广花盆地地下水化学特征及其演化分析

粤港澳大湾区(简称大湾区)建设已经上升为中国国家重大发展战略,水资源保障能力提升是大湾区建设的重点内容。城市应急备用水源建设是解决区内供水风险、保障特殊时期供水安全的重要手段,查明水环境质量状况及其演化对于备用水源地的科学建设意义重大。以粤港澳大湾区应急备用水源地-广花盆地为研究对象,采集并测试了41口监测井水样的常规化学组分,利用主成分分析、元素比值和Gibbs模型等多种方法,探讨了地下水主要离子来源及控制因子,评估了水质状况。结果表明:地下水的TDS变化范围为51.42-1 293.36 mg·L-1,Cl-为1.81-858.65 mg·L-1,淡水样占比95.1%,微咸水占比4.9%,反映地下水化学具有较大的空间差异;地下水阳离子以Ca2+和Na+为主,阴离子以HCO3-和Cl-为主,为HCO3-Ca、HCO3-Na·Ca、HCO3·SO4-Na·Ca和HCO3·Cl-Na·Ca型水;地下水的ρ(Na+)/ρ(Na++Ca2+)值为0.02-0.59,ρ(Cl-)/(Cl-+HCO3-)值为0.03-0.88,Ca/Na值为0.69-52.66,HCO3/Na值为1.28-41.64,据Gibbs模型和元素化学计量分析表明,其化学组成主要受含水层碳酸盐岩和硅酸盐岩风化控制;Na/Cl系数为0.31-6.39,局部地下水盐化明显,在北部高Cl-质量浓度区,其主要受古咸水与现代淡水混合影响,并有Na+与Ca2+离子交换,在南部的高Cl-质量浓度区,可能是海水沿流溪河咸潮上溯和河流侧向补给地下水所致;氨氮为0.05-7.50mg·L-1,有75.6%的样品超过Ⅲ类水标准,其主要来源为农业施肥、人畜粪便。由此,氨氮污染威胁地下水安全,作为应急备用水源应引起高度重视。

Hydrochemical Characteristic and Its Driving Force of Groundwater in the Covered Karst in Pearl River Basin

The development of Guangdong-Hong Kong-Macao Greater Bay Area will be a major priority project for the provincial government. The improvement of water resources guarantee capacity is the key content of this development strategy. The construction of urban emergency standby water source is important to solve the risk of water supply in this area and ensure the safety of water supply in a special period. It is of great significance for the scientific construction of the standby water source to check the quality and driving force of the aquatic environment. In this study, Guanghua basin, an important emergency standby water source in Guangzhou was selected as the research area. Forty-one monitoring wells in Guanghua Basin were sampled and monitored, and the main chemical components of groundwater are measured. The chemical characteristic of groundwater were measured by ion chromatography(ics-900). Multiple statistical methods, element ratio, and Gibbs model were used to analyze the chemical characteristics of groundwater and its main material sources in Guanghua basin, so as to provide a theoretical basis for groundwater quality evaluation and response to sudden pollution events. The results showed that the hydrochemical type was HCO3-Ca, HCO3-Na·Ca, HCO3·SO4-Na·Ca and HCO3·Cl-Na·Ca. The Na+/(Na++Ca2+) of water samples was 0.02–0.59, Cl-/(Cl-+HCO3-) was 0.03–0.88, Ca/Na was 0.69–52.66, HCO3/Na was 1.28–41.64, which suggested that the hydrochemical composition of the groundwater was mainly controlled by silicate rock and carbonatite weathering. The concentration of Cl-was in the range of 1.81–858.65 mg·L-1, and Na/Cl was 0.31–6.39, which suggested that some local groundwater is obviously salinized. This is mainly due to the mixing of ancient saltwater with modern freshwater in the north area. However, in the southern region, it may be caused by the upstream of seawater along the salt tide of Liuxi River and the invasion of saltwater. The concentrations of ammonia nitrogen were 0.05–7.50 mg·L-1 and 75.6% of the samples were higher than Class Ⅲ water standard, which mainly comes from agricultural fertilization, human and animal manure. Therefore, ammonia nitrogen pollution threatens the safety of groundwater. More attention should be paid to the emergency standby water due to this pollution.