Does Sediment Storage Set the Pace of the Terrestrial Organic Carbon Cycle?

土壤中的碳含量大于大气中的二氧化碳含量。这意味着土壤碳储量的变化会影响气候。土壤碳也会影响农业土壤的肥力，并影响当地的水质。鉴于对人类和环境福祉的重大影响，本提案旨在加强对土壤碳储存的理解。研究将集中在河流的作用上，河流控制着土壤在被侵蚀之前留在景观上的时间，并通过洪水影响新土壤的形成。河流还可以影响土壤中的化学条件，从而影响土壤碳。工作将在一个只有火山岩的分水岭进行，以避免其他岩石类型中存在的“化石”碳。主要成果包括建立了一个新的土壤碳预测模型，培训了一名研究生和两名小学生物地球化学教师，以及编写了面向小学生的双语教材。稳定陆地有机碳（OC）的生物地球化学机制与土壤和沉积物储存在景观上的时间尺度相似（千年）。因此，利用储存过程的知识来全面了解陆地OC循环有可能改善预测并揭示新的动态，但需要新的数据和定量模型来验证和应用。这项工作旨在通过测试与土壤、沉积物和有机碳储存之间耦合有关的3个假设来解决这些具体的知识空白：(1) OC的年龄分布继承了河流作用对OC保存时间的调节；(2)OC保存过程通过河流对粒度分选和水文的控制影响OC保存的位点和生物地球化学机制；(3)冰川后景观演化通过增加景观土壤和沉积物的储存量增加了陆地OC库的大小。这些假设将通过遥感和调查估算沉积物储存、基于放射性核素的沉积物和OC储存时间测定，以及OC保存生物地球化学机制的元素、分子和同位素限制来评估。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The amount of carbon present in soils is larger than the amount of carbon dioxide in the atmosphere. This means changes in soil carbon storage can affect the climate. Soil carbon also affects the fertility of agricultural soil, and can influence local water quality. Given such significant implications on human and environmental wellbeing, this proposal seeks to enhance understanding of soil carbon storage. Research will focus on the role of rivers, which control the amount of time soil remains on landscapes before being eroded and which, through flooding, influence where new soil is formed. Rivers can also influence the chemical conditions in soil that affect soil carbon. Work will take place in a watershed containing only volcanic rocks to avoid the “fossil” carbon present in other rock types. Key outcomes include a new predictive model for soil carbon, the training of a graduate student and two elementary school teachers in biogeochemistry, and the development of bilingual educational materials for elementary school students. The biogeochemical mechanisms thought to stabilize terrestrial organic carbon (OC) all evolve over similar (millennial) timescales to the duration over which soil and sediment are stored on landscapes. Consequently, a holistic view of the terrestrial OC cycle that leverages knowledge of the storage processes has the potential improve predictions and reveal novel dynamics, but requires new data and quantitative models for validation and application. This work aims to address these specific knowledge gaps by testing 3 hypotheses related to the coupling between soil, sediment, and OC storage: (1) the age distribution of OC inherits its shape from the fluvial processes that regulate storage times, (2) storage processes influence the loci and biogeochemical mechanisms(s) of OC preservation via fluvial controls on grain size sorting and hydrology, and (3) post-glacial landscape evolution increases the size of the terrestrial OC reservoir via an increase in landscape soil and sediment storage. These hypotheses will be evaluated using estimates of sediment storage from remote-sensing and surveying, radionuclide-based determinations of sediment and OC storage times, as well as elemental, molecular, and isotopic constraints on the biogeochemical mechanisms of OC preservation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.