运用氮、氧双同位素技术研究永安江硝酸盐来源

Identification of Sources of Nitrate in the Yongan River With Isotopic Technology

以洱海人湖河流永安江为研究对象,利用硝酸盐δ15N 和δ180 双同位素技术对永安江水体的硝酸盐氮来源进行识别.在永安江沿程共布置9 个监测点,分析硝酸盐的污染特征,并利用离子交换树脂法对水样进行预处理后测试硝酸盐δ15N 和δ180 .结果表明,永安江硝酸盐氮源负荷占永安江总氮源污染的5 0 % 左右,各采样点p（硝酸盐）为0 . 07-5. 22 m g. L^-1,均值为1. 00-2. 39 mg · L^-1.经同位素测试,各采样点5 15N-N0 3-均值为6. 1 2 % c-13.88%C,5 180-N0 3-均值为8 .24%c- 1 1 . 7 2 % c;永安江河水中硝酸盐主要来自于流域内化学肥料、牲畜粪便、生活污水和土壤有机氮硝化;利用IsoSource混合模型对4 种形态的硝酸盐来源进行定量分析,发现化学肥料占37. 3 % ,牲畜粪便占34. 6 % ,村落污水占18. 2 % ,土壤有机氮占9. 9 % .利用IsoSource混合模型可为河流硝酸盐来源定量研究提供新的研究思路,硝酸盐贡献比例与河流流经村落位置及土地利用类型有关.

A case study of the Yongan River,a major inflow of the Erhai Lake,was conducted to identify sources of nitrate-N in the river water with the !15N-NO3-and !18O-NO3-double isotope technique. Along the river,9 monitoring sites were set up,responsible for characterizing nitrate pollution of the water,and measuring nitrate !15N-NO3-and !18O-NO3-in the water samples after treatment with ion exchange resin. Results show that the nitrate sources along the Yongan River are responsible for about 50% of the total nitrogen pollution load in the water. Nitrate concentration in the water samples at the monitoring sites varied in the range of 0. 07- 5. 22 mg·L-1,with mean being in the range of 1. 00-2. 39 mg·L-1.The isotope test reveals that the mean !15N-NO3-of the water samples at the monitoring sites ranged from 6. 12‰ to13. 88‰,and the mean !18O-NO3-did from 8. 24‰ to 11. 72‰. The findings demonstrate that the nitrate pollutant in the river comes mainly from chemical fertilization,livestock manure,domestic sewage,and nitrification of organic nitrogen in the soil in the valley. Quantification of contributions of the four sources with the Iso Source mixing model tells that 37. 3%was attributed to chemical fertilization,34. 6% to disposal of livestock manure,18.2% to discharge of rural domestic sewage and 9. 9% to nitrification of organic nitrogen in the soil. The experiment shows that the use of the Iso Source mixed model to quantify sources of nitrate pollutant in the river may provide future studies with a new train of thought and that ratio of the contributions of the sources to the total nitrate pollutant in the river is related to location of the villages the river runs through and type of land use therein.