Murray State Theses and Dissertations

Abstract

There is high uncertainty in quantifying carbon (C) source-sink dynamics of freshwater mineral soil wetlands. While these wetlands store significant amounts of C in soils and trees, they also have a high potential to emit methane (CH4), specifically through tree stems. There is limited data on the spatial and temporal drivers of tree stem CH4 fluxes, especially in temperate forested wetlands. In this study, we measured CH4 fluxes from the stems of bottomland hardwood tree species (Taxodium distichum, Acer rubrum, Liquidambar styraciflua, Quercus pagoda, and Quercus stellata) across a year (i.e., measured ~ per season) and topographic settings (i.e., a pond edge, reservoir edge, floodplain, and terrace) to capture spatial and temporal variation in flux rates. Averaging across all CH4 flux measurements, tree stems had a mean efflux of 7.30 ± 40.80 (SD) nmol CH4 m-2 sec-1 and soils had a mean efflux of 1.18 ± 13.16 nmol CH4 m-2 sec-1. Seasonal patterns appeared to covary with high water tables and high subsurface temperatures. For example, the reservoir edge, driven primarily by surface water, had peak fluxes on stems in summer during high water and high temperatures and was low during the rest of the year. T. distichum was the only species that showed a direct effect of height on the stem and CH4 fluxes, with higher effluxes lower on the stems. However, across all stems we found that the magnitude of the difference between fluxes taken at lower and upper positions on the stem increased with mean CH4 tree stem efflux. T. distichum at the pond edge also had an exponential decay relationship between efflux and diametric stem size, which was present across the annual cycle. In summation, the strongest relationships were found in T. distichum at the pond edge, which also releases magnitudes more CH4 than floodplain and terrace systems. We note, that while we failed to capture summer flooding events in these latter systems that could promote higher CH4 efflux, our sampling captured the most common environmental conditions these systems experience. We suggest future research efforts focus on capturing those extremes and increasing spatial and temporal sampling in the higher emitting systems.

Year manuscript completed

2025

Year degree awarded

2025

Author's Keywords

carbon, stem, flux, wetland, hydrology, bald cypress

Degree Awarded

Master of Science

Department

Biology

College/School

Jesse D. Jones College of Science, Engineering and Technology

Thesis Advisor

Jessica B. Moon

Committee Chair

Jessica B. Moon

Committee Member

Michael B. Flinn

Committee Member

Gary E. Stinchcomb

Committee Member

Kate He

Document Type

Thesis - Murray State Access only

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Available for download on Saturday, September 25, 2027

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