Greenhouse gas emissions from stored liquid swine manure in a cold climate

Current global warming has been linked to increases in greenhouse gas (GHG) concentrations. Animal manure is an important source of anthropogenic GHG, mostly of methane (CH4) and nitrous oxide (N2O). Country-specific emission estimates of these GHG can be obtained using IPCC 2000 guidelines, or suggested improvement, such as the USEPA approach for CH4 emissions, which is based on monthly air temperature (Tair). These approaches have not been validated against measured CH4 and N2O fluxes for liquid swine manure storage in cold climates due to the scarcity of year-round studies. A four-tower micrometeorological mass balance method was used at three swine farms (Arkell, Guelph, and Jarvis) in Ontario, Canada (annual Tair <10 °C), from July 2000 to May 2002. Methane and N2O concentrations were measured using two tunable diode laser trace gas analyzers, and manure temperature (Tman), redox potential (Eh) and composition were also measured. Dry matter content and Eh between sites and seasons varied from 0.6% to 3%, and −232 and −333 mV, respectively. Annual Tair was 8.4 °C, and Tman was on average 4 °C warmer. Mean N2O fluxes were not significantly different from zero, except for Jarvis with mean fluxes of 337.6 ng m−2 s−1 in summer and 101.8 ng m−2 s−1 in fall. Mean yearly N2O emission was estimated as 3.6 g head−1 yr−1, and was lower than the IPCC-based emission factor (EF) of 17 g head−1 yr−1. Our data suggests that N2O emissions from non-aerated liquid swine manure storage could be ignored in GHG inventories. Mean monthly CH4 fluxes obtained from half-hourly data varied between 4.6×10−3 and 1.05 mg m−2 s−1 (number of measurements per month=25–562). Measured CH4 emissions from May to October were mostly larger, and from January to April were lower than values predicted using the USEPA approach. Use of Tman improved monthly CH4 emission prediction using the USEPA approach compared to Tair with a lower limit of 7.5 °C (r2=0.64 vs. 0.355). The methane conversion factor derived from measured fluxes was 0.23, comparable to the USEPA derived values of 0.22–0.25, but much lower than the IPCC recommended value for cold climates (0.39).