Research on groundwater flow systems using the concentration of anions

利用阴离子浓度对地下水流动系统进行了研究。研究领域有四个方面；草木木克山、古森市周边河流扇、芦原原河流扇、筑波山。草木木克山斜坡下部有HCO^<3->和SiO_2的高浓度区，认为该地区地下水停留时间较大。NO^<3->浓度是肥料污染的一个指标，从土地利用图对比来看，受污染的水体主要分布在农田或牧场，而不是水田。在高森地区，通过水质测绘估算了Hayatuki河补给地下水的水系线，这些水系线与地质构造推算的水系线相吻合。从芦原原的观测结果来看，浅层地下水受到家畜粪便的污染，并且污染物（如NO^<3->）沿地下水的同一路线流动。在筑波山坡面对基流进行了采样和分析。水质空间变化明显，东部山区样品浓度低，西部山区样品浓度高。这些差异是由岩石风化的不同造成的。从野外观测结果看，地下水水质存在着显著的空间变化，尤其是阴离子浓度。这些空间差异有助于估计地下水流动模式或系统。作者将对沿线下游的水质，特别是阴离子的变化进行规划研究。

The studies on groundwater flow system by using the concentrations of anion were carried out. The fields of studies are four areas ; Mt.Yatsugatake, the fluvial fan around the city of Gosen, the fluvial fan in the Nasunogahara, and Mt.Tsukuba.On the mountain slope of Mt.Yatsugatake, the high concentration area of HCO^<3-> and SiO_2 are found at the lower part of the slope, and groundwater in this area is considered that the residence time is large. The concentration of NO^<3-> is an indicator of pollution by fertilizer, and from the comparison of land use map, the polluted water is distributed in the area of farm or pasture, not paddy field.In the Gosen area, the stream lines of groundwater recharged by the Hayatuki River were estimated by the mapping of water qualities, and the lines are coincide with the lines extimated from the geological structure.From the results of the observations in the Nasunogahara, the shallow groundwater is polluted by the excrement of domestic animals, and the pollutant, for example NO^<3->, flows on the same route of the groundwater.On the slope of Mt.Tsukuba, the base flow were sampled and analyzed. The water quality changes remarkably in space, i.e., the concentration of samples of eastern part of the mountains are low and those of western part are high. These differences were caused by the differences of the weathering of rocks.From the results of field observations, there are some remarkable spatial changes in water quality of groundwater, especially in the concentration of anion. These spatial differences are useful to estimate the groundwater flow patterns or systems.The author will make plan for the study on the changes in water quality, especially in anion, to the downstream along the stream line.