青岛市农区地下水硝态氮污染来源解析

Identifying the Sources of Groudwater NO-Nin Agricultural Region of Qingdao

为了提高作物产量,肥料大量投入在农业种植区日益普遍,导致了农区地下水硝态氮(NO^(-)_(3)-N)污染.农业面源污染是地下水硝态氮污染的主要原因.为了保障饮用水安全,明确农区硝态氮污染的来源是十分必要的.本研究分别于2009年和2019年在青岛农区随机选取35个采样点,借助反距离加权法(IDW)对硝态氮含量进行空间分布分析,通过测定氮、氧同位素进行溯源,运用SIAR模型量化污染源的贡献率.结果表明,青岛市地下水硝态氮含量(平均值)由2009年的38.49 mg·L^(-1)降低为2019年的22.37 mg·L^(-1),但仍高于世界卫生组织(WHO)规定的饮用水中硝态氮的最大允许含量.2009年和2019年硝态氮含量都呈现由南向北逐渐增加的趋势,南部污染轻,北部污染重.δ^(15)N-NO^(-)_(3)和δ^(18)O-NO^(-)_(3)的交叉图显示青岛市地下水硝态氮主要来源是化肥、土壤氮、粪肥和污水.水同位素表明降水是青岛市地下水的主要来源.贝叶斯混合模型(SIAR模型)表明污染源贡献率为:粪肥和污水(47.42%)>土壤氮(27.80%)>化肥(14.35%)>大气氮沉降(10.43%).从2009~2019年青岛市地下水质量得到了改善,但硝态氮污染状况仍不容忽视,应根据硝态氮污染来源,有针对性地防治以确保农区饮用水安全和农业的可持续发展.

To increase crops yields,applying large amounts of fertilizers has become increasingly common in agricultural regions,resulting in NO^(-)_(3)-N groundwater pollution.Agricultural non-point pollution is the main source of groundwater NO^(-)_(3)-N pollution.To ensure drinking water safety and quality,it is crucial to clarify the sources of NO^(-)_(3)-N pollution in agricultural regions.In this study,35sampling sites were randomly selected in the Qingdao agricultural area in 2009 and 2019.The spatial distribution of NO^(-)_(3)-Nconcentration was analyzed by the inverse distance weighting method (IDW).The nitrogen and oxygen isotopes were used as a tool to trace sources of NO^(-)_(3)-N and the SIAR model was used to quantify contribution proportion of pollution sources.The results showed that the concentration of NO^(-)_(3)-N (average) in groundwater in Qingdao has been reduced from 38.49 mg·L^(-1)in 2009 to 22.37 mg·L^(-1)in2019,but it is still higher than the maximum allowable concentration of NO^(-)_(3)-N in drinking water set by the World Health Organization(WHO).The NO^(-)_(3)-N concentration gradually increased from south to north both in 2009 and 2019.The cross diagram ofδ^(15)N-NO-3andδ^(18)O-NO-3show that the main sources of NO^(-)_(3)-N in groundwater in Qingdao are chemical fertilizers,soil nitrogen,and manure and sewage.Water isotopes indicate that precipitation was the main source of groundwater in Qingdao.The SIAR model results indicated that the contribution of each source ranked as follows:manure and sewage (47.42%)>soil nitrogen (27.80%)>chemical fertilizer(14.32%)>atmospheric nitrogen depositions (10.43%).From 2009 to 2019,the quality of groundwater in Qingdao has been improved,but NO^(-)_(3)-N pollution still cannot be ignored.According to the results,prevention and control should be made to ensure the safety of drinking water and the sustainable development of agriculture.