九龙江流域地表水中硝酸盐来源辨析

从九龙江流域遴选出2个典型小流域--仙都和五川小流域作为研究区,于2005年春季运用15N同位素示踪法对其地表水中硝酸盐来源进行研究.结果表明,仙都小流域地表水中溶解态总氮、硝氮和氨氮的浓度范围(以N计,下同)分别为1.47～5.31 mg/L、0.83～4.05mg/L和0.21～0.36mg/L,硝酸盐的δ15N值(以样品相对于标准大气N2的15N和14N比值的千分偏差表示)范围在2.5460-7.92%之间;五川小流域地表水中溶解态总氮、硝氮和氨氮的浓度范围分别为1.14～5.56mg/L、0.96～1.46mg/L和0.12～1.28mg/L,硝酸盐的δ15N值范围在-0.19‰～5.89‰之间.对照不同来源的硝酸盐δ15N特征值,结合研究区的农作物种植和施肥状况,得出如下结论:仙都小流域地表水中硝酸盐主要来自无机化肥与土壤有机氮,有机肥有一定的贡献;五川小流域地表水中硝酸盐的来源以无机化肥与土壤有机氮为主,有机肥的贡献很小;2个小流域地表水中硝酸盐的来源随时空变化而有差异,与当地农作物种类及农田时令密切相关.

Identifying Sources of Nitrate in Surface Water of Jiulong River Watershed

Two representative catchments, Wuchuang catchment and Xiandu catchment, were selected from Jiulong River Watershed as study areas to trace sources of nitrate in surface water by using 15N isotope technique. In the spring of 2005, the surface water samples were twice collected from the catchments and determined for dissolved total nitrogen (DTN), nitrate nitrogen (NO3(-)-N), ammonia nitrogen (NH4+-N) and delta 15N value of nitrate. The results showed that in the samples from Xiandu catchment, the concentration ranges of DTN, NO3(-)-N and NH4+-N were 1.47-5.31 mg/L, 0.83-4.05 mg/L and 0.21-0.36 mg/L respectively, and the delta 15N values of nitrate ranged from 2.54 per thousand to 7.92 per thousand; in the samples from Wuchuang catchment, the concentration ranges of DTN, NO3(-)-N and NH4+-N were 1.14-5.56 mg/L, 0.96-1.46 mg/L and 0.12-1.28 mg/L respectively, and the delta 15N values of nitrate were between -0.19 per thousand and 5.89 per thousand. In contrast with the typical ranges of delta 15N isotopic signature of nitrate from different sources and in consideration of the information of local crop planting circumstances and application of fertilizers, the data indicated that the first, the nitrate in the surface water of Xindu catchment mainly came from inorganic fertilizers and soil organic nitrogen, and some originated from organic fertilizers; the second, the nitrate in the surface water of Wuchuang catchment mostly flowed from inorganic fertilizers and soil organic nitrogen, and few derived from organic fertilizers; the third, the sources of nitrate varied with the sampling location and time and were dependent on the kinds of local crops and their planting seasons.