Roles of capillary fringe to solute transport in subsurface water

土壤-水-地下水界面的毛细作用对溶质运移有重要作用，特别是在地下水位波动的情况下。本研究通过室内试验和野外观测，在地下水位变化较大的茨木县出岛地区，研究了土壤水分和溶质运移与土壤含水量、土壤在野外观测中，观测了地下水位、土壤含水量、水头、降雨量和水质。通过人工抽水诱发地下水波动，观测了地下水的水和溶质行为，主要结果如下：地下水的水和溶质行为随水位波动方式的变化而变化。这是快速下降似乎诱导不同的行为，从地下水位缓慢下降。地下水位的下降和上升会引起水和溶质的不同行为。威尔斯作为水的溶解行为具有滞后性，这可能来自于pF-含水量关系的滞后性。随着地下水位的位置和范围，不连续性地质的非均匀性，特别是层状土中的粉土或粘土，影响着水和溶质的行为，模拟研究将在两年多的实地观测后进行。

The capillary fringe between soil-water and groundwater zones might play an important roles in solute transport, especially under fluctuations of grounwater level.This research dealt with this subject through laboratory experiments and field observations in Dejima area of Ibaraki Prefecture, where groudwater levels change largely due to irrigation.In the laboratory experiments, relationships among water and solute transports, water content, and solute concentrations in small columns were analyzed.In the field observations, groundwater level, soil moisture, hydraulic head, rainfall, and water quality were measured. Fluctuations of groundwater were also induced artificially by pump-up and water and solute behaviors were observed.Some of observed results are as follows:Behaviors of water and solute vary after the manner of water table fluctuation. That is quick falldown seems to induce different behaviors from those of slow falldown of water table. Falldown and rising of water table could cause different behaviors of water and solute.Hysteresis of solution behaviors as wells as water is recognized, which seems to come from the hysteresis of pF-water content relationship.With positions and range of groundwater level, discontinuity (or non-homogeneity) of geology, especially silt or clay in layered soils affects behaviors of water and solute, and depth profiles of solute concentration.Simulation study will be done after field observations of two more years.