密怀顺研究区地下水NO3--N时空变化分析

密怀顺地区是北京市重要的水源涵养区,直接影响着主城区的供水安全。2014年南水北调盈余水量通过潮白河河道回补地下水,地下水位不断抬升,使常年积累在耕地土壤中NO₃^--N对地下水环境风险不断增加。通过对地下水中NO₃^--N和耕地属性地块研究。结果表明:1)2015-2018年研究区地下水NO₃^--N浓度有升高趋势;2)2015-2018年研究区水质稳定区面积达到164.26km²,占比33.78%;其次为水质略变差区和水质变差区,面积分别为136.76km²和112.74km²,占比分别为28.12%和23.18%。3)耕地属性不变的7个有监测地块地下水NO₃^--N浓度均有不同程度升高,MW-3和MW-1地块超过地下水Ⅲ类水质标准;4)地下水NO₃^--N含量变化与地下水回补有一定关联。

Spatio-temporal variation of groundwater NO3--N in Miyun-Huairou-Shunyi recharge area

Miyun-Huairou-Shunyi recharge area is an important water conservation area in Beijing,which directly affects the safety of water supply in the main urban area.In 2014,the surplus water from the South-to-North Water Diversion project was used to recharge groundwater through the Chaobai River channel,and the groundwater level was constantly rising.As a result,the perennial accumulation of NO₃^--N in cultivated soil was increasing the risk to groundwater environment.So,the change of NO₃^--N in groundwater of this area needs to study.Our study shows that:(1)From 2015 to 2018,the concentration of NO₃^--N in local groundwater in the study area showed an increasing trend.(2)From 2015 to 2018,the water quality stability area of the study area reached 164.26km²,accounting for 33.78%of the total area.The water quality slightly worse zone is 136.76km²,and area of water quality deterioration zone is 112.74km²,accounting for 28.12%and 23.18%,respectively.(3)The concentration of NO₃^--N in groundwater of 7 monitored plots in cultivated land all increased in different degrees,and two plots surpassⅢgroundwater quality standards.(4)There is a certain correlation between the change of groundwater NO₃^--N content and groundwater recharge.