Nitrogen Source And Transformation In Groundwater And Fluvo-aquic Soil Of Hebei Plain

Groundwater was one of the main source of human drinking water,but its pollution was increasingly serious.Among them,nitrogen pollution of groundwater always was one environmental problem which caused worldwide concern of people.Nitrogen entered into the groundwater through the vadose zone mainly,then cause the pollution of groundwater.Thus,it was very important to study on the sources and transformation of nitrogen.This paper was aimed at shallow groundwater and vadose zone of fluvo-aquic soil in Hebei Plain as object of study.According to the current pollution situation of shallow groundwater,identified the sources of nitrogen using the nitrogen and oxygen isotope technical.At the same time,through the soil columns leaching experiment elucidated the mechanisms of transformation and simulated it which using software of Hydrus-1D.Thus it will provide some suggestions for pollution control of groundwater.The following were main results:In Hebei plain,the average concentration of NO₃^--N in the Central plain was 4.44 mg×L-1,it's the smallest in the three sub-plains;the average concentration of NO₃^--N in the Eastern Coastal plain was 31.52 mg×L-1,it's the biggest one which the pollution was the most seriously in Hebei Pain.And in the year of 2009²014,the average concentration of NO₃^--N was 18.72 mg×L-1,it exceeded 0.872 times by the American Drinking Water Standard.The result of isotope showed that the NO₃^--N come from septic waste in the Eastern Coastal plain and the Central plain,and in the Piedmont plain,apart from septic wastes,the NO₃^--N also come from fertilizers.Selecting fluvo-aquic soil as research subjects in the soil columns leaching experiment,the average concentration of nitrate was 1.68 mg·L-1,ammonia nitrogen was 13.56 mg·L-1,nitrite was 0.23 mg·L-1 in the Piedmont plain;the average concentration of nitrate was 1.08 mg·L-1,ammonia nitrogen was 13.95 mg·L-1 and nitrite was 0.11 mg·L-1 in the Central plain.In the Piedmont plain,the concentration of NO₃^--N was increased in the period of 96¹92 h,and was decomposed with oxygen consumed eventually,The maximum concentration of ammonia nitrogen was appeared in the lowest layer;the nitrite concentration decreased drastically in the initial stage,then rised.In the Central plain,NO₃^--N accumulated in the surface of soil;The concentration of ammonia nitrogen reached the maximum concentration in 480 h;nitrite concentration accumulated more in the depths of 20 cm.Using Hydrus-1D software to simulate and predicte the soil moisture transfer and solute transport model in the fluvo-aquic soil,the nitrate maximum absolute error was 0.033,the ammonia nitrogen maximum absolute error was 1.076,the experimental and simulated values were similar.Therefore,Hydrus-1D software is good for simulation and prediction of the nitrate and ammonia nitrogen in fluvo-aquic soil.