| Groundwater mineral nitrogen pollution is a widespread water environment problem at home and abroad,and Guanzhong Basin was one of the earliest researchers to pay attention to groundwater mineral nitrogen pollution.As the main source of living for people in the area,the safety of groundwater quality is of great significance to human health.In this dissertation,the groundwater mineral nitrogen(ammonia nitrogen,nitrate nitrogen and nitrite nitrogen)in the Guanzhong Basin was sampled and monitored by the grid method to understand the characteristics of groundwater mineral nitrogen pollution in the area and the characteristics of spatial and temporal changes.The main sources of mineral nitrogen pollution in groundwater were analyzed.Obtain the following research results:1.The contents of ammonia nitrogen,nitrate nitrogen,and nitrite nitrogen in groundwater in the Guanzhong Basin were 0~1.48 mg/L(mean 0.06 mg/L),0~27.86 mg/L(mean 4.86 mg/L),and 0~ 1.86 mg/L(mean value: 0.05 mg/L),and the percentage of three kinds of mineral nitrogen exceeded(GB/T14848-2017 groundwater quality standards in China)was 0.47%,2.35%,and 0.47%,respectively.Nitrate nitrogen is the most serious pollution of the three kinds of mineral nitrogen,but the content of mineral nitrogen and the rate of exceeding the standard are lower than most other areas of China.2.The nitrate content of groundwater in the south part of the Guanzhong basin is slightly higher than that in the north,and the content of ammonia nitrogen and nitrite nitrogen in the northern part is slightly higher than that in the south.Exceeding areas are mainly distributed in areas such as Baoji-Mei County,Wugong-Xingping,Fuping-Pucheng and Linyi.The order of ammonia nitrogen pollution in the four districts of Guanzhong Basin is Weinan> Xianyang> Xi’an> Baoji.The order of nitrate pollution is Baoji> Xianyang> Xi’an> Weinan,and the order of nitrite nitrogen is Weinan> Xianyang> Baoji> Xi’an.There is a negative correlation between groundwater mineral nitrogen pollution and groundwater depth in Guanzhong Basin.3.Mineral nitrogen in groundwater during the flood season in the Guanzhong Basin is lower than the dry season.For more than 30 years,the nitrate pollution in the groundwater of the Guanzhong Basin has increased first and then decreased.From 1980 s to 2000 s,the nitrate content of groundwater increased from 8.8 mg/L to 19.45 mg/L,but by 2017,the nitrate The content was reduced to 4.86 mg/L.Therefore,the nitrate pollution of groundwater in Guanzhong Basin has been well controlled.4.Sampling surveys have revealed the phenomenon of nitrate nitrogen leaching in the farmland of the Guanzhong Basin.Especially in orchards with high fertilization rates,nitrate nitrogen can be soaked in deep soil layers up to 3 m.However,it is considered that fertilization is not groundwater nitrate in Guanzhong Basin.The main source of nitrogen.The trend of nitrate nitrogen in groundwater over the past 30 years in the Guanzhong Basin was inconsistent with the amount of fertilizer applied to the farmland,but it was consistent with the variation of nitrogen concentration in the surface water(including the Yellow River,the Wei River,and its tributaries)that flowed through the area.In addition,there is a very significant positive correlation between the nitrate content in groundwater and chloride ion content.This shows that the domestic sewage and industrial wastewater discharge is the main source of nitrate in groundwater in the Guanzhong Basin.At present,the improvement of the groundwater quality in this area has a direct relationship with the local government’s strong control measures for surface environmental quality. |
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