| In this paper, Shicao town was selected as the study area for the high incidence of cancer of residents in Shenqiu County, Henan province, with the control area being selected in village Xinghuaying, Kaifeng city. Lots of water samples were collected in surface water and groundwater during dry season and wet season in both rural areas. Nitrate and nitrite nitrogen content of samples were determined by Auto-Analyzer (AA3) in laboratory. Then the distribution of nitrate and nitrite nitrogen contents were displayed with the aid of Matlab software, and the variation of nitrate and nitrite nitrogen contents were analyzed in the different seasons in a year. Comparing to national water standard, the assessment of the groundwater about the nitrogen pollution had been done. The sources of pollutants were discussed for water protection. The main conclusions of this study can be summed up as follows:(1)There was no significant difference between the wet seasons and dry seasons about the contents of nitrate and nitrite in surface water. However, there was significant difference between the two seasons about nitrate nitrogen in groundwater, but no difference about nitrite nitrogen. The average of surface water in rainy and drought season about nitrate nitrogen concentration (1.39 mg·L-1 and 1.24 mg·L-1, respectively) and the average concentration of nitrite nitrogen in two seasons (0.08 mg·L-1 and 0.07 mg·L-1, respectively) were very close, while the average nitrate nitrogen of groundwater in rainy season (7.87 mg·L-1) was higher than that in dry season (1.90 mg·L-1), with the same mean of nitrite nitrogen was 0.03 mg·L-1 in two seasons.(2)There were clear regional differences with spatial distribution about nitrate and nitrite nitrogen of water in Shicao town. The spatial distribution of nitrate was very similar to the distribution of nitrite nitrogen in surface water in rainy season. The samples with higher content were distributed in the township of the government of shicao and the north of the region, where vegetables were planted as an important growing area. The spatial variation of nitrate nitrogen of groundwater was higher than that of nitrite in rainy season. The samples with higher value of nitrate nitrogen contents in groundwater were located in Zhangying village and 7 villages nearby than the other place. Nitrite nitrogen content in shicao Township government, Beihu village and shaozhuang village were higher than the other villages. The nitrate and nitrite nitrogen of contents surface water were uniform in the spatial distribution in dry season. Spatial variation of nitrate nitrogen in groundwater during the dry season was lower than that of nitrite nitrogen.(3)The excessive use of fertilizer in agriculture was the main reason for nitrate pollution of groundwater. The sampling sites with higher nitrate and nitrite nitrogen content of groundwater than national standard located in vegetable land and cropland mostly, with the highest value of nitrate content of groundwater locating in vegetable land. 7 water samples, of which the nitrate content were more than 30 mg·L-1, was including 3 samples collected from vegetable land. While the other samples with higher nitrate nitrogen content were not only from the places where no vegetable had been planted. It showed that the sewage of residential areas and animal manure should be the main source of nitrate nitrogen to groundwater in these places.(4)In the study area, the pollution of nitrate and nitrite nitrogen was serious, while part of the shallow groundwater was not suitable for drinking. The nitrate nitrogen content of some groundwater samples got from the township government of shicao and the southern villages, including Yangying, Chenzhuang and Wanghu Village, were higher than the threshold values in gradeⅤof national groundwater quality standards. Residential groundwater nitrite nitrogen partially exceeded the threshold of the standard. It showed that serious contamination had happened. The average content of groundwater about nitrite nitrogen was 0.01 mg·L-1in rainy season, the average of nitrite nitrogen content about groundwater during dry season was 0.04 mg·L-1. For the all, there were 13.1% and 13.3% of the wells, in which nitrite nitrogen were higher than the value of GradeⅢin National Groundwater Quality (GB/T14848-93) in the town in rainy and dry season, respectively.Overall, the local groundwater pollution was deteriorating. Great risks to the health of local residents when they were drinking the water without any treatment would be paid more attention in future.
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