Measuring methane fluxes from confined livestock operations using open-path eddy covariance: a challenging opportunity

Methane emissions from livestock operations are a significant component of the greenhouse gas inventory. However, quantifying CH4 emissions from enteric fermentation and manure management is plagued by uncertainty, due in part to the lack of good field measurements. The development of open-path CH4 gas analyzers with adequate resolution and time response has allowed more widespread use of eddy covariance – providing a new tool in the quest for improved inventories. Thus, research was conducted to measure CH4 fluxes from beef feedlots and dairies in Colorado, USA, using a LI-7700 open path analyzer (LI-COR, Lincoln, NE, USA). Initial work showed dust accumulation on the lower mirror strongly affected laser signal strength and a blow-off nozzle was designed to keep the mirror clean. Despite this improvement, data from cattle feedlots suggested results were influenced by movement of livestock within the source area and perhaps the episodic release of gas from the cattle (eructation; i.e., belching). Work at an anaerobic dairy lagoon also showed impacts of advection and episodic release of trapped CH4 in the source area. During some of these events, CH4 concentrations at 6 m exceeded 14 ppm for several hours even during sustained winds. While inferring fluxes from these results is challenging, data provide insights into the limits of the theory and instrumentation used to make eddy covariance measurements of CH4 under non-ideal conditions. This paper will examine these issues and solicit recommendations from the micro-meteorological community.