Measurement of Greenhouse Gases Emissions from a Suburban Dairy in Central California

Greenhouse gas emissions from societal activities are receiving increased attention around the world as governments and industries work to understand the intricacies of human-induced climate change and to develop strategies for mitigating human induced climate change through reductions in emissions of greenhouse gases. Regulatory strategies for controlling greenhouse gas emissions from various sectors of the economy are being developed. In the San Joaquin Valley, California, the greenhouse gas emissions from various agricultural operations are of principal interest. The focus of this study is on the data collected in the summer of 2014 as part of a larger effort to characterize greenhouse gases emissions from manure storage lagoons in suburban dairy in Central California. For three months, starting from the second week of July, data were collected around a target source, a 50 x 100 m manure lagoon, at a dairy on the campus of California State University that houses 275-300 Jersey and Holstein cows. Instruments used include those for direct measurement of ambient CH4 concentrations, such as TEI 55C (Thermo Scientific, Waltham, MA) methane analyzer and a commercial infrared laser spectrometer (GasFinder 2.0, Boreal Laser Inc.). The laser sensor is a portable, battery operated instrument with internal calibration, 1 ppmm sensitivity and a measurement frequency of 1 s. The sensor was set up about five meters downwind of the lagoon to give line-average concentration over a path length of 110m separating the laser and reflectors, which were both positioned on tripods at heights of between 1.5 m and 1.65 m. The air sampled by the CH4 analyzer was drawn through sampling tubes with inlets at locations that allow upwind and downwind measurement of CH4. The lagoon temperature was measured at three different levels corresponding to the surface, 2m and 8 m depths. A 3 m micrometeorological tower was located downwind of the lagoon and instrumented to measure CO2 concentration and flux, sensible and latent heat fluxes, wind speed and direction and air temperature. The results show a good agreement between the laser and downwind analyzer data and there was a significant difference between upwind and downwind measured CH4 concentrations, suggesting the lagoon as a CH4 source. No direct relationship was observed between the lagoon temperatures and CH4 concentration. There was an agreement between the CO2 and downwind CH4 concentrations. The CO2 flux showed both spatial and temporal variations with pattterns that are different from those observed in suburban environment. Linear regression revealed very weak trends between CH4 concentration and meteorological conditions, suggesting that although temperature certainly drives the chemical and biological activity that generates CH4, other conditions can have a large effect on these emissions, such as agitation of the surface and pumping.