外来调水对华北低平原区地表水和地下水 水化学特征的影响* ——以河北省南皮县为例

华北低平原区有着巨大的粮食增产潜力,同时也是粮食生产和农业水资源矛盾突出的地区。外来调水与浅层微咸水的联合利用是解决区域水资源问题的有效途径之一,同时也将引起区域水循环和水环境的改变。为明确外来调水对华北低平原区地表水和地下水水化学特征的影响,本研究在华北低平原区河北省南皮县域内对调水后不同季节地表水和地下水进行调查和采样,利用水文地球化学和氢氧(d~2H、d~(18)O)稳定同位素相结合的方法,研究外来调水对地表水和地下水转化及其水化学特征的影响。研究结果表明,11月至翌年7月,受蒸发作用的影响,地表水电导率(EC)和钠吸附比(SAR)增加,d2H、d18O同位素不断富集;由于地表水和周围土壤的交换吸附作用使其水化学类型向Na~+、Cl~-和SO_4~(2-)增加、HCO_3~-减少的咸水转变。调水改变了地表水和浅层地下水之间的补给关系,11月至翌年3月,沟渠附近浅层地下水受外来调水直接或者灌溉补给,使得3月浅层地下水EC降低,埋深变浅,部分采样点分布在外来调水的SAR-EC区域。受调水影响,3月沟渠附近浅层地下水水化学类型为Na·Mg·Ca-Cl·SO_4、Na·Mg-Cl·SO_4·HCO_3、Na·Mg-SO_4·Cl·HCO_3等,是11月调水(Na·Mg·CaSO_4·HCO_3·Cl)和浅层地下水(Na·Mg-Cl·SO_4)的过渡类型。3月至7月浅层地下水补给沟渠水,地下水埋深变深,7月浅层地下水水化学类型与3月相似。调水可以季节性地改善区域内沟渠水及其附近的浅层地下水水质,而对深层地下水和坑塘水的水质无改善作用。调水对沟渠水水质的改善体现在调水季节,对浅层地下水水质的改善存在滞后性,2014年11月调水之后,2015年3月浅层地下水的水质得到改善。因此,采用调水和浅层地下水、坑塘水混合灌溉,对合理开发利用区域咸淡水资源以及深层地下水压采,恢复地下水位意义重大。

Effect of water diversion on hydro-chemical characteristics of surface water and groundwater in lowland area of the North China Plain: A case study of Nanpi County, Hebei Province

The great grain yield potential of the lowland area of North China Plain have been compromised by regional contradiction between water resources and agricultural production. The combined use of brackish shallow groundwater and diversion water is an effective way to address the regional water issue, which will certainly change the regional water cycle and environment. This study took different seasonal investigations in Nov. 2014, Mar. and Jun. in 2015 after water diversion in Nanpi County, which is located in the lowland area of North China Plain. The effects of water diversion on hydro-chemical characteristics of surface water and groundwater were determined using hydro-geochemical analysis and stable isotopes. The results showed that evaporation increased electrical conductivity (EC), sodium adsorption ratio (SAR) and enrichment of ²H and ¹⁸O isotopes in surface water. Soil sorption and exchange increased Na⁺, Cl^- and SO₄^-2, but decreased HCO3 in surface water, thereby increasing the water salinity in the region. Water diversion changed the interaction between surface water and groundwater. From November to March of the following year, diversion water recharged shallow groundwater near water division channels through directly percolation or irrigation. This decreased EC and depth of shallow groundwater at certain sampling points distributed along the diversion channel. In March 2015, the shallow groundwater types were Na·Mg·Ca-Cl·SO₄, Na·Mg-Cl·SO₄·HCO₃ and Na·Mg-SO₄·Cl·HCO₃, which was as a result of mixing of diversion water (Na·Mg·Ca-SO₄·HCO₃·Cl) with shallow groundwater (Na·Mg-Cl·SO₄) in November 2014. Shallow groundwater recharged channel water in March to July, which decreased groundwater depth. The shallow groundwater type in March was similar to that in July. Water diversion seasonally improved the quality of channel water and shallow groundwater in the vicinity. However, water diversion had no effect on deep groundwater and pool water quality. Water division improved channel water quality immediately after division. However, there was a time lag between diversion operation and shallow groundwater quality improvement. The quality of shallow groundwater improved in March 2015 due to water division in November 2014. Therefore, the combined use of shallow groundwater, division water and pool water for irrigation was critical for the rational development and utilization of both brackish water and freshwater resources, reduction of groundwater exploitation and recovery of deep groundwater level in the study area.