Estimating Emissions of Ammonia and Methane from an Anaerobic Livestock Lagoon Using Micrometeorological Methods and Inverse Modeling

Evaluating the impact of increased carbon and nitrogen emissions on local air quality and regional bionetworks due to animal agricultural activity is of great interest to the public, political, economic and ecological welfare of areas within the scope of these practices. Globally, livestock operations account for 64% of annual anthropogenic emissions of ammonia (NH₃) ^[1]. Concerning methane (CH₄), anaerobic lagoons from commercial dairy operations contribute the second largest share of CH₄ emissions from manure in the United States^[1], and additionally are a local source of NH₃ as well. Anaerobic lagoons are commonly used in commercial animal agriculture and as significant local sources of greenhouse gases (GHG), there is a strong need to quantify GHG emissions from these systems. In 2012 at a commercial dairy operation in Northern Colorado, USA, measurements of CH₄ were made using eddy covariance (EC), while NH₃ was estimated using a combination of real-time monitoring (cavity ring-down spectroscopy as well as time-integrated passive samplers). Methane emissions have been measured at this lagoon using EC since 2011, with fluxes ranging from 0.5 mg m^-2 s^-1 in early summer to >2 mg m^-2 s^-1 in late summer and early fall. Concentration data of both CH₄ and NH₃ were used to estimate emissions using a 2-dimensional inverse model based on solving the advection-diffusion equation^[2]. In the case of the CH₄-EC data, results from the inverse model were compared with the EC-derived flux estimates for enhanced parameterization of surface geometry within the lagoon environment. The model was then applied using measured NH₃ concentrations to achieve emissions estimates. While NH₃ fluxes from the lagoon tend to be much lower than those of CH₄ by comparison, modeling emissions of NH₃ from the simple geometry of a lagoon will assist in applying the model to more complex surfaces. _{[1] FAO, 2006. Livestock's long shadow: Environmental issues and options. Livestock, Environment, and Development Initiative. Food and Agriculture Organization of the United Nations, Rome, Italy. [2] Loubet, B., Génermont, S., Ferrara, R., Bedos, C., Decuq, C., Personne, E., Fanucci, O., Durand, B., Rana, G., Cellier, P., 2010. An inverse model to estimate ammonia emissions from fields. Eur. J. Soil Sci. 61: 793-805.} Panorama of a weather station (left) utilizing micrometeorological methods to aid in estimating emissions of methane and ammonia from an anaerobic livestock lagoon (center) at a commercial dairy in Northern Colorado, USA.