Investigation and Spatial Distribution on Nitrate Contamination in Water of Tianjin

The status of the nitrate contamination in water were investigated by sampling for 201 samples in Tianjin area.The results showed that there were significant differences on nitrate concentration in different types of water.Among them, the main reservoirs and rivers did not polluted by nitrate but there was a trend of nitrate contamination in little part of sewage drainage river and drainage ditch.The nitrate concentration in groundwater was higher with the average level 15.56 mg·L-1.With the groundwater depth increasing, there was an obvious decreasing trend of nitrate concentration in groundwater.The nitrate contamination was serious in the 0～100 m depth shallow groundwater.Especially there was very serious for nitrate contamination in the 0～50 m depth shallow groundwater but the nitrate pollution did not taken place in the groundwater under 100 m depth.However there was a high correlation between the extent of nitrate pollution of shallow groundwater and cropping types in agricultural area.In the most of vegetable planting areas, the nitrate pollution had been very serious in the shallow groundwater.The map of spatial distribution of nitrate concentration in groundwater was plotted by Kriging method.The results indicated that there were significant regional differences on nitrate contamination of groundwater in Tianjin area.The areas with higher nitrate concentration in groundwater were mainly distributed in vegetable fields for Wuqing, Xiqing, Jinghai and Baodi District etc., respectively.The levels of fertilizer application were investigated from the farmer questionnaire.It showed that there was a positive correlation between nitrate concentrate in groundwater and the level of nitrogen application in the vegetable field.The high level of nitrogen application was main route which resulted in nitrate pollution in groundwater in Tianjin vegetable area.