Spatial distribution of infiltration and solute transport through root zone and effect of preferential flow

在考虑优先流影响的情况下，考察了根系区入渗速率的空间分布及其对溶质运动的影响。2003年，观测并考察了1)树冠下雨水量的空间分布和2)降雨期间和降雨后表层土壤体积含水量的空间分布。对于1)，在树木周围的地面上制作约20个网格，观察树冠下的穿透物分布，考察树枝和叶子对穿透物分布的影响。结果表明：在阔叶树中，穿透物的空间分布是冠层投影面积率、离茎距离和降雨量的函数。对于2)，在树木周围的地面上制作24格目，使用研究费用购买的TDR水分计在降雨后立即观测表层土壤的体积含水量。结果表明，在同一地区，含水量与其变化率之间的关系也不是恒定的。2004年，我们尝试用一个模型来解释2003年2)的结果，并对森林坡地的入渗、径流和溶质运动进行了研究。结果表明，低含水率下的入渗速率可以用水头梯度=1的模型来解释，但由于宏观孔隙优先流动，降雨后立即高含水率的假设不能解释入渗速率。此外，对于森林坡面，降雨后树木附近表层土壤的水分减少较小，SiO_2可以用来估计优先流的影响。

The spatial distribution of the infiltration rate and its influence on the solute movement was examined for the root zone with consideration about the influence of preferential flow In 2003, 1)the spatial distribution of rain water volume under a tree canopy and 2)the spatial distribution of volumetric water content of surface soil layer during and immediately after rainfall was observed and examined. For 1), about 20 meshes were made on the ground surrounding a tree, and the throughfall under tree canopy was observed and the influence of the branch and the leaf on throughfall distribution was examined. The results showed that the spatial distribution of the throughfall was expressed as a function of the projection area rate of canopy, the distance from the stem and amount of the rainfall for a broad-leaved tree. For 2),24 meshes were made on the ground surrounding a tree and the volumetric water content of surface soil layer was observed immediately after rainfall with the TDR moisture meter bought by the research expense. As a result, it was shown that the relation between the water content and its change rate was not constant also in the same place. In 2004, the result at 2) of the 2003 was tried to be explained by a model and the infiltration, runoff and solute movement in the forest slope were examined. The results showed that the infiltration rate could be explained by the model assuming hydraulic head gradient=1 for low water content, but it could not be explained by the assumption for high water content immediately after rainfall because of preferential flow through macro pores. Moreover, the results for forest slope showed that the moisture decrease of the surface soil after the rainfall was small near the tree and that the SiO_2 can be used for estimation of influence of preferential flow.