我国杭州地区秋季稻田的甲烷排放

METHANE EMISSION FROM A RICE PADDY IN HANGZHOU OF CHINA DURING GROWING SEASON OF LATE RICE

1987年秋季在杭州郊区采用一套全自动的观测系统,对稻田的甲烷排放进行了观测。在整个晚稻灌溉期内,稻田是大气甲烷的一个源地,其甲烷释放率最高可达240mg/m^2·h。甲烷释放率具有很强的季节性变化,在水稻成熟期之前,甲烷释放率一般在40-60mg·CH_4/m^2·h的水平上波动,在成熟期间则降为10mg·CH_4/m^2·h的水平。除移栽期外的整个水稻生长期间的甲烷平均释放率为39mg/m^2·h。甲烷释放率具有明显的日变化,一般在午夜至凌晨3—4点达最大值,白天较低,变化也较小。这可能与水稻植物体由于其生理上的日变化引起的甲烷气体传输能力的日变化有关。实验没有观测到不同施肥(K_2SO_4和菜饼)对甲烷释放率的明显影响。阴雨天的降温一般在2—3天后引起甲烷释放率的迅速下降,这可能是因土壤中发酵细菌如产甲烷菌数量的减少造成的。尽管甲烷释放率和土壤温度在整个生长期间基本上是逐步下降的,但两者之间并没有简单的正相关性。土壤中产生的甲烷气体只有一小部分释放到大气中,从土壤中冒出来的气泡往往可引起释放率的急剧上升。1985年全球稻田的甲烷释放量估计为134±3lTg(1Tg=10^(12)g),其中12±26Tg和30±6Tg分别来自亚太地区和中国稻田。

Methane release rates from a rice paddy were measured in the suburbs of Hangzhou / China by using an automatic and continuous measuring system in 1987 during a almost complete growing season of late rice. The rice paddy was a source of atmospheric methane with maximum CH4 release rates up to 240 mg.CH4/ m2· h during the time of flooding. A seasonal variation with high flux rate in the order of 40-60 mg · CH4/ m2 · h before ripening and the low flux rates of 10mg · CH4/ m2 · h during the ripening stage was observed. Over the growing period, except transplanting stage, the averaged CH4 release rate is 39 mg · CH4 / m2 · h. The release rates showed strong diurnal variation with highest values being at midnight or at very early morning and much lower values at the daytime which is possibly related to the diurnal variation of CH4 gas transporting ability caused by rice plants. Significant differences of the CH4 release rates between the unfertilized field plots and the plots with chemical (K2SO4) fertilizer and with organic (rapeseed cakes) fertilizers were not observed. The decreasing temperature in overcast and rainy days generally caused rapid decreasing of CH4 release rates in 2-3 days, it is probably due to the decrease of the amount of methanogenic bacteria inside the soil. There is no simple correlation between the CH4 release rates and the soil temperatures, although both of them declined in the whole growing season. Only a small part of the CH4 gas produced inside the soil released into the atmosphere, and gas bubbles emitted occasionally from the soil could cause steep rise in CH4 release rates.The global annual CH4 emission from rice paddies was estimated to be in the order of 100-160 Tg (Tg = 10g) for 1985, 92-142 Tg and 23-35 Tg of which were from Asia and China, respectively.