Murray State Theses and Dissertations

Abstract

Aboveground woody root structures, such as bald cypress (Taxodium distichum) “knees”, may serve as a link for biogeochemical cycling across the soil-atmosphere interface. Knees have been shown to contribute to wetland methane (CH4) fluxes and models have predicted they might aid in developing soil nutrient “hot spots.” We investigated (Chapter I) spatial and temporal variation of CH4 fluxes from the surface of individual knees and controlling environmental factors, and (Chapter II) how the presence and density of knees may affect biogeochemical cycling through investigation of CH4 and carbon dioxide (CO2) fluxes from varying knee densities, and porewater chemistry near and away from knees across hydrogeomorphic positions. We found that knees are a net source of CH4 to the atmosphere. Water level and temperature explained 44 % of variation in CH4 fluxes across all sites, which was exemplified by decreased emissions during a severe drought and increased emissions following flooding events. Despite being CH4 sources, CH4 fluxes from soils and large quadrants containing soils and knees (“soil-knee”) were not significantly correlated with knee density. However, we observed significantly higher CO2 efflux and a non-significant trend of greater soil CH4 uptake near high knee densities during the fall of a severe drought (2022), which was not present the following fall during a moderate drought (2023), potentially due to more soil pore spaces near high densities which may have been filled with water during the moderate drought. We also found greater CO2 from high density soil-knee quadrants during the moderate drought, but not the severe drought. Porewater DOC concentrations were higher in a transect with knees compared to one without knees only at the site with the highest knee density and lowest fluvial energy. Porewater DOC was also positively correlated with water level, which may have been a confounding factor, and soil CH4 flux, which may indicate feedback of knees on CH4 fluxes. Our results show that knees are sources of CH4 that should be included in wetland CH4 budgets, and may also influence belowground nutrient cycling, but investigation into longer term stores (i.e., soil chemistry) may reveal greater insights.

Year manuscript completed

2025

Year degree awarded

2025

Degree Awarded

Master of Science

Department

Geosciences

College/School

Jesse D. Jones College of Science, Engineering and Technology

Thesis Advisor

Jessica B Moon

Thesis Co-Advisor

Bassil El Masri

Committee Member

Benjamin R Runkle

Committee Member

Gary E Stinchcomb

Committee Member

Michael Flinn

Document Type

Thesis - Murray State Access only

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Available for download on Sunday, August 01, 2027

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