Eddy Covariance Measurements of Methane Flux from a Dairy Farm Lagoon

Livestock manure management in dairy operations is a known source of methane (CH₄), a potent greenhouse gas. Anaerobic waste lagoons are a common manure management technique; thus, their associated CH₄ emissions are relevant to national greenhouse gas inventories and local air quality. Our objective was to characterize the variability of summertime CH₄ emissions from a lagoon at a dairy facility in central Pennsylvania. Continuous flux measurements were taken over two weeks in July using the eddy covariance method, which uses high-frequency gas concentration and three-dimensional wind speed measurements to calculate turbulent fluxes from a source area. After data filtration based on turbulence characteristics and source area, the average CH₄ flux density from the lagoon was estimated to be 99 μmol m^-2 s^-1. This implies daily lagoon emissions of 881 kg CH₄, corresponding to an average emission rate of 340 g CH₄ per cow per day. We observed no apparent relationship between emissions and air temperature or relative humidity, though an extended measurement period is needed to better quantify the relationship that is expected to exist between air and/or slurry temperature and CH₄ flux. Our measured per-area emission rate is toward the high end of the range of estimates found in the literature. These results contribute to greenhouse gas inventory development and could have important implications for emission mitigation strategies.