Date of Award

Spring 6-8-2026

Document Type

Thesis (Undergraduate)

Department

Earth Sciences

First Advisor

Josh Landis

Second Advisor

Carl Renshaw

Abstract

Terrestrial Earth systems sequester an estimated 30% of annual anthropogenic CO2 emissions. The largest share is stored in global soils which collectively store more than 3 times the amount of carbon as the atmosphere. Floodplains and river systems, while covering only 5–8% of land area, store 20–30% of the global soil organic carbon (SOC), yet, the rate at which floodplains sequester carbon remains highly uncertain. Here I constrain floodplain carbon sequestration rates for a model northeastern river that has not been impacted by development or significant human activity. I calculate carbon stock using total organic carbon and derive carbon flux by age-dating soils with fallout radionuclides chronometry. Relative elevation above the channel is used as a conceptual model to understand the spatial heterogeneity of carbon stocks across the floodplain. Floodplain elevation has a positive correlation with carbon stock, but negative correlation with flux. Low-lying elevations having 10- and 30-year fluxes ~7 and ~15 times greater than forested soils. Looking at total carbon stock, however, forest soils contain ~2.2 times more carbon on average. I propose that this flux-stock relationship is driven by channel-floodplain exchange as characterized by frequency of flooding: carbon in the top 10 cm of soil has residence times of 2 - 10 years in low-lying elevations compared to 30 - 70 years in higher forest soils. This research is one of the first to measure carbon sequestration rates on northeastern floodplains, and provides insight into the use-cases of floodplain restoration and preservation as a mode of carbon sequestration.

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