珠江三角洲浅层地下水pH值的分布及成因浅析

Characteristics and preliminary analyses of the formation of pH in shallow groundwater in the Pearl River delta

通过珠江三角洲地区两千余组地下水样的pH值现场测试,发现水体酸化是该区地下水环境最为突出的问题之一。偏酸性地下水的分布范围占全区76.3%。该区地下水pH值的分布具有明显的区域性特征。丘陵台地区以偏酸性地下水为主,pH值集中在5.6～6.4;三角洲平原区地下水普遍呈中性,pH值主要介于6.4～7.2。丰、枯水期地下水pH值变幅不大,受酸雨影响,丰水期略有降低。该地区影响地下水pH值的主要因素为酸雨、包气带介质、河流及海水潮汐。丘陵区酸雨入渗强度大、包气带的缓冲能力低,对地下水pH值偏低起了主要作用;平原区粘土层厚,酸雨入渗强度减弱,而河流与地下水交换频繁,加上咸潮与海水入侵的影响,共同导致了地下水pH值升高。

More than 2,000 groundwater samples were detected in situ for pH in the Pearl River Delta.The results show that water acidification is the most prominent problem in the groundwater environment.Acidic groundwater accounts for 76.3% of the total area.Distribution of pH in the shallow groundwater is of obvious regional characteristics.In the hilly areas,pH in groundwater ranges mostly from 5.6 to 6.4,while pH varies mainly between 6.4 and 7.2 in the plain regions.Due to the influence of acid rain,pH of groundwater is slightly lower in wet season than in dry season.It is considered that acid rain and medium buffer of unsaturated zone play an important role in the lower pH value in groundwater in the hilly areas.In the plain areas,the acid rainfall infiltration coefficient becomes lower,while rivers and seawater tide are the dominant factors causing higher pH values of the groundwater.