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，研究了根区入渗速率的空间分布及其对溶质运移的影响。2003年，观测并研究了降雨过程中和降雨结束后，树冠下降雨量的空间分布和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设置约20个网格，观测树冠下的穿透雨，并研究分支和叶片对穿透雨分布的影响。结果表明，阔叶树穿透雨的空间分布是冠层投影面积率、距树干距离和降雨量的函数。试验2）在树木周围的地面上设置24个网格，用研究费用购买的TDR水分仪在降雨后立即观测表层土壤的体积含水量。结果表明，同一地点的含水量与其变化率之间的关系也不是恒定的。2004年，对2003年2）的结果进行了模型解释，并对森林坡面的入渗、径流和溶质运移进行了研究。结果表明，在低含水量条件下，入渗速率可以用水头梯度为1的模型来解释，而在降雨后立即出现的高含水量条件下，由于大孔隙的优先流，入渗速率不能用水头梯度为1的假设来解释。此外，对森林坡面的研究结果表明，降雨后树木附近表层土壤水分下降幅度较小，SiO2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.