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

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.