NSFDEB-NERC: Spatial and temporal tradeoffs in CO2 and CH4 emissions in tropical wetlands

湿地是一个碳悖论，具有巨大的碳储存能力，但也是甲烷（CH4）等碳的强大来源。世界各地的湿地对气候变化高度敏感，因为它们依赖雨水和地下水。饱和度的季节性变化有可能导致CO2和CH4形式的高度动态温室气体通量。热带湿地的研究尤其不足，但对全球CH4预算的贡献巨大。虽然巴西拥有广阔的湿地，但以前的工作主要集中在永久饱和的系统上，例如，亚马逊河或潘塔纳尔平原。相比之下，缺乏研究的塞拉多域包括永久性（泥炭地）和季节性淹没（季节性草原），湿地和干草原，饱和度随季节和周期性变化。气候变化有可能给这一地区带来更温暖和更干燥的条件，增加季节性和干旱草原的面积，同时可能增加温室气体排放。鉴于目前缺乏观测和预测这些关键的季节性系统的未来的重要性，这是至关重要的，以确定驱动温室气体排放和碳存储的空间和时间变化的饱和梯度，以及这些系统的空间范围随时间的变化机制。我们的总体目标是在巴西的研究中心克服这些知识差距。我们在塞拉多热带草原的实地和建模方法将集中回答三个问题：Q1。在饱和梯度上，海洋储存和通量的空间和时间异质性的驱动因素是什么？Q2.热带草原的饱和度（面积和周长）如何改变？季节和十年尺度？Q3.在未来的气候条件下，热带草原的海洋排放速率和形式将如何变化？为了测试Q1，空间分布的测量将与高时间分辨率的测量相结合，以了解整个饱和度梯度的温室气体，土壤和植被C动态。将使用静态通量室在空间上测量GHG变异性，并使用自动化室在时间上测量GHG变异性。随着时间的推移，将通过最初的土壤特性，结合植物物候，气孔导度，孔隙水化学，基线气候和地下水季节性的季节性测量来确定现场的变化。为了测试Q2，将结合高分辨率遥感和实地参考数据来绘制湿地范围，将使用季节性14C和210Pb测年来了解湿地范围在十年尺度上的变化。为了测试第三季度，第一季度和第二季度的数据将用于与PFLOTRAN反应性传输模型耦合的E3SM陆地模型的模拟。碳固存模式和温室气体排放量的估计将在空间上进行模拟，预测碳平衡的变化和温室气体与预期的变化，在区域气候和水文。

Wetlands are a C paradox, with huge capacity for C storage but also a strong source of C as methane (CH4). Wetlands worldwide are highly sensitive to climate change, given dependencies on rain and groundwater. Seasonal shifts in saturation have potential to lead to highly dynamic greenhouse gas (GHG) fluxes, in the form of CO2 and CH4. Tropical wetlands are particularly understudied but make outsized contributions to the global CH4 budget. Though Brazil has vast wetlands, previous work largely focused on permanently saturated systems, e.g., Amazon or Pantanal floodplains. In contrast, the poorly studied Cerrado domain includes permanent (peatlands) and seasonally inundated (seasonal grasslands), wetlands and dry grasslands, with saturation shifting seasonally and episodically. Climate change is likely to bring warmer and drier conditions to this region, increasing areas of seasonal and dry grasslands and concomitant potential increases in GHG emissions. Given current paucity of observations and importance of predicting future of these critical seasonal systems, it is vital to determine mechanisms driving spatial and temporal shifts in GHG emissions and C storage across the saturation gradient, as well as changes in spatial extent of these systems through time. Our overall objective is to overcome these knowledge gaps in sites in Brazil. Our combined field and modeling approaches in Cerrado tropical grasslands will focus on answering three questions: Q1. What are the drivers of spatial and temporal heterogeneity in sea storage and flux across saturation gradients? Q2. How does saturation extents (areas and perimeters) in tropical grasslands change over box? Seasonal and decadal scales? Q3. How will rates and forms of sea emissions from tropical grasslands change under future climates? To test Q1, spatially distributed measurements will be coupled with high-temporal resolution measurements to understand GHG, soil and vegetation C dynamics across the saturation gradient. GHG variability will be measured spatially with static flux chambers and temporally with automated chambers. Site changes through time will be determined by initial soil characterization, combined with seasonal measurements of plant phenology, stomatal conductance, porewater chemistry, baseline climate and groundwater seasonally. To test Q2, high resolution remote sensing and field reference data will be combined to map wetland extent, seasonally 14C and 210Pb dating will be used to understand wetlands extent changes at decadal scales. To test Q3, data from Q1 and Q2 will be utilized in simulations with E3SM Land Models coupled to PFLOTRAN reactive transport models. Estimates of C sequestration patterns and GHG emissions will be spatially simulated with projections of C balance changes and GHG with expected shifts in regional climate and hydrology.