太湖西苕溪流域地表水、地下水硝酸盐污染特征及来源

Characteristics and Potential Sources of Nitrate Pollution in Surface and Ground Water in Xitiaoxi River,Taihu Lake Basin

为探寻西苕溪流域地下水中NO3--N的污染来源,对西苕溪流域地表水、地下水体的NO3--N污染状况进行了调查,并结合水化学与NO3--N同位素对其来源进行解析.结果显示,西苕溪流域地表水的ρ(NO3--N)为1.07～3.45 mg/L,ρ(NO2--N)为0.15～0.35 mg/L;地下水中ρ(NO3--N)为3.24～15.31 mg/L,平均值达9.26 mgL.下游地区地下水的ρ(NO2--N)较高(0.26～4.25 mg/L),平均值达3.00 mg/L.ρ(NO3-)与ρ(Cl-)的关系显示,西苕溪地表水、地下水存在比较稳定的NO3--N输入来源.NO3--N同位素分析结果显示,地表水的δ15N为7.0‰～16.7‰,说明上游NO3--N主要来源于土壤有机氮的矿化,中下游则主要受到农业施用化肥与人类生活污水二者的共同影响;地下水的δ15N为14.3‰～27.1‰,说明调查区域内的地下水受人畜粪便和生活污水的影响可能更为强烈,另外,地下水中存在的反硝化作用也是造成地下水δ15N增高的原因.

To assess nitrate pollution and identify its potential sources, surface and ground water samples in Xitiaoxi River of the Taihu basin, China, were collected for analysis of the hydrochemistry and environmental isotope characteristics. The results show that the concentrations of NO3 - -N and NO2 - -N in the surface water were in the ranges of 1.07-3.45 and 0. 15-0.35 mg/L, respectively. However, the concentration of NO3 - -N in the ground water was in the range of 3.24-15.31 mg/L, with an average of 9. 26 mg/L. The concentration of NO= - -N in the downstream part of the river was 0.26-4.25 mg/L, with a mean of 3.00 mg/L. The relationship between concentrations of NO3 - and C1- in both surface and ground water were significant, and suggested that they may be from a common source. Analysis of the environmental isotopes showed that the δ15 N values in the surface water ranged from 7.0‰ to 16.7%. The lower 815 N values occurring in the upstream part indicated a major source of mineralization of the soil organic nitrogen, and chemical fertilizer and sewage may be two potential sources of nitrate in the middle and lower reaches. However, the ground water in the river basin may be mainly influenced by sewage, with higher δ15N values from 14. 3‰ to 27.1‰. In addition, the results also indicated that denitrifieation in the ground water may also play an important role in the increase of the δ15N values.