降水对鼎湖山季风常绿阔叶林土壤水氘特征的影响

Effects of Precipitation on Characteristics of Deuterium Isotope in Soil Water in a Monsoon Evergreen Broad-Leaved Forest in Dinghushan National Nature Reserve

【目的】分析我国南亚热带鼎湖山季风常绿阔叶林土壤水的水分来源、不同强度降水在土壤剖面中的时空运移过程及对各层土壤水的贡献率,为研究降水格局变化下鼎湖山自然保护区森林生态系统水循环过程及区域水资源科学管理等提供科学依据。【方法】利用氘同位素技术,比较不同降水条件下鼎湖山季风常绿阔叶林土壤水δD与潜在水源(大气降水、浅层地下水)δD,阐明土壤水的水分来源和降水在土壤剖面中的时空分布特征;运用二元线性混合模型计算不同强度降水对各层土壤水的贡献率。【结果】鼎湖山季风常绿阔叶林中土壤水δD介于大气降水δD和浅层地下水δD之间,土壤水主要来源于大气降水和浅层地下水;雨后5天内,小雨(9.8 mm)对0~10 cm表层土壤水贡献率最高(31.2%~44.6%),对10~40 cm深处土壤水贡献率次之(24.2%~32.0%),对40~80 cm深处土壤水贡献率较小(8.3%~15.7%),对80~100 cm深层土壤水贡献率最小(接近于0);雨后5天为中雨(20.0 mm)对0~10 cm表层土壤水贡献率最大(63.3%~78.9%),对10~40 cm深处土壤水贡献率次之(46.9%~74.0%),对40~80 cm深处土壤水贡献率较小(37.9%~63.0%),对80~100 cm深处土壤水贡献率最小(35.8%~47.5%);无论湿季还是干季,大雨(降水量>30 mm)后第1天,该次降水可渗透到80 cm以下深层土壤,且对80~100 cm深层土壤水的贡献率高达94.1%。【结论】0~10 cm表层土壤水δD与降水δD变化趋势一致,林中表层土壤水δD主要受降水δD的控制;降水强度越大,降水从土壤表层向深层土壤渗透速度越快,对80~100 cm深处土壤水δD影响越明显,降水对各层次土壤水的贡献率也越大;土壤剖面中土壤水δD的时空变化特征可指示降水在土壤剖面运移过程;无论小雨还是中雨,80 cm以下深层土壤水δD变化幅度较小,表明鼎湖山季风常绿阔叶林植被结构对降水在土壤剖面入渗过程具有显著的调控作用。

[ Objective] In order to provide scientific evidences for understanding the process of water cycle of forest ecosystem and managing regional water resources under the varying precipitation pattern in Dinghushan National Nature Reserve in the south subtropical zone of China. [ Method] In this study, the 8D of soil water and the potential water sources including precipitation and shallow underground water were analyzed to determine the source of soil water and the distribution of different intensity precipitation in the soil profile of the monsoon evergreen broad leaved forest in Dinghushan National Nature Reserve, using deuterium isotope technique. The contribution of precipitation in each layer of the soil profile was calculated by binary linear mixed model. [ Result ] The soil water 8D was found between those 8D values of precipitation and shallow underground water, indicating that precipitation and shallow underground water were the sources of soil water in the monsoon evergreen broad - leaved forest in Dinghushan National Nature Reserve. After a 5-day small rainfall （9.8 mm）, the contribution rate to surface soil layer （0 - 10 cm）was the highest （31.2% - 44.6% ） , followed by the layer ofl0 -40 cm （24.2% -32.0% ） and the soil layer of 40 -80 cm （8.3% - 15.7% ） , and the soil layer of 80 - 100 cm was the lowest, close to zero. With a moderate rainfall event of 20.0 mm, the contribution rate to surface soil （0 -10 cm） was the highest （63.3% -78.9% ） , followed by the soil layer of 10 - 40 cm （46.9% -74.0%） and the layer of 40-80 cm （37.9% -63.0%） , and the soil layer of 80-100 cmwasthe lowest （35.8% -47.5% ）. The precipitation infiltrated the deep soil （ 〉 80 cm） and the contribution to the soil layer of 80- 100 cm under heavy rainfall （ 〉 30 mm） was 94.1% during the same day either in the wet season or in the dry season. [ Conclusion] The results showed that 8D of surface soil water （0 -10 cm） was mainly controlled by rainfall δD. The faster the precipitation moving from the soil surface to the deep soil, the more obvious the effect of soil δD on the depth of 80 - 100 cm and the greater the rain contribution to the soil water at all levels with increasing the precipitation intensity. Deep soil water （80 -100 cm） δD value was basically kept stable under the small rainfall event of ≤20 mm. The results illustrated that vegetation structure of the monsoon evergreen broad - leaved forest in. Dinghushan National Nature Reserve played an significant role in regulation of the precipitation infiltration in the soil profile.