| 环境氮同位素方法示踪石家庄市地下水中硝酸盐来源 |
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| 关键词:nitrate 15N/14N ratios of ground water Shijiazhuang city |
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| 15N/14N Ratios of Ground Water Nitrate in Shijiazhuang City |
| Grondwaters containing highconcentrations of nitrate characteristically occur in shallow water-table aquifers beneath areas of extensive human development, cultivation, live-stock, or septectands. High nitrate concentrations in Shijiazhuang groundwater are found in shallow aquifers. Groundwater concenerations from eighteen wells range from 8 to 94 mg/1 with 44% of the samples having nitrate concentrations higher than 45 mg/1. The level and extent of mitrate contamination appears to be in certain areas of Shijiazhuang necessitating identification of nitrate sources.
Cultivation induced mineralization of soil nitrogen, fertilizer, and animal or sewage wastes are the three main sources of nitrate pollution in groundwater. In many cases these sources pro-duce nitrate with distinguishable 15N/14N ratios, and on this basic isotopic data for nitrater have been successfully used for indentifying the source of pollution in a wide variety of groundwater environments.
Eighteen Samples erer collected in Shijiazhuang city for isotopic analyses. The samples came from the ater table aquifer, whrer overlying land use patterns range from the highly ur-baniaed sewered or septic tank areas to rural agricultural areas. The δ15N values for groundwa-ter nitrate range from +4.0‰- +17.7‰. Except two samples, theδ15N values for fifteen samples range from +4.0‰- +9.6‰ with an average of +6.7‰. It is heavier than would be expected if the nitrate were derived solely form nitrogen fertilizer (-4.0‰- +4.0‰).Groundwater nitrate does not result form direct leaching of nitrater ferfilizers to the water table . The δ15N volue is very similar to that of the soil organic nitrogen, for which δ15N volues are typically in the range +4‰- +8‰. Therefore, groundwater intrate result from the oxidation of part of the organic nirogen in the soil from crop plowing.
Some of the city supply well water samples δ15N values of +10‰ or less and overlap with the δ15N range of nitrater from the cultivation well water. The more negative δ15N values for groundwater intrate from city supply wells may indicater that cultivation nitrogen is the domi-nant source in these waters It's possible that regional groundwater flow transports soil nitrater from cultivated fields to the city supply wells.
The δ15N values for two samples from supply wells are +13.0‰ and +17.7‰. These are in the range of animal waste δ15N values (+10‰-+20‰). Therefore, groundwater from the two wells are contaminated with nitrate form animal wastes. |
| Jiao Pengcheng.1996.15N/14N Ratios of Ground Water Nitrate in Shijiazhuang City[J].Acta Geoscientica Sinica,17(z1):181-188. |
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