Editor's Notes

Skylar Ross was recipient of an ORCA Travel Grant to present this research at American Geophysical Union Fall Meeting 2023.


Bald Cypress “Knees” Contribute to Methane Emissions in a Bottomland Hardwood Wetland

Skylar Ross1, Niklas Klauss1, Marissa Miles1, Bassil El Masri1, Jessica Moon1, Kabiraj Khatiwada2, Benjamin Runkle2, Gary Stinchcomb3

1 Murray State University, Murray, KY;

2 University of Arkansas, Fayetteville, AR; and

3 University of Memphis, Memphis, TN

Project Abstract:

Relatively little is known about carbon source-sink dynamics in bottomland hardwood wetlands. Identifying carbon pathways and their dominant controlling factors within these systems is critical. Bald cypress (Taxodium distichum) is a dominant tree species of southeastern United States wetlands. These trees can develop exposed woody root structures known as “knees,” which have been shown to contribute to wetland methane (CH4) emissions. However, there are significant variations in estimates of knee contribution to total ecosystem flux. We are measuring variation in CH4 fluxes from Bald cypress knees, soils, and 1 m2 plots containing both soils and knees as a function of microtopographic and climatic (i.e., drought and flooding) differences. During moderate-severe drought conditions in the Fall of 2022, knees acted as a source of CH4 even while surrounding soils acted as a sink. During more moderate drought conditions, in the Fall of 2023, we saw an increase in CH4 emissions from individual knees, but only from those located at a lower elevation. A historic rainfall event (dropping 17.7 cm of precipitation in 24 hours) in July 2023 also resulted in an ~ 250 % increase of CH4 emissions from knees at the lower elevation. The flooding and drought period data suggest fluxes are partially related to hydrologic factors. Sampling is ongoing to better understand the relationships between knee fluxes and surrounding environmental factors (i.e., hydrology, air and soil temperature, soil biogeochemistry, etc). Results from this study could allow for more accurate wetland ecosystem carbon modeling, which currently do not account for knee fluxes.



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