三江源区退化高寒草甸蒸散的变化特征

为揭示三江源区退化高寒草甸水分收支变化特征,利用涡度相关和微气象方法对青海省果洛州大武镇退化高寒草甸生态系统的年蒸散变化进行了定量研究,并探讨了环境和生物因子对其影响。结果表明:年总蒸散量为481.9mm,年蒸散量约占年降水量的97%。生长季中日均蒸散量为2.3mm·d-1,而非生长季日均蒸散量仅为0.6mm·d-1。温度与蒸散量呈明显的指数关系;该区接收的太阳辐射较强,但净辐射占太阳辐射的比例相对较低(46%),在非冻土时期,蒸散量与净辐射呈线性关系;研究区降水量相对丰沛,与温度和净辐射相比,土壤含水量对蒸散的影响相对较小。本研究说明高寒草甸的退化加剧了生态系统的蒸散量,从而降低了生态系统涵养水分的能力,净辐射和温度是驱动三江源区退化高寒草甸生态系统蒸散最主要的环境因子。

Characteristics of Evapotranspiration of Degraded Alpine Meadow in the Three-River Source Region

To examine the characteristics of water budget of degraded alpine meadow in the Three-River Source Region (TRSR),we studied the annual variation of evapotranspiration (ET) and its controlling factors using the eddy covariance and micro-meteorological system in the Guoluo Prefecture,Dawu,Qinghai Province.The results showed that the annual amount of ET was 481.9 mm,and the ratio of annual ET to precipitation was about 97％.The average daily ET rate in the growing season was 2.3 mm · d-1,while the average daily ET rate in non-growing season was only 0.6 mm · d-1.There was a significant exponential correlation between ET and temperature.Solar radiation received by study site was strong,while the ratio of the net radiation to solar radiation (Rn/Rs) was relatively low (46％).ET was linear with the net radiation in non-frozen-soil period.Precipitation was relatively abundant in this alpine meadow,and the impact of soil water content on ET was relatively small in comparison with that of temperature and net radiation.This study suggested that the degradation of alpine meadow increased the ET,and thus reduced the water conservation capacity of ecosystem;net radiation and temperature were the most important environmental factors influencing ET for this degraded alpine meadow ecosystem in the TRSR.