Methane dynamics in agricultural cropping systems and near source wastewater treatment lagoon and process evaluation of incubation method for methane oxidation

Abstract

The three chapters included in this dissertation center on the dynamics of soil methane fluxes and the potential of soil as a methane sink. Soil CH₄ consumption is a natural CH₄ mitigation strategy, and understanding how it works can aid in the development of strategies to reduce CH₄ emissions from soil and support soil health. The first study quantified CH₄ fluxes at the soil surface interface near a dairy lagoon, which served as the CH₄ point source. Methane gas samples were collected using a close vented gas chamber, injected into pre-vacuumed vials, and quantified for CH₄ concentration using gas chromatograph. Net CH₄ influx were greater in chambers that were installed closest to the lagoon than in chambers further away from the lagoon. The second study evaluated a process of incubation method that uses headspace analysis of incubation chambers of CH₄ concentrations quantified by gas chromatograph (GC) using soil soils from different land management. The first phase of incubation created conditions that exposed the microbes to high levels of CH₄ and may have increased the microbes’ methanotrophic potential. The derived calibration curve generated through known concentration of standard CH₄ gas can be used as a simple and practical tool in quantifying and estimating concentrations of CH₄ during the CH₄ oxidation process in a laboratory setting. The last study utilized a large data set of CH₄ that was a result of studies conducted to assess N₂O emissions. The different field experiments generated 11,837 individual measurements that were taken in 362 sampling events of which only 21% or 2,082 manifested a significant methane flux. Methane consumption is a frequent result of the CH₄ dynamics between the atmosphere and soil. The flux average value was -0.0016 mg CH₄-C m⁻² hr⁻¹ and if this flux rate accurately represents the average consumption of CH₄-C in cropland soils of the Central Great Southern Plains, it would remove 55,950.40 Metric tons CO₂ eq yr⁻¹ from the 8.8 million acres of cropland in Kansas.