太湖流域长兴县浅层地下水氮污染特征及影响因素研究

摘要

Nitrogen pollution in the shallow groundwater in Changxing county of the Taihu basin was investigated.A total of 43 groundwater samples were collected and their ammonia,nitrate and nitrite concentrations were analyzed.The results show that 13.95％,16.27％,and 16.27％ of ammonia,nitrate and nitrite concentrations exceeded the standard.Nitrate pollution is serious in the agricultural areas near Jiapu,Xiaopu,Hongqiao and Hongxingqiao towns among which the Hongxingqiao town is the most serious with the maximum value of nitrate of 22 mg/L.A geostatistic method was used to quantify the spatial variation and correlation of the ammonia,nitrate and nitrite concentrations based on 43 groundwater samples.The result show that the spatial pattern of the nitrate-and nitrite-nitrogen concentration data can be described with a spherical model while that of the ammonia concentrations with a Gaussian model.The correlation distances of the ammonia-nitrogen,nitrate-nitrogen,nitrite-nitrogen concentrations were 9.98,1.51 and 3.82km,respectively.The results also show that nitrate-nitrogen concentrations in groundwater in this region were positively correlated to the rate of fertilizer application.The average of the groundwater nitrate-nitrogen concentrations is 6.7 mg/L in the areas where the annual fertilizer application was 300 kg/hm2 (N) and 2.2 mg/L in the area where the annual fertilizer application was 100 kg/hm2 (N) ; Groundwater nitrate-nitrogen concentrations were related to the depth to the water table:the shallower the water table,the higher the nitrate-nitrogen concentrations.Groundwater nitrate-nitrogen concentrations were also positively correlated to population density when the land use types are similar.%对太湖流域长兴县浅层地下水的氮污染进行了系统的调查与研究,共取地下水样43个并测定了其三氮含量.结果表明氨氮、硝酸盐和亚硝酸盐的超标率分别为13.95％、16.27％和16.27％.三氮污染最严重的地区主要为农业活动集中区,即夹浦镇、小浦镇、洪桥镇和虹星桥镇等,其中虹星桥镇硝酸盐污染最为严重,高达22mg/L.采用地质统计学方法对太湖流域长兴县43个浅层地下水样“三氮”含量进行了区域空间变异分析,结果表明长兴县地下水NO3-N和NO2-N浓度变异函数满足球状模型,而NH3-N浓度变异函数为高斯模型,硝酸盐氮、亚硝酸盐氮和氨氮浓度的空间自相关距离分别为9.98、1.51和3.82kmn.对硝酸盐污染因素进行了分析,结果表明:硝酸盐浓度与氮肥使用量呈明显正相关关系,年平均施肥量(以N计)为300kg/ha地区平均硝酸盐氮浓度达6.7mg/L,年平均施肥量(以N计)为100kg/ha地区平均硝酸盐氮浓度为2.2mg/L;地下水硝酸盐与地下水位埋深有直接关系,埋深较浅(1～3m)地区的硝酸盐浓度较高;当土地利用类型相同时,硝酸盐氮浓度与人口密度具有线性正相关关系.