Khokhar Nadar Hussain, Park Jae-Woo
Department of Civil and Environmental Engineering, Hanyang University, Haengdang-dong, Seongdong-gu, Seoul, 04763, South Korea.
Environ Monit Assess. 2017 Aug 24;189(9):468. doi: 10.1007/s10661-017-6184-z.
Manual closed chamber methods are widely used for CH measurement from rice paddies. Despite diurnal and seasonal variations in CH emissions, fixed sampling times, usually during the day, are used. Here, we monitored CH emission from rice paddies for one complete rice-growing season. Daytime CH emission increased from 0800 h, and maximal emission was observed at 1200 h. Daily averaged CH flux increased during plant growth or fertilizer application and decreased upon drainage of plants. CH measurement results were linearly interpolated and matched with the daily averaged CH emission calculated from the measured results. The time when daily averaged emission and the interpolated CH curve coincided during the daytime was largely invariant within each of the five distinctive periods. One-hourly sampling during each of these five periods was utilized to estimate the emission during each period, and we found that five one-hourly samples during the season accurately reflected the CH emission calculated based on all 136 hourly samples. This new sampling scheme is simple and more efficient than current sampling practices. Previously reported sampling schemes yielded estimates 9 to 32% higher than the measured CH emission, while our suggested scheme yielded an estimate that was only 5% different from that based on all 136-h samples. The sampling scheme proposed in this study can be used in rice paddy fields in Korea and extended worldwide to countries that use similar farming practices. This sampling scheme will help in producing more accurate global methane budget from rice paddy fields.
手动密闭箱法被广泛用于稻田甲烷（CH）测量。尽管CH排放存在昼夜和季节变化，但通常在白天采用固定的采样时间。在此，我们在一个完整的水稻种植季节监测了稻田的CH排放。白天CH排放从08:00开始增加，在12:00观测到最大排放。在植株生长或施肥期间，每日平均CH通量增加，而在植株排水后降低。CH测量结果进行线性插值，并与根据测量结果计算出的每日平均CH排放相匹配。在五个不同时期中的每个时期，白天每日平均排放与插值CH曲线重合的时间基本不变。利用这五个时期中每个时期的每小时采样来估算每个时期的排放，我们发现该季节的五个每小时样本准确反映了基于所有136个小时样本计算出的CH排放。这种新的采样方案简单且比当前的采样方法更高效。先前报道的采样方案得出的估算值比测量的CH排放高9%至32%，而我们建议的方案得出的估算值与基于所有136小时样本得出的估算值仅相差5%。本研究中提出的采样方案可用于韩国的稻田，并推广到全球采用类似耕作方式的国家。这种采样方案将有助于更准确地编制全球稻田甲烷收支。
