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

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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.