Groundwater recharge and pollution management using environmental isotope

硝酸盐氮在日本地区地下水中被广泛检出，已成为许多发达国家的重大环境问题。地下水中的硝酸盐主要来源于农业施肥和工业污水、生活污水的土地利用，本研究旨在揭示森林、耕地和城市化等土地利用方式对地下水化学特征的影响。通过对区域地下水中硝酸盐氮的分析，计算了农业生产、污水土地利用等人类活动引起的氮负荷。在山形县一个研究流域的耕地上，共布设了7口不同深度的地下水调查威尔斯井。特别是，硝酸盐的氮同位素值δ <15 关于我们 >N的测定，以判别区域地下水中硝酸盐的来源。结果表明，随着地下水埋深的增加，地下水中硝态氮和SO 4 ~（2+）浓度<2->逐渐降低，而氮同位素比值δ ~（2+）<15>N逐渐增加。氮在地下环境中的这种行为表明，浅层地下水明显受到无机肥料施用及其向地下水渗滤的影响。除山形盆地外，<15>还在冲绳县宫古岛的地下水中测定了δ ^ N同位素值。土地<15>利用类型的δ ^ N值表明，地下水通过耕地后，δ ^N值略有降低，例如从7.28%降低到5.76%，城市地区δ ^N值比耕地高，例如约12%。氮同位素比值的变化规律可用于地下水氮源的识别，以及利用其他溶解态化学物质计算氮负荷，分离单个氮源。少

The nitrate nitrogen was detected widely in the regional gound water of Japan, and has been becoming a great environmental issue in many developed nations. The nitrate in ground water is considered to originate mainly from agricultural practice of fertilizer application to arable land and land application of industrial and domestic sewage.The research program was designed to reveal the effect of land use like forest, arable land and urbanization on the groundwater chemical features in cooperation with several environmental institutes belonging to local governments. The nitrate nitrogen in regional groundwater was analyzed with other chemicals to calculate the nitrogen load from human activities such as the agricultural practice and land application of sewage etc. In order to do that, seven investigation wells to sample groundwaters at different depth were constructed in a study basin of arable land in Yamagata Prefecture. In particular, the nitrogen isotope values of nitrate delta ^<15 … More >N were measured for discriminating the origin of the nitrate discovered in regional groundwater. The results indicated that the concentrations of nitrate nitrogen and SO4^<2-> ion reduce with groundwater depth, while the nitrogen isotope ratio delta^<15>N increases. Such behavior of nitrogen in subsurface environment implies that the shallow groundwater is clearly affected by the inorganic fertilizer application and its leachate to groundwater. In addition to Yamagata basin, the isotope value delta ^<15>N was also measured in the groundwater of Miyakojima Isle in Okinawa Prefecture. The delta^<15> N values classified into the land use showed that they tends to slightly reduce with groundwater passing through arable land, for example, from 7.28 to 5.76 % and that they take higher values in urban area such as about 12% than those in arable land. The behavior of nitrogen isotope ratio has a possibility to identify the origin of nitrogen in groundwater and to calculate nitrogen load with use of other dissolved chemicals, separating individual nitrogen source. Less