广西防城港地区浅层地下水pH值时空分布、成因及对生态环境的影响

【研究目的】查明防城港地区浅层偏酸性地下水时空分布、成因及环境影响。【研究方法】于2013—2015年间进行了浅层地下水pH值现场测试，枯水期214组，丰水期168组；讨论了其时空分布特征、成因和生态影响。【研究结果】结果表明，丰水期和枯水期偏酸性（pH <6.5）地下水样分别占79.3%和64.3%，pH值总体上丰水期低于枯水期。地下水pH值在低山区（均在5≤pH＜5.5范围，平均值5.18，n=4）＜丘陵区（大多数5≤pH＜6.5，平均值5.18，n=202）＜平原区（大多数6.5≤pH＜8.5，平均值6.77，n=8）。【结论】偏酸性地下水成因主要与偏酸性大气降水有关，其次与酸性的包气带介质及硫化物矿物的氧化有关。偏酸性大气降水入渗补给是丰水期pH值低于枯水期的主要原因。相比较而言，潮汐作用使得江平地区地下水pH值升高。偏酸性地下水影响饮水安全（研究区枯水期仅20.6%的样品pH值符合生活饮用水标准），促进某些有害组分的释放，腐蚀地下管网和建筑桩基等设施。偏酸性地下水向地表水排泄亦可对地表水环境和地表生态系统产生影响。本研究有助于研究区水资源管理。创新点：本研究利用地质调查项目数据优势，系统阐述了防城港地区浅层偏酸性地下水时空分布特征；偏酸性地下水的成因与偏酸性大气降水、酸性包气带介质和硫化物矿物氧化有关；偏酸性地下水对人类健康、地下设施和生态环境具有潜在影响。

Spatial-temporal distribution, genesis and environmental impact of the shallow groundwater pH values in the Fangchenggang, Guangxi

This paper is the result of hydrogeological survey engineering.Objective] The purpose of this study is to uncover the spatial-temporal distribution, genesis, and environmental impacts of shallow acidic groundwater in the Fangchenggang area.Methods] In-situ pH values of shallow groundwater were determined in the study area during 2013 to 2015, including 214 samples in the dry season and 168 samples in the wet season. Spatial and temporal distribution, genesis, and ecological influences of the pH values were discussed.Results] Results show that the acidic groundwater samples (pH < 6.5) account for 79.3% and 64.3%, respectively, in the wet and dry seasons. In general, pH values in the wet season are lower than in the dry season. Values are generally lower in the low mountain areas (pH 5.0-5.5, mean 5.18, n=4) relative to the hillys (pH mostly 5.0- 6.5, mean 5.97, n=202), and the plain areas (pH typically 6.5- 8.5, mean 6.77, n=8).Conclusions] Occurrence of acidic shallow groundwater can be contributed primarily to the acid rain, and partly to the acidic unsaturated zone, and oxidation of sulfide minerals. Accordingly, seasonal changes of acidic rain should principally responsible for the spatial variations of groundwater pHs. By contrast, however, tides could increase groundwater pH values in the Jiangping area. Acidic groundwater threatens safe drinking water supply, because only 20.6% samples in the dry season having pHs within the drinking water standard thresholds. Also, it may promote release of some harmful elements from aquifer sediments, and erode underground pipe networks and building pile foundations. In addition, due to discharge, acidic groundwater could influence surface water environment and surface ecosystems. This study contributes to water resources management in the study area.Highlights: Base on the advantages of geological survey data, this study uncovers the spatial- temporal distribution of acidic shallow groundwater in the Fangchenggang area. In general, occurrence of acidic shallow groundwater can be contributed to the acid rain, acidic unsaturated zone, and oxidation of sulfide minerals. Finally, the possible impacts of acidic groundwater on the ecological environment were identified.