METHANE EMISSIONS FROM ABOVEGROUND OPEN MANURE SLURRY TANKS

Estimates of methane (CH4) emissions from slurry tanks or lagoons in t he past have been made primarily by using chamber techniques, which ar e point specific and interfere with conditions at the slurry-atmospher e interface. This study is based on the use of sulphur hexafluoride (S F6) as a tracer gas to estimate CH4 transport from the slurry surface. The tracer was released from the surface of the swine slurry, and air samples were taken at the downwind rim of the tank over a 165 day per iod from June 12 to November 20, 1995, at the McGill University - Macd onald Campus Farm, Ste-Anne-de-Bellevue, Quebec, and analyzed for CH4 and SF6 concentrations (C). Knowing the SF6 source strength (Q), CH4 s ource strength was then determined from the measured downwind concentr ations using the C/Q ratio. Using this method, annual CH4 emission fro m the swine slurry tank was estimated at 56.5 kg CH4 m(-2) tank surfac e yr(-1) (+/- 20%). Assuming that diffusion processes at the nearby da iry tank were similar to those at the swine tank, the same C/Q ratio w as used to determine CH4 emissions from the dairy slurry based on down wind CH4, concentrations measured over the same period as at the swine tank. Annual methane emission from the dairy tank was estimated at 74 kg CH4 m(-2) tank surface yr(-1) (+/- 45%). On the basis of these est imates, CH4 emissions from outdoor holding tanks for swine and dairy s lurry in Canada were approximated at 0.71 Tg CH4 yr(-1) (+/- 40%) and 0.24 Tg CH4 yr(-1) (+/- 70%), respectively, giving a combined annual e mission of approximately 0.95 Tg yr(-1)(+/- 50%).