枣树冠层改变降雨截留历时过程同位素和化学特征

基于冠层截留历时过程降雨同位素和化学特征的研究很少,但却有助于揭示冠层截留特征及其对降雨同位素和化学特征的影响,于2016年9月17-18日和10月22-23日对黄土高原丘陵沟壑区的2场降雨事件林外降雨、穿透降雨和树干茎流历时过程进行连续采样及室内分析,研究降雨过程中矮化枣树冠层截留对降雨同位素和化学成分的改变、2016年7-10月4棵矮化枣树树干茎流以及林外降雨取样测定,分析矮化枣树形态特征对其树干茎流率的影响。结果表明:(1)矮化枣树树干茎流率可达2.3%~5.6%,2场降雨事件中当降雨量分别达到1.4,1.2mm时,开始产生树干茎流;(2)通过比较2场降雨事件历时过程穿透降雨、树干茎流同林外降雨的稳定同位素和水化学特征算术平均值得出,穿透降雨、树干茎流δ~2 H分别富集1.6‰~4.0‰和6.6‰~8.9‰,Cl~-浓度分别增加到林外降雨1.4~3.0倍和13.3~13.4倍,SO_4~(2-)浓度分别增加到1.5~2.7倍和4.8~7.1倍,穿透降雨和树干茎流相对林外降雨呈现一定滞后;降雨历时过程中稳定同位素δ~2 H与前时刻降雨以及截留过程进一步蒸发有关,水化学成分改变受植被截留影响逐渐减弱。

Canopy Interception Modified Intra-rainfall Isotopic and Hydrochemical Characteristics of Dwarfed Jujube Tree

Numerous studies have been conducted on canopy interception and its influence on inter-rainfall isotopic composition and hydrochemical properties.However,little is known about how isotopic and hydrochemical characteristics chage in rainfall duration.The objective of this study was to understand the isotopic and hydrochemical characteristics of dwarfed jujube tree in rainfall duration.The water from stemflow,throughfall and rainfall in an open air were sampled continuously from two intra-rainfall events on Sept.17-18 and Oct.22-23,2016 in the hilly and gully region of the Loess Plateau.At the same time,the volume of stemflow and rainfall in the open air were measured for four dwarfed jujubes of inter-rainfall events from July to Otc,2016.The results showed that:(1) Average stemflow rate of dwarfed jujube was 2.3％～5.6％ for inter-rainfall events;and stemflow was occurred when the rainfall amount reached 1.2 mm and 1.4mm during the two intra-rainfall evevts.(2) Relative to the rainfalls in the open area for two intra-rainfall events,the arithmetic-averaged δ2 H of the throughfall and stemflow were enriched by 1.6‰ ～ 4.0‰ and 6.6‰ ～ 8.9‰,respectively;their arithmetic-averaged Cl-concentrations increased by 1.4～3.0 times and 13.3～ 13.4 times,respectively;their arithmetic-averaged SO42-concentrations increased by 1.5～2.7 times and 4.8～7.1 times,respectively.The throughfall and stemflow lagged behind the rainfall in the open area;during the intra-rainfall events,the delay was influenced by jujube tree canopy interception,the isotope was influenced by the prior period rainfall and further evaporation.The changes of hydrochemical components were gradually weakened with the increasing elapsed time since the start of a rainfall event.