Risk Assessment On Non-point Nitrogen Pollution In Groundwater

With the development of agricultural modernization, the use of Nitrogen fertilizeris on the rise, but the nitrogen of crop uptake is a fixed value, so a large amount ofnitrogen will remain in the soil that increases the possibility of groundwatercontamination. China is seriously deficient in fresh water resources, in many placesthe water for production of industry and agriculture and for people’s life depends ongroundwater, thus groundwater protection is of great importance. It is necessary toevaluate the risks of groundwater nitrate pollution, according to the evaluation result,guide the suitable development and use of groundwater resources, in order to ensurethe sustainable development and utilization of groundwater resources.On the base of a large number of relevant papers and literature, this paperproposes three means that overlay and index methods, numerical mode means,analytical model means to evaluate the risks of groundwater nitrate pollution,according to the abundance of basic data in the researched region and differentmethods of risk index computing, and conducts three application studies of practicalcase in the middle of Jilin Province, main results for this study are as follows:(1) Overlay and index methods was established to evaluate the risks ofgroundwater nitrate pollution for area without abundant basic data, and risk index wascalculated by overlaying the product of weights times grades: selected11appraisaltargets and constructed an index system of overlay and index methods, on the basis ofdeeply analysis of natural factors and agricultural factors that influence the pollutionrisk of farmland groundwater, then made the scoring criteria and assigned the weightfor all indicators, and sat up the risk index evaluating model, finally translate theevaluation results into risk maps. The results of the application study of practical casein the middle of Jilin Province as follows: the risk of groundwater nitrate pollutionwas in imbalance with the characteristic that the east was higher than the west and thenorth was higher than the south; the region with higher risk appeared in Changchunand the highest located at the junction of Dehui and Yulin, as the region with thelowest risk appeared in Gongzhuling. (2) In view of transfer function, analytical model means was established toevaluate the risks of groundwater nitrate pollution for area without abundant basicdata, probability density function of solute travel time was used to describe thecharacteristics of nitrogen transport and transformation in soil, and risk index wasrefered to the amount of nitrogen leached into groundwater. The process of localagricultural production in typical black soil planting area was simulated withanalytical model means, the results show that the amount of nitrogen leached fromthe simulated soil was12kg N/hm2, the risk of groundwater nitrate pollution is at levelone.（3）With the software of hydrus, numerical mode means was established toevaluate the risks of groundwater nitrate pollution for area with abundant basic data,and risk index was divided by the amount of nitrogen leached into groundwater,which was calculated through the outputs of software. Five typical planting area wereselected in the middle of Jilin Province for evaluating groundwater pollution risk bythe numerical mode means, and local weather conditions, hydrological geologicalconditions, agricultural activity and crop growth was inputted into the software, theresearch result shows that: the largest number of ammonium nitrogen accumulated inthe Albic soil planting area, the least in the Alluvial soil planting area, as the largestand the least number of nitrate nitrogen accumulated in the Alluvial soil and Meadowsoil planting area; nitrate nitrogen transported more quickly than ammonium nitrogenand penetrated the entire soil layer in the third year in all planting area; the amount ofnitrogen leached from the simulated soil as follows:1.53、33.7、13.5、3.2和1.2kgN/hm2, that is, the risk of groundwater nitrate pollution is at level two for alluvial soilplanting areas, as other areas were at level one.