Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 11/6/1998
Publication Date: N/A
Technical Abstract: Methane emissions from enteric fermentation in ruminant animals are believed to be about 23% of all anthropogenic emissions of this gas. The estimates are based on extrapolations of "laboratory" experiments, largely chamber experiments, to the field scale. Verification with direct field measurements is needed. Gas production from sources within a test plot was calculated from measurements of the horizontal fluxes of the gas across upwind and downwind boundaries. The difference between the integrated horizontal fluxes on the downwind and upwind boundaries reflected animal emissions. Methane budgets were made for the test plot at 33- or 45-min intervals in experiments on cattle and sheep. Tests included calculation of recoveries from known gas releases, comparison with parallel measurements on discrete animals with a tracer technique, comparisons with a conventional micrometeorological approach, and with a backward dispersion model. The mass-balance method performed satisfactorily in all cases, but can suffer from errors arising from the large number of gas analyses required and the high precision necessary in the concentration measurement. It becomes unreliable because of gas density when there are light winds and with variable wind directions. It is, however, non-disturbing, has a simple theoretical basis, is independent of atmospheric stability or the shape of the wind profile, and is appropriate for flux measurements.