Methane Dynamics of Vegetation-Soil Interactions in Bald Cypress and Other Bottomland Hardwood Forests

Methane (CH4) is one of the most important greenhouse gases and more than 30% of the total CH4 emissions originate from wetlands. There is high uncertainty in the contribution of mineral soil wetlands to global CH4 budgets and is estimated to be about 50% of the global wetland area. In this project, we are measuring the spatial and temporal dynamics of CH4 fluxes in soils and woody structures (stems and "knees") of temperate bottomland hardwood stands in Clarks River National Wildlife Refuge (CRNWR) in Western Kentucky, to improve land surface models. Soil collars and custom-built chambers were installed in 8 sites that span a hydrologic gradient from the terrace to the stream channel. Greenhouse gases were measured using a portable LICOR LI-7810 gas analyzer optical feedback-cavity enhanced absorption spectroscopy trace. The terrace sites are located within Cherry Bark Oak (Quercus pagoda) and Post Oak (Quercus stellata) stands. Measurements collected in July 2022 (two dates) showed that there are significant differences in soil CH4 (p-value = 0.026) fluxes across these stands; the Cherry Bark Oak stand was a larger soil CH4 sinks (-2.00 ± 0.62 nmol/m2/s) than the post oak site (CH4: -1.39 ± 0.11 nmol/m2/s). So far, we have not found a significant relationship between CH4 fluxes and soil moisture (p-value = 0.421) or temperature (p-value 0.225) on the terrace. However, micro-depressional pockets seem to allow for methane production that is more common in the lower elevation ecosystems. We will use our ongoing monitoring, to improve our understanding soil-vegetation interaction in hardwood bottomland wetlands and incorporate these functions into ongoing land surface modeling efforts