城市公园绿地水、热与CO_2通量观测与分析

Analysis of water,heat and CO_2 fluxes on urban green space

水、热和CO2通量是评价城市绿地生态效益的重要指标。在北京海淀公园中部和边缘架设涡度相关系统,连续观测和定量研究城市公园绿地影响下的通量变化特征。结果表明,公园绿地所获得的净辐射在植被生长季节大部分用于植被的蒸散作用,潜热大于显热;而在植被非生长季节大部分用于显热,潜热数值非常小。晴天显热与潜热的比值在春季随着植被枝叶的生长逐渐减少,到夏季达到最小值约1/3,在秋季随着植被叶片枯黄逐渐变大,冬季达到数倍。公园绿地能量平衡率在52%～83%,普遍存在能量不平衡。公园中部的潜热观测值大于公园边缘,而显热小于公园边缘;公园中部CO2通量日均值为负,公园绿地是CO2汇。公园绿地在植被生长季节具有明显的降温增湿、吸收CO2等生态效应。

Urban green spaces largely affect energy and mass exchange in urban ecosystem, and they can decrease temperature, increase humidity, absorb carbon dioxide and release oxygen. It is significant to quantitatively evaluate the impact of urban green space on urban environment. Base on the surface energy and CO2flux measurements in Haidian Park, Beijing, the water, heat and CO2 exchange was analyzed in this paper. The results show that most of incident solar radiation is changed into latent heat flux （LE） during growing season, while it is mainly changed into sensible heat flux（H） during non-growing season. The ratio of H and LE decreases from spring to summer, with one-thirds in summer and several times in winter. LE is greater in the central park than that on the fringe of the park. The most important environmental factors controlling LE are net radiation, relative humidity and atmospheric temperature. The energy imbalance phenomenon is found in this study, with energy balance ratio ranging from 52% to 83%. It is also showed that the diurnal average of CO2flux is negative. Urban green space is the sink of carbon dioxide during growing season.