基于水化学及氮氧同位素技术的硝酸盐来源解析——以鄱阳湖湿地为例

为了识别鄱阳湖湿地水体中硝酸盐污染的来源,转化特征和各污染来源的贡献比例,选取枯水期这一典型时期,于2019年1月份对鄱阳湖中的蚌湖湿地,沙湖山湿地和庐山湿地的地表水进行取样,并测定了水样中的离子组成和硝酸盐氮氧同位素值.研究结果显示, NO3-/Cl-物质的量浓度比值与Cl-浓度的关系表明3处湿地中硝酸盐来源可能受到农业活动和降雨的影响.蚌湖,沙湖山和庐山湿地水体中δ15N-NO3-和δ18O-NO3-值的范围分别为-6.19‰～4.67‰和3.41‰～39.95‰,-4.14‰～1.45‰和31.54‰～68.30‰,-6.98‰～3.83‰和2.80‰～30.43‰,硝酸盐氮氧同位素值表明3处湿地硝酸盐来源可能受到降水NO3-,硝酸盐氮肥,氨态氮肥和土壤有机氮的影响.利用硝酸盐氮氧同位素之间的关系,并结合NO3-与Cl-比值关系判断湿地中无明显反硝化作用的发生.SIAR模型结果显示:蚌湖湿地,沙湖山湿地,庐山湿地硝酸盐来源中降水NO3-贡献占比最大,其次是化肥,土壤有机氮,粪便和生活污水贡献占比最小.

Hydrochemistry,nitrogen and oxygen isotope composition of nitrate to trace its source in Poyang Lake wetland

In order to identify the sources, transformation and source apportionment of nitrate in Poyang lake wetland, surface water samples were collected in Poyang lake wetland, including Bang lake wetland, Shahushan wetland and Lushan wetland, in January 2019, a typical dry season. The ion composition, and nitrogen and oxygen isotope values of nitrate in the water samples were determined. Results showed that the relationship between the molar ratio of NO₃^- to Cl^- and Cl^- concentration indicated the source of nitrate mainly from agricultural activities and rainfall in the three wetlands. The range of δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^- values in the three wetlands were -6.19‰~4.67‰ and 3.41‰~39.95‰, -4.14‰~1.45‰ and 31.54‰~68.30‰, -6.98‰~3.83‰ and 2.80‰~ 30.43‰, respectively. Nitrogen and oxygen isotope values of nitrate showed that the nitrate sources may be influenced by precipitation NO₃^-, nitrate nitrogen fertilizer, ammonia nitrogen fertilizer and soil organic nitrogen in the three wetlands. The relationship between nitrogen and oxygen isotopes of nitrate and the ratio relationship between NO₃^- and Cl^- suggested that there was no obvious denitrification in these wetlands. The results of SIAR model showed that the contribution of precipitation NO₃^- to nitrate sources was the largest, then followed by fertilizer and soil organic nitrogen, feces and domestic sewage was the least in three wetlands.