利用氮同位素技术探讨天津地表水氮污染

Nitrogen pollution of surface water in Tianjin based on nitrogen isotope approach

地表水的氮污染状况与水质、区域景观等密切相连。本文分析了天津地表水的三氮(NO3-N、NH4+-N、NO2-N)组成,以及部分水样NO3-N和NH4+-N的N同位素组成。结果显示:NO3-N的含量为0.01～16.51mg.L-1,均值为2.25mg.L-1,部分样品NO3-的含量超过50mg.L-1(以NO3-N计为11.29mg.L-1);NH4+-N的含量为0～10.60mg.L-1,均值为1.15mg.L-1,有1/4水样超过1.5mg.L-1;另外,在所有样品中有1/12水样有较高的NO2-N。NO3-N为大部分水样无机氮的主要形态,污水等部分水样以NH4+-N为主要形态。NO3-N同位素值的变化范围为-5.5‰～+28.6‰,均值为+9.0‰(n=49),中值为+8.5‰;NH4+-N同位素值的变化范围为-8.8‰～+34.3‰,均值+11.6‰(n=11),中值为+13.6‰。水化学和同位素结果分析表明,该区地表水的氮主要来源为生活污水,而且氮形态转化受硝化作用、挥发作用以及可能的反硝化作用影响明显。

In order to understand the situation of surface water nitrogen pollution in Tianjin,this paper analyzed the nitrogen （nitrate,ammonium,and nitrite） concentrations in the river,reservoir,salt water,and sewage,and the isotopic composition of nitrate-and ammonium nitrogen in most water samples.The NO-3-N concentration in the waters ranged from 0.01 mg·L-1 to 16.51 mg·L-1,with a mean value of 2.25 mg·L-1.Some waters had the NO-3 concentration 50 mg·L-1 （11.29 mg·L-1 of NO-3-N）,showing their high nitrate pollution.The NH＋4-N concentration in the waters was from 0 to 10.60 mg·L-1,with a mean value of 1.15 mg·L-1.One fourth of the waters had the NH＋4-N concentration 1.5 mg·L-1.About 1/12 of the waters had higher NO-2-N.In most water samples,nitrate was the dominant species of inorganic nitrogen.Ammonium was the main nitrogen species in some waters,especially in sewage.The δ15NO-3-N value ranged from-5.5‰ to ＋28.6‰ （n=49,mean ＋9.0‰,median ＋8.5‰）,and the δ15NH＋4-N value ranged from-8.8‰ to ＋34.3‰ （n=11,mean ＋11.6‰,median ＋13.6‰）.All the results suggested that domestic sewage was the main source of surface water nitrogen pollution in Tianjin,and the nitrogen isotopic composition was obviously affected by nitrification,ammonia volatilization,and denitrification.