Characteristics And Trends Of Nitrates In Shallow Groundwater In The Middle Of The Hutuo River Alluvial Fan,Shijiazhuang

The study area is located in the Hutuo River alluvial fan in Shijiazhuang.The results of previous studies on nitrate in the area showed that the concentration of nitrate in the groundwater had been continuously increasing,and the water quality had been continuously deteriorating.Combined with the meteorological,hydrological,geological,hydrogeological and multi-year monitoring data of groundwater level and water quality in the area,the methods of the geological statistics and numerical simulation were used to analyze the characteristics of nitrate in the groundwater of this area.The trends of nitrate concentration in the groundwater were predicted under the influence of convection,dispersion and three different intensities of human activities,so as to provide scientific basis for groundwater protection in the area.The main conclusions are as follows:（1）The main cation in the groundwater in the study area is Ca²⁺,the main anion is HCO₃^-.The total dissolved solids（TDS）of the groundwater is relatively high,and the average value is 622.08 mg/L.The correlation coefficient between NO₃^-and TDS is 0.924,showing a significant positive correlation.The distribution of nitrate ions in the groundwater is uneven,and the concentration near the agricultural and forestry farms in the cadre school reaches 145.64 mg/L.The area with the nitrate ion concentration greater than 88.6 mg/L（Class III,GB/T 14848-2017）is 34.76km²,and its shape is oval.（2）By establishing the nitrate transport model in the groundwater of the study area,human activity intensity was defined as three different types:maintained,weakened,and enhanced.The variation trends of nitrate ions in groundwater in the area under different human activity intensity were calculated separately.The following conclusions were summarized.The maximum concentration of nitrate ion in the groundwater would increase from 145.64 mg/L to 162.12mg/L,and the area with the nitrate ion concentration greater than 88.6 mg/L would increase from34.76km² to 38.32km² between 2018 and 2028 if the intensity of human activity was maintained.The maximum concentration of nitrate ion would reduce to 117.72mg/L,and the area with the nitrate ion concentration greater than 88.6 mg/L would reduce to 18.06km² by 2028 if the intensity of human activity was weakened.The maximum concentration of nitrate ion would increase to 190.86mg/L,and the area with the nitrate ion concentration greater than 88.6 mg/L would increase to 61.58km² by 2028if the intensity of human activity was enhanced.（3）The dispersion scale effect of the solute transport model was analyzed.The maximum value of nitrate in the contaminated plume would decrease with the increase of the dispersion value,but the morphology of the contaminated plume would remain unchanged.（4）The influence degree of reduce exploitation and the Hutuo River recharge project was simulated in the groundwater flow numerical model.The results showed that the maximum value of groundwater level in the study area would increase 1⁴m between 2017 and 2028.