华北山前平原典型站点地下水位与硝酸盐变化特征

Characteristics of groundwater level and nitrate variability at typical sites in the Piedmont Region of the North China Plain

华北平原是我国重要的集约化农业生产区,该区域农业生产长期以来依赖于过度开采地下水以及过量施肥,造成地下水位持续下降和地下水水质恶化,严重威胁区域生态环境安全、粮食安全和人民健康。本文利用长期观测资料分析了华北山前平原井灌区典型站点(中国科学院栾城农业生态系统试验站)的浅层地下水水位埋深和水质长期变化特征。研究发现:1)在1974—2019年,地下水位呈下降趋势,46年内下降了32.6 m,年均下降速率0.7 m·a^(−1);随着地下水超采综合治理的持续开展,2020—2022年地下水位有回升的趋势,平均回升速率为0.2 m·a^(−1)。2)浅层地下水的电导率在年内存在较大波动(425~776μS·cm^(−1)),表明农业灌溉地下水开采导致了深层地下水(电导率较低、水质相对较好)与浅层地下水(电导率较高、水质相对较差)在年内发生了多次且剧烈的混合。3)近20年的定位观测数据表明,浅层地下水水质呈现变差的趋势,其中氯离子和硝酸根离子的浓度升高。本研究对于该地区合理利用地下水资源,促进地下水水质保护具有重要的科学价值。

The North China Plain is an important agricultural production area.Agricultural production in this region has depended on the overexploitation of groundwater and overfertilization,resulting in a continuous decline in the groundwater level and deterioration of groundwater quality,which seriously threatens the safety of the regional ecosystem,food security,and public health.In this study,using a set of long-term observations at a typical site(Luancheng Agro-Ecosystem Experimental Station of Chinese Academy of Sciences)in the Piedmont Plain of the North China Plain,we analyzed the characteristics of interannual changes in shallow groundwater depth and water quality.The results indicated that:1)The groundwater level exhibited a decreasing trend,dropping 32.6 m from 1974 to 2019,with an average annual decline rate of 0.7 m·a^(−1).By the recent comprehensive management of groundwater overdraft,the groundwater level has recovered as a result of an increased rate of 0.2 m·a^(−1)in the last three years(2020−2022).2)The electrical conductivity of shallow groundwater fluctuated considerably within the year,ranging from 425μS∙cm^(−1)to 776μS∙cm^(−1),indicating that groundwater exploitation for agricultural irrigation resulted in intense mixing between deep groundwater(with lower electrical conductivity and relatively better water quality)and shallow groundwater(with higher electrical conductivity and relatively poorer water quality)within the year.3)The water quality observation data for the past 20 years indicated a trend of deterioration in the shallow groundwater quality,with elevated concentrations of chloride and nitrate ions.This study is of great scientific value for the sustainable utilization of groundwater resources and promotion of groundwater quality protection in the region.