Earth and Planetary Sciences ETDs

Publication Date

Spring 5-16-2026

Abstract

Rivers transport sediment and carbon across Earth’s surface, and their floodplains can store carbon over decades to millennia, making them important to terrestrial carbon management. While soil carbon can persist long term, it may be released as greenhouse gases through processes like methanogenesis and heterotrophic respiration. Environmental controls on these fluxes remain poorly constrained across floodplains in different climate and geomorphic setting, but especially in semi-arid systems where measurements are limited. To address this gap, we quantified CO₂ and CH₄ fluxes along the Middle Rio Grande (New Mexico, USA) using 227 chamber measurements collected May to November 2025 at three floodplain sites. River discharge varied from 0.52 to 29.2 m³ s⁻¹ across this period. Channel margins maintained higher soil moisture (0.355 m³ m⁻³) than interior floodplain positions (0.097 m³ m⁻³), reflecting river stage versus precipitation controls. Mean CO₂ fluxes ranged from 3.02 to 3.84 µmol m⁻²s⁻¹, comparable to temperate systems. Negative CH4 fluxes in the floodplain interior indicate methane uptake, while positive CH4 fluxes in the low elevation channel margins indicate methane emission under saturated conditions. These results constrain carbon fluxes in semi-arid floodplains and improve representation of floodplain carbon cycling in regional and global carbon budgets.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Dr. Marisa Repasch

Second Committee Member

Dr. Alex Webster

Third Committee Member

Dr. Tobias Fischer

Language

English

Keywords

carbon cycle, Floodplains, Rio Grande, Greenhouse Gas, soil respiration

Document Type

Thesis

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