The Study On Transport Of Soil Nitrate Nitrogen And Numerical Simulation Of Groundwater Contamination In Plain Areas Of Hebei

Groundwater occupies an important position in the field of industry, agriculture andresidents living, the security problem in groundwater also directly affects the quality ofpeople’s life. In recent years, with the increase of pesticide and fertilizer usage,groundwater nitrate pollution caused by the fertilizer leaching is becoming more and moreserious. In order to research the non-point source pollution of groundwater caused byagricultural activities in Hebei plain, the leaching of nitrate nitrogen was studied in thismaster thesis. On the base of the measured data of hydrological, meteorological, fieldexperiment and groundwater quality in the Shijin irrigation area of Shijiazhuang, the modelthat was used to study the transporting of groundwater was established based on thenumerical simulation software of Visual MODFLOW. This article explored the migrationand transformation rule of the nitrate nitrogen in farmland soil profile by the fieldexperiment and used MODFLOW to simulate the nitrate nitrogen pollution of groundwater.The result can provide reference for guiding agricultural production and controllingagricultural non-point source pollution of groundwater.The study area which is named Shijin Irrigation District is one of the large-scaleirrigation area in Hebei Province and is located in the south-central district of Hebei Plain.It is a typical north China Plain irrigation area on the aspects of hydro-climatic, agriculturalplanting and management. Field experiment with numerical simulation software combinedin this paper. Field experiment mainly included the observation of soil nitrate nitrogencontent and soil moisture in different depth, as well as the regular observation ofgroundwater level and quality. In the numerical simulation, the article reasonably dividedthe whole district and correctly selected the hydrogeological parameters to establish ahydrological model with high reliability in the study area. Used the data of groundwaterlevel and nitrate leaching realizing as the input data of the model to simulate the water andnitrogen migration in the saturated soil zone. Run the model to forecast the level ofgroundwater nitrate nitrogen pollution under the different conditions of rainfall, irrigationand fertilization. The establishment of groundwater nitrate mig36,ration simulation model and the dynamic prediction of groundwater pollution in different hydrological years are thekeys to this thesis.The thesis’s simulation period was from November2011to October2012. Stressperiod was determined according to the date of the field experiment, with every three daysas a time step. The period from November19,2011to June2,2012was the recognitionstage in the simulation; the period from June3,2012to October5,2012was the validationphase. Based on soil properties and hydrogeological conditions of the study area, theaquifer was outlined as a layer in vertical direction. Due to the different irrigationconditions, the horizontal direction of the study area was divided into three districts,respectively well irrigation in northwest area, canal irrigation in southeast area and the wellcanal joint irrigation area in central. In order to analyze groundwater nitrate pollution underdifferent conditions of rainfall, irrigation, the paper separately selected rainfall series fromwet and dry years and set different irrigation and fertilization measures, using the verifiedmodel to study the long-term rule of groundwater nitrate leaching and accumulation in thestudy area. The results showed that the conventional experience fertilization volume hadcaused the nitrate pollution of shallow groundwater, canal irrigation area was more seriousand well irrigation area was lighter. Under general conditions, the nitrate migration rategradually slowed down with the increase of depth, so shallow groundwater quality was notsignificantly deteriorated in the short term. However, continuous pumping of groundwaterfor irrigation speeded up the vertical migration rate of nitrate, also posed a threat for thedeep groundwater environment. The result shows that rainfall is the most important factorof nitrate deep leaching, nitrate is also more sensitive to the amount of irrigation factorsthrough dynamic prediction. Therefore, in the actual agricultural production, the irrigationarea can control irrigation water to achieve the purpose of retarding the nitrate pollution ofgroundwater by the corresponding water-saving reform measures.