利用涡度相关技术研究了2013年7月至2014年6月浙江天目山常绿落叶阔叶混交林生态系统水汽通量变化特征,结合气象要素的观测,进一步分析了净辐射对水汽通量的影响。结果表明:浙江天目山常绿落叶阔叶混交林生态系统全年水汽通量基本为正值,各月水汽通量日变化趋势基本呈单峰型曲线,7月水汽通量峰值最大(0.115 g·m~(-2)·s~(-1)),1月最小(0.029 g·m~(-2)·s~(-1))。四季的水汽通量平均日变化中,峰值的大小为夏季>春季>秋季>冬季。生态系统全年蒸散量为721.25 mm, 在相近纬度的不同类型森林生态系统中处于较低水平,全年蒸散量占降雨量的51.46%,各月蒸散量均小于降雨量。生态系统全年净辐射为3 305.65 MJ·m~(-2)·a~(-1)。季节尺度上,对生态系统水汽通量与净辐射进行回归分析,显示四季的相关性都极显著。夏季相关系数(R~2)最大,为0.500,其次为春季(0.318),秋季(0.232),冬季最低(0.125)。
英文摘要:
Evapotranspiration (ET) is an important component of ecosystem water and energy balances, and subtropical evergreen and deciduous broadleaf forests play an important role in regional water cycles and budgets. To enhance prediction of climate change impact on the terrestrial ecosystem an improved understanding of the water and energy fluxes between vegetation and the atmosphere is needed. In Mount Tianmu area of Zhejiang Province, a subtropical evergreen and deciduous broadleaf mixed forest observation tower was set up in December 2012 with a three dimensional ultrasonic anemometer, a H2O/CO2 infrared analyzer, and conventional meteorological instruments for measuring a multi-layer gradient of temperature and humidity, windspeed, and radiation. Based on data observed from July 2013 to June 2014, water vapor flux features of the ecosystem were analyzed, and the net radiation responses to water vapor flux were determined. Results showed that annual water vapor flux was positive with distinct diurnal and seasonal variations. The maximum monthly water vapor flux occurred in July with a maximum daily 0.115 g·m~(-2)·s~(-1); the lowest was in January with a maximum of only 0.029 g·m~(-2)·s~(-1). The maximum quarterly water vapor flux occurred in summer, and the lowest was in January. The annual total ET was 721.25 mm (about 51.5% of the annual precipitation). The annual net radiation (Rn) for this ecosystem was 3 305.65 MJ·m~(-2). Also, Rn was the main driving force of ET and was a key factor in energy balance. Thus, water vapor flux being positive meant that the ecosystem was the source of water vapor.