川滇高山栎灌丛冠层穿透水及其稳定同位素组成变化特征

Variations of Canopy Throughfall and Its Stable Isotopic Compositions in the Shrubland of Quercus Aquifolioides

植被冠层穿透水有重要的水文学和生态学意义,但目前的工作主要集中在森林植被,缺乏灌丛植被穿透水的报道;而灌丛植被在高山区的水文过程中具有重要作用。为此,在四川卧龙自然保护区3个川滇高山栎灌丛样地收集降水、穿透水和相应的气象资料,测定降水和穿透水的稳定同位素特征,分析各个样地穿透水量和穿透水率的变化,以及穿透水与降水稳定同位素值的差异及变化原因。结果表明穿透水量与降水量呈显著一元线性关系,穿透水率与降水量呈对数正相关。当降水量大于10mm/天时,样地B的穿透水有83.3%出现聚集效应,发生聚集效应时平均穿透水率为114.4%,样地C的穿透水有33.3%发生聚集效应,此时平均穿透水率为104.5%,但样地A没有出现聚集效应,表明在样地A冠层均一程度高。穿透水与降水稳定同位素组成没有显著差异,并有水量效应。但与降水稳定同位素值相比,穿透水稳定同位素值随着穿透水量的增大,先富集重同位素、再贫乏重同位素、最后趋向一致;这与林冠从干燥、蒸发显著,到湿润、出现饱和水汽界面,再到林冠下层形成的水滴占穿透水比重越来越小有关。

Canopy throughfall has important ecological and hydrological significances in the studies of water, energy and nutrient cycles in woodland ecosystems. Though shrub vegetation has significant functions in eco-hydrological processes of alpine and subalpine zones, reports about throughfall of shrub vegetation in these zones are few. We collected precipitation and canopy throughfall, and recorded meteorological data in the shrub land of Quercus aquifolioides in Wolong Nature Reserve from July 28 to September 6, 2003. Then we analyzed the relationships between the canopy throughfall and precipitation events, including the amount, the relative ratio, the isotopic characteristics and the isotopic differences. Results show that there is a significant unitary linear relationship between the amount of throughfall and precipitation. There also is a logarithmic positive correlation between the rate of throughfall and the that canopy of Plot A is homogeneous than that of Plot B and Plot C. When rainfall concentration occurred, the average rate of throughfall is 114.4% in Plot B and 104.5% in Plot C. The stable isotopic values of precipitation and throughfall has no significant difference. The regression line of stable hydrogen and oxygen isotopes in throughfall water is similar to that of precipitation water. Amount effect is also found in the stable isotopic values of through_fall, （e. g. precipitation water in Wolong during rainy and it is usually found in monsoon precipitation events seasons）. All of these isotopic characteristics indicated that the canopy has not obviously changed the conversion of precipitation to throughfall. Comparing with the stable isotopic values of precipitation, throughfall is enriched heavy isotopes when throughfall amount is about 2 mm. It mainly is caused by the evaporation in dry canopy. When throughfall amount is increased （e. g.4mm- 10mm）, the canopy would be wet, and then vapor from saturated water-vapor interface and dilute effect made more light isotopes into throughfall. As a result, throughfall is poor of heavy isotopes. Along with the increase of composition of precipitation and throughfall turned into throughfall. These variations of precipitation amount （e. g. more than 15 mm）, the isotopic is approached because more and more precipitation is directly isotopic differences show the interaction of shrub canopy and precipitation inputs.