| Non-point source pollution of agricultural is becoming the main source of water pollution, while nitrate nitrogen contamination has become a worldwide issue of common concern, and it is recognized as the most widespread groundwater pollutant. Yanqi Basin is located in the north of Bayinguoleng Mongolia Autonomous Prefecture of Xinjiang province, the plain area is the typical oasis in arid area. In recent years, the amount of nitrogen fertilizer application has been increasing continually in the intensive planting area of oasis, and the utilization rate is generally low, considering the wastewater emissions and so on, the nitrate nitrogen concentration of regional water have a trend of increasing in different degrees. Given this, combined with the collected relevant data including soil?nitrogen fertilizer amount?precipitation and so on, based on the field investigation and monitoring?indoor laboratory analysis, the paper summarized the nitrate nitrogen concentration of water of Yanqi Basin, combined GIS and geostatistics method to do quantitative analysis of the temporal and spatial distribution?evolutionary characteristics and trends of nitrate nitrogen of groundwate in the oasis area, the specific research conclusions are as follows:(1) The overall level of nitrate nitrogen concentration in water is at a low level in Yanqi Basin, and the nitrate nitrogen concentration has different distribution between different regions?the change of buried depth and different land use patterns and so on, because of the different influence of human factors. Comparing with the river, the differences between farmland irrigation and drainage canal section of water are more obvious, is significantly influenced by regional area, the difference of nitrate nitrogen concentration is more obvious between diffenent river section and different positions of Bosten lake. The average value of nitrate nitrogen concentration in groundwater is 2.38mg·L-1, which belongs to the ? class of groundwater quality in classification criteria. The distribution frequency of nitrate nitrogen concentration of different types of groundwater in oasis area shows that the nitrate nitrogen concentration in groundwater and its variation coefficient is negatively correlated with buried depth. The populous areas?nitrogen fertilizer biomass input?soil texture and lithological conditions are the factors of higher nitrate nitrogen concentration, parts of the region, especially shallow groundwater have higher nitrate nitrogen concentration, affected by human activity is very obvious and needs to be protected.(2) The nitrate nitrogen concentration of groundwater is accord with lognormal distribution, the Ordinary Kriging interpolation prediction conclusion shows that nitrate nitrogen concentration of phreastic water overall assumes circular gradient distribution, and is axisymmetric with Kaidu River, non directional effect, the higher nitrate nitrogen concentration region focus on peripheral of Hejing and Heshuo county and the both sides area of first canal of liberation irrigation, and was scattered distrabution. The large area of farmland irrigation confined goundwater quality is ? class, drinking tap water is I class. The spatial interpolation results of nitrate nitrogen concentration in different types of groundwater shows different distribution characteristics, the spatial distribution pattern of nitrate nitrogen concentration in groundwater further indicates that the distribution in oasis area has obvious regional difference.The overall distribution characteristics of confined water shows that the higher nitrate nitrogen concentration area is lies in the drainage area of farmland.(3) The applicability analysis of the ArcGIS Ordinary Kriging interpolation shows that the sample quantities is positively related with the determination coefficient, to separate diffenent water type has obvious effect on determination coefficient, reasonable arrangement of sampling position?quantity?distribution range?intensive and density have significant effect on the interpolation precision, the spatial interpolation analysis precision is more higher with separate different groundwater type and region. The nitrate nitrogen concentration spatial correlation distance of phreatic water, irrigation confined water, drinking tap water, oasis confined water and the total groundwater are 22m?198m?1579m?138m?17m respectively.(4) The space movement of nitrogen is including diffenent types of transformation after being into the soil, with the form of nitrate nitrogen into groundwater eventually, the amount of ammonium nitrogen concentration in soil is significantly more higher than that of nitrate nitrogen, the water of vadose zone is on the contrary, the analysis of soil profile distribution characteristics and accumulation coefficient for field nitrogen in different regional shows that the soil of oasis area in Basin belongs to the high fertility level, soil nitrogen variation is very large, the soil profile distribution type have surface gathering type?uniform type?bottom gathering type and oscillation type. The ammonium nitrogen accumulation coefficient in every soil profile and each layer are very close, that of shows uniform distribution, the nitrate nitrogen are mainly surface accumulation type and uniform type.(5) The nitrate nitrogen concentration of surface water has a tendency of increasing, The time series analysis of nitrate nitrogen concentration for phreatic water?confined water is exponential and polynomial type of rising trend respectively. The amount of nitrogen fertilizer application shows a linear increasing trend with about 7% annual growth rate in oasis agricultural areas, the amount of nitrogen fertilizer application shows a linear correlation with the nitrate nitrogen concentration, the correlation coefficient is 0.618. In accordance with the standard of groundwater quality in our country, the amount of nitrogen fertilizer applation should be less than 627.5kg·hm-2, according to the requirement of the standard for drinking water in our country, the amount of nitrogen fertilizer applation should be less than 377.5kg·hm-2. The predicted analysis gets the amount of nitrogen fertilizer applation in year of 2017?2030 are as high as 634.78kg·hm-2?984.74kg·hm-2 respectively, the nitrate nitrogen concentration of shallow groundwater almost add to 20.30mg·L-1?34.29mg·L-1. |
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