Groundwater recharge and pollution management using environmental isotope

硝酸氮在日本地区地下水中被广泛检测，已成为许多发达国家面临的重大环境问题。地下水中的硝酸盐被认为主要来源于对耕地施肥的农业实践以及工业和生活污水的土地施用。该研究项目旨在揭示森林、耕地和城市化等土地利用对地下水化学特征的影响，并与地方政府的几个环境研究所合作。通过对区域地下水中硝酸盐氮和其他化学物质的分析，计算了人类活动（如农业实践和土地利用污水等）对氮的负荷。为此，在山形县的一个耕地研究盆地中，建立了7口不同深度的地下水调查井。特别是硝酸盐δ（^<15…）的氮同位素值的测定，对区域地下水中硝酸盐的来源进行了判别。结果表明，硝态氮和SO4^<2->离子浓度随地下水深度的增加而降低，而氮同位素比值δ ^<15 >n增加。氮在地下环境中的这种变化表明浅层地下水明显受到无机肥施用及其渗滤液的影响。除山形盆地外，在冲绳县宫古岛的地下水中也测量到了δ ^<15>N的同位素值。三角洲^<15> N值随地下水流经耕地而略有降低，从7.28%降至5.76%，且城市地区比耕地地区高12%左右。氮同位素比值的变化为确定地下水中氮的来源和利用其他溶解化学物质计算氮负荷，分离单个氮源提供了可能。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