北京西南近郊包气带和渗流场对地下水中硝酸盐氮的影响

Influence of aeration zone and flow field on groundwater nitrate nitrogen in southwest suburb of Beijing

为了研究北京西南近郊地表污染物通过包气带后进入地下水中以及其受地下水流场的影响,利用Hydrus软件建立不同位置包气带数值模型,研究不同地层条件下初始浓度为30 mg·L^(-1)的高硝酸盐氮废水在包气带中的迁移规律,分析各模拟点位在50、100、200、300、400、500 d时硝酸盐氮浓度随地层深度变化特征,以及各模拟点包气带底部硝酸盐氮浓度随时间变化特征。分析结果显示:北京市西南近郊4个模拟点包气带对硝酸盐氮拦截率分别为5.93%、10.69%、15.87%、33.83%,表明研究区从西向东包气带对地下水的防护作用由弱变强,结合研究区多年硝酸盐氮超标范围、多点位硝酸盐氮浓度多年监测数据和第四系地下水水位及补给径流条件,可知地下水中硝酸盐氮迁移变化受地下水流场影响较大,根据研究区实际提出了预防该区域硝酸盐氮污染进一步加重的管理建议。

This paper focuses on the amount of nitrate nitrogen of the surface pollutants entering groundwater after passing through vadose zone and its influence by groundwater flow field in the southwest suburb of Beijing.Based on the numerical simulation of vadose zone at different locations in that area,it studies the migration law of wastewater with initial concentration of 30 mg·L^(-1) nitrate nitrogen in vadose zone under different stratum conditions.The nitrate nitrogen concentration changes are analyzed on the 50th,100th,200th,300th,400th and 500th day at each simulation point,which shows that the nitrate nitrogen concentration at the bottom of vadose zone at each simulation point changes with time.The interception rates of nitrate nitrogen in the aeration zone at the four simulated sites were 5.93%,10.69%,15.87%and 33.83%,respectively,indicating that the protective effect of the aeration zone on groundwater from west to east in the study area changes from weak to strong.Combined with the over-standard range of nitrate nitrogen in the study area for years,the quaternary groundwater level and recharge runoff conditions,this paper presents the influencing factors of nitrate nitrogen in the groundwater and puts forward proposals to prevent nitrate nitrogen pollution from further aggravating.