沖縄県宮古島における地下水中の硝酸性窒素の窒素安定同位体比について [in Japanese] Nitrogen Isotope Ratio of Nitrate of Groundwater in Miyako Island, Okinawa Prefecture [in Japanese]
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To investigate nitrate sources in the aquifer consisting of unconsolidated limestone, stable isotope of nitrogen (δ<SUP>15</SUP>N) was measured in shallow groundwater from wells and springs under three land-use settings. The typical land-use settings and corresponding average nitrate concentrations and δ<SUP>15</SUP>N values were : residental areas,7.1mg/L and 8.0‰; agricultural areas,7.2mg/L and 5.2‰; and natural, undeveloped areas,5.3mg/L and 5.6‰, respectively. Average 15N values of urine sewages and commercial inorganic fertilizers were 18.10‰ and 0.5‰, respectively. Values of δ<SUP>15</SUP>N greater than 7‰ in residental areas suggest that nitrogen from sewages exists in groundwater. Values of δ<SUP>15</SUP>N less than 7‰ in agricultural areas and a part of natural, undeveloped areas suggest that nitrogen in groundwater was supplied by commercial inorganic fertilizers. Low nitrate concentarations and low values of δ<SUP>15</SUP>N in residental areas were caused by dilution with groundwater influenced by commercial fertilizers flowing into residental areas. High δ<SUP>15</SUP>N values in agricultural areas suggested that denitrification occurred actively.
- Journal of Groundwater Hydrology
Journal of Groundwater Hydrology 39(1), 1-15, 1997-02-25
Japanese Association of Groundwater Hydrology