data for most of the developing world. Dambos (seasonally saturated, channelless valley floors) constitute the largest geographic extent of seasonal wetlands in Central and Southern Africa, occupying up to 20 percent of the central African plateau with more than 200,000 km2 of total extent. The objective of this project is to construct a spatially and temporally explicit estimate of methane emissions from 2500 km2 of representative dambos in the northern Luwero District, Uganda. The investigators will use multispectral (ASTER) remote sensing combined with digital terrain modeling to stratify the landscape, distinguishing dambo wetlands from upland regions as well as soil and hydrologic variability within dambos. Representative sites will be selected for detailed soil and vegetation characterization, hydrologic and temperature monitoring, and the measurement of methane fluxes. The project team will monitor methane fluxes through one major wet season and hydrology over one and a half years or three wet seasons. Using this data, they will identify key controls on dambo methane fluxes, and construct an empirical model relating these fluxes to soil properties, vegetation, temperature, and hydrology.This project will provide the first rigorous quantification of methane emissions from dambos, providing the basis for a first-order estimate of methane emissions over annual and seasonal for tropical dambo wetlands throughout Central and Southern Africa. Theses data will help constrain highly uncertain tropical source estimates for global atmospheric methane models. The modeling strategy employed "linking a profile-scale methane model to a dynamic landscape wetland model" supports predictions of the response of tropical dambo wetlands to future climate change scenarios, allowing scientists to assess the potential for positive or negative climate change feedbacks. The two graduate students supported on this project will be trained in fields ranging from remote sensing and terrain modeling to the biogeochemistry of wetland CH4 emissions. They will also work closely in the field with both a U.S.-based investigator and a Ugandan collaborator, learning first hand about tropical soils, hydrology, vegetation, and landscapes as well as how to conduct research in a developing country. Conversely, a young Ugandan scientist will have the opportunity to work with U.S. scientists on a project of both local and global importance. To raise general awareness of dambos, in addition to normal scientific publication the investigators will direct an undergraduate researcher to construct a dambo website with remotely sensed images, photos from the field, maps, statistics, a bibliography, and grey literature.