贵阳地区夏季雨水硫和氮同位素地球化学特征

Geochemical characteristics of sulfur and nitrogen isotopic compositions in rains of Guiyang in summer

对贵阳地区小雨和暴雨硫和氮同位素组成特征进行了研究。小雨中硫酸盐δ34S值和硝酸盐δ15N值分别为-7.96‰～+0.73‰(平均-4.90‰)和-3.77‰～+8.49‰(平均+2.00‰),暴雨中则分别为-2.07‰～+18.32‰(平均+4.59‰)和-2.91‰～+10.10‰(平均+4.10‰),表明两种类型雨水中硫酸盐和硝酸盐来源不同。小雨硫酸盐的负δ34S值与当地硫来源(煤炭燃烧和生物成因硫)有关,而暴雨硫酸盐的正δ34S值则为海源(太平洋)结果。小雨硝酸盐的δ15N值范围较宽(-3.77‰～+8.49‰),其来源不清,但该范围内较高δ15N值的样品(>+6.0‰)可能与干沉降和火力发电厂废气有关。暴雨硝酸盐的δ15N值仍然反映海源(太平洋)。小雨铵盐的δ15N值与铵盐含量有较好的相关关系(R2=0.92)。小雨铵盐中低δ15N值的样品(-1.73‰～-22.01‰)与云水(-28.6‰)对15N较少的吸收有关。贵阳地区较高的铵盐含量(平均1.25mg/L)和较低的δ15N值(平均-12.18‰±6.68‰)表明,铵盐来源于农业肥料的大范围施用和土壤NH3的挥发。

A significant difference in mean sul fur and nitrogen isotopic composition is seen between samples collected from flurries(-4.90‰for sulfate and +2.00‰for nitrate)and storms (+4.59‰for sulfate and+4.10‰for nitrate),showing that sulfur and nitrogen in the two types of rains are of differen ce sources.For sulfate,the negativeδ 34 S values in flurries are associated with local sources(coal combustion and biogenic sulfur );while sulfur in storms,caused by typ hoon from the Pacific,with positiveδ 34 S values are of maritime origin.For nitrate,the sources in flurries are not much clear because of a wide range ofδ 15 N values(-3.77‰～+8.49‰),but the higherδ 15 N values(>+6.0‰)in the range are probably related to d ry deposition or thermoelectric pow er stations;the meanδ 15 N value of +4.1‰in storms may also be a reflection of maritime origin.Measurements ofδ 15 N values for ammonium in flurries show thatδ 15 N values are well related with ammoni um concentrations(R 2 =0.92).The lower values in the range ofδ 15 N values(-1.73‰～-22.01‰)for ammonium are due to the less incorporation of 15 N by cloud water,which probably has a δ 15 N value of about -28.6‰.But the higher concentrations and the lowerδ 15 N values(averaged -12.18‰±6.68‰)indicate that sources of ammonium are widespread agricultural use of excretory wastes and the release of NH 3 from soils.