基于动态箱法的北京延庆区牛粪堆放CH4和N2O排放量估算

畜禽粪便堆放管理会造成甲烷(CH_4)和氧化亚氮(N_2O)等温室气体的大量排放。通过联合国政府间气候变化专门委员会(IPCC)建议的排放系数等方法,可以实现对某一区域范围内畜禽粪便管理系统的温室气体排放总量的估算,但由于其排放受粪便管理、气候条件等因素的显著影响,直接套用IPCC的默认系数会产生较大的误差。为更加准确估算中国奶牛粪便管理所造成的CH_4、N_2O排放,该文在对北京延庆区奶牛生产与粪便管理模式进行了实地调研的基础上,采用动态箱法模拟了奶牛粪便不同季节短时自然堆放管理模式下的CH_4、N_2O排放过程,并对区域内的年温室气体排放总量进行了测算。研究结果表明,奶牛粪便在一个月的自然堆放管理模式下,每千克牛粪挥发性固体在春、夏、秋季的CH_4排放量分别为223.97、4 603.31、351.38 mg,每千克牛粪N_2O排放量分别为5.86、9.43、0.81 mg。2016年北京延庆区全年奶牛粪便CH_4、N_2O排放总量分别为13 342.50、347.87 kg。延庆区奶牛粪便堆放管理过程的CH_4排放因子为1.50kg/(头·a),小于IPCC指南中的1.78 kg/(头·a);受堆放时间较短的影响,N_2O的排放因子则显著小于IPCC的推荐值。若直接使用IPCC默认参数估算延庆区奶牛粪便堆放管理过程中的CH_4和N_2O排放量,会造成排放量的高估。

Estimation of annual CH4 and N2O emissions from solid dairy manure storage in Yanqing of Beijing based on dynamic chamber method

Abstract: Greenhouse gases, such as methane (CH4) and nitrous oxide (N2O) caused by manure storage inside the dairy farms are important contributors of global emissions to atmosphere, which is considered as the primary factor driving global warming. The Intergovernmental Panel on Climate Change (IPCC) guideline (Tier 2 for example) released in 2006 is treated as an authoritative method in estimating CH4 and N2O emissions from the animal manure management of a region, while its accuracy highly depends on the reliabilities of the parameters, including the CH4 and N2O emission factor (EF). While, different manure management modes and climatic conditions will lead to huge difference of the factors, and the estimation based on default factor of IPCC may result in a big deviation in the emissions from the manure management for a country or an area. Using the IPCC method, this paper simulated CH4 and N2O emissions from short-term stacked dairy manures in spring, summer and autumn by the dynamic chamber technique in the laboratory, and the annual emissions of CH4 and N2O from the manure management in Yanqing dairy farms was estimated based on the simulation results, as well as the field investigation on dairy management method and manure production. Finally, CH4 and N2O emission factor of the dairy manure management were calculated and compared with the defaults of IPCC. Results showed that CH4 emissions from the simulated dairy manure stockpiles were 223.97, 4 603.31 and 351.38 mg in spring, summer and autumn, respectively. The total CH4 emission of solid dairy manure management in Yanqing, Beijing was 13 342.50 kg in 2016, or 373.59 t CO2 equivalent. CH4 emission factor of solid manure storage from the simulation was 1.50 kg/(head·yr), which was statistically less than 1.78 kg/(head·yr) calculated from the default values of the relevant parameters in the IPCC guidelines. N2O emission from the simulated dairy manure stockpiles were 5.86, 9.43 and 0.81 mg/kg in spring, summer and autumn, respectively. Total N2O emission of solid dairy manure management in Yanqing, Beijing was 347.87 kg in 2016, or 92.19 t CO2 equivalent. N2O emission factor of solid manure storage from the simulation was 0.0004 kg/kg, which was significantly less than the defaulted value of 0.005 kg/kg in the IPCC guidelines. The difference on the emission factors could be partially explained by the storage period of collected manures from the barns and the open lots of dairy farms in Yanqing, Beijing, which was general less than 4 weeks, and quite differed from the circumstance that the default EFs of CH4 and N2O in IPCC guidelines. Thus, estimating the CH4 and N2O emissions from Yanqing area of Beijing with the default values of CH4 and N2O emission factors in the IPCC guidelines, the flux will be highly overestimated.