漓江上游典型植被蓄水-释放机理及水文响应

The relationship between forest and water resources has been a main problem in forest hydrology studies, which is also an important content for hydrological prediction and regulation. Lijiang River was a core mountain-water scenic spot in Guilin. Precipitation in Lijiang river basin was abundant, but its distribution of the year was irregular and rainfall mainly happened in rainy season. Our previous studies showed that the forest in upper reaches of Lijiang River had high water-holding capability and the time delay effect of flood peak was obvious. The key approach for solving the problem of water shortage is to enhance the regulation of water storage-release in forest vegetation. Using "Black box-Water balance" theory, an investigation on water distribution among canopy, litter and different soil layers in four typical vegetation will be conducted in this project, in which we focus on the mechanism of water storage during the rainfall and water release after the rainfall; We planed to simulate water storage-release processes along precipitation gradient and time sequence, determine the main impact environmental factors, discover the relationships between water storage-release processes and response of river runoff, and put forward valuable forestry management strategy. This research may help us better understand the mechanism of forest reservoir on regulating runoff and reduce the flood peak, alleviate the contradiction of water shortage in dry season, and then find an effective approach for the sustainable development of tourism in Guilin.

探究森林植被与水文过程的相互关系，加强水文预测与水文调控，是森林水文学的重要研究内容。水是漓江山水景观的"灵魂"，但漓江是"雨源补给型"河流，丰、枯水季节径流相差悬殊。根据前期研究，漓江上游森林植被蓄水能力强，能有效迟滞洪峰，缓解旱季缺水的关键在于蓄水的释放调配。为此，本项目拟以漓江上游4种典型森林植被为研究对象，利用"黑箱-水量平衡原理"，比较不同植被类型的林冠层、凋落物层和土壤层在降雨期间的蓄水过程，以及降雨后期蓄水的释放过程,分析不同降雨等级和时间序列下蓄水-释放过程规律，并进行回归模拟和时间序列分析；探寻影响蓄水-释放过程的主导因子；耦合蓄水-释放过程与河川径流水文响应，提出有利于提高森林植被蓄水和加快枯水期蓄水释放的经营设想。本研究对深入了解森林植被蓄水-释放机理，缓解漓江流域枯水期径流不足的矛盾，保护漓江这一珍贵旅游资源和促进地区经济的可持续发展，具有重要的理论和实践意义。

以漓江上游猫儿山林区的毛竹林、荷木林、杉木林和水青冈林4种典型森林植被为研究对象，对比森林植被叶面积空间分布以及其与地表凋落物之间的关系，比较不同层次土壤含水量及其影响因素，分析各层次土壤含水量对降雨的响应，河川径流发生过程与影响因素。结果表明：（1）杉木林叶分布的最大值在树冠顶部，从上到下叶面积指数逐渐下降；而木荷林从上层到下层叶面积指数呈增加的趋势；杉木林的冠层在水平空间分布的均匀性要好于其他2种林型，毛竹林分布均匀性最差。毛竹林土壤孔隙度大于木荷林和杉木林，但毛竹林的浅根性和速生性对表层土壤水含量影响更大；（2）大气降水是土壤含水量变化的主要因素，土壤含水量是降雨与植被垂直结构及蒸腾作用共同作用的结果。由于荷木林冠层结构复杂，与毛竹林和杉木林相比，荷木林蓄水能力更强；毛竹林、荷木林和杉木林三种植被垂直结构明显，导致土壤含水量垂直变化趋势不同；（3）从小雨到暴雨，土壤含水量对降雨的响应都可以分为平台期、上升期、峰值期和退水期；各层次土壤含水量对降雨的响应是比较复杂的。各层次土壤含水量与年降雨分配关系密切，随着雨旱两季变化，毛竹林、荷木林和杉木林不同层次土壤水分随降雨变化趋势基本一致。各层次土壤含水量对降雨的响应根据降雨等级发生变化。深层土壤对降雨的响应与产生饱和界面，地下水位抬高有关；（4）地表径流平均滞后时间为70 min。在连续降雨的情况下，降雨滞后效应不再明显，甚至出现地表径流与降雨同步的现象，小降雨可能产生大的地表径流，从而加大流域在雨季发生洪灾的风险。降雨后退水持续时间与前期降水及后期降水叠加有关。湿季径流系数略大于旱季，干季降水量减少，且森林植被消耗大量水分，减少了枯水期径流的产生，增大发生旱灾的风险。本研究为揭示漓江上游森林植被对降水产流的调节作用，客观评估漓江上游水资源潜力、加强流域水资源管理和森林经营提供科学依据。