莱州湾沿岸寿光、莱州和龙口地下水的稳定同位素与地球化学
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国家自然科学基金项目(面上项目,重点项目,重大项目)


Hydrogeochemistry and Stable Isotopes of Groundwater from Shouguang, Laizhou and Longkou in the South Coast Aquifer of Laizhou Bay
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    摘要:

    依据地下水咸化机理:蒸发、溶解和混合,海水入侵是地下淡水与较之更咸的海水的混合,海水和淡水的混合包括水分子的混合和溶解盐分的混合。只有溶剂水分子和溶质溶解盐分都发生了相同比例的混合,才能确定二种水体发生了混合。地下淡水变咸并不能都归因于海水入侵,也有可能源于蒸发或溶解。鉴定是否存在海水入侵可运用惰性示踪剂和反应示踪剂来共同识别。惰性示踪剂包括δD、δ18O、Cl-和Br-,反应示踪剂包括主要化学成分和微量元素。本研究对莱州湾沿岸寿光、莱州和龙口的地下水进行了化学成分形成过程的对比研究。莱州采集样品6件,龙口10件,寿光9件。莱州和龙口的碎屑沉积物以硅酸盐矿物为主,而寿光的沉积物来源于南部鲁中南山地的碳酸盐岩。根据莱州采样点地理条件和样品的稳定同位素δD δ18O分布域确定了当地降雨入渗的多年平均值,进而明确龙口样品也源于就地降雨入渗补给,根据高程效应和当地水文情况确定寿光样品补给来自南部山区的降水,经河道排入洼地后入渗地下。Cl- δ18O关系表明盐分都来源于淡水溶解的蒸发盐,而非与海水混合。Br-/Cl-比值证实了蒸发盐溶解,还存在人为污染物和海侵沉积物中有机质分解的影响。从三线图可看出龙口样品经历了离子交换反应。主要成分和微量元素(HCO3-, H2SiO3, F-, Li+, Sr2+和Ba2+)的含量与样品所处含水层的矿物组成有关,反映出水岩作用。所有样品都没有淡水和海水混合的现象。惰性示踪剂分析提供了区域地下水补给的框架,明确了大气水源因溶解蒸发盐而咸化,排除了淡水和海水混合的可能性。用反应示踪剂中主要化学成分和微量元素来分析水中化学成分的形成过程,在和海洋盐分输入对比基础上,二者偏差值主要源自水-岩相互作用结果,包括溶解、沉淀、离子交换等,以及局部样品的污染物输入。所以沿海地带研究地下水咸化,先要解决溶剂的混合问题,在此基础上辅以水文地球化学分析,利用水化学的多种示踪剂,主要解决溶质混合以及盐分来源问题。

    Abstract:

    Groundwater salinization is attributed either to evaporation, dissolution or mixing. Seawater intrusion falls into the latter, i.e. mixture of fresh groundwater and seawater, which implies this mixture occurs not only in the dissloved salts but also in water molecules. To confirm the occurrence of mixing, it is important to make sure that both the solvent and solute have undergone the same degree of mixing. Note that besides seawater intrusion, fresh groundwater salinization may also be attributed to evaporation and (or) dissolution. In this study, by employing both the inert (δD, δ18O, Cl- and Br-) and reactive (major and minor elements) tracers, we analyzed these chemistry data of groundwater samples collected in Laizhou Bay to identify seawater intrusion. Samples were collected from coastal aquifer of south Laizhou Bay, including 6 in Laizhou city, 10 in Longkou and 9 in Shouguang. The sediments of Laizhou and Longkou mainly consist of silicate clasts, while Shouguang is mostly covered by carboantes, which are supposed to be supplied from the southern mountainous area. By stable isotopic analyses (δD and δ18O) combining the local geographical conditions in Laizhou, the groundwater samples due to precipitation recharge were determined. We next confirmed that the groundwater samples in Longkou is also directly recharged from local precipitation, whereas for Shouguang, based on the altitude effect and the local hydrological setting, we infer the groundwater is probably recharged from the precipitation of southern mountainous area. Cl- δ18O relation indicates that salinity is originated from the dissolution of evaporite by freshwater, rather than mixing with seawater. Br-/Cl- ratios confirmed the dissolution of evaporite, and it can also reflect the influence of man made pollutants and decomposition of organic matter in transgressive sediments. As reflected by the piper digram, the Longkou samples have undergone ion exchange reactions, and ion (HCO3-, H2SiO3, F-, Li+, Sr2+ and Ba2+) concentrations, which relate to the aquifer mineral composition, also reflect extensive water rock interaction. All samples are not indicatative of mixture of fresh water and sea water. Inert tracer analyses provide a framework for regional groundwater recharge, determine that the salinization of atmosphere water is due to evaporites dissolution, and also exclude the possibility of freshwater and seawater mixing. By comparing the element concentration ratios of groundwater and marine ratios, the deviation can be explained by water rock interaction, including dissolution, precipitation, ion exchange, and contaminants enter of local samples. Therefore, for groundwater salinization study in coastal zone, the first step is to determine the possibility of solvent mixing, which is followed by identifing the solute mixing and salt sources, using various chemical tracers.

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杨巧凤,王瑞久,徐素宁,李文鹏,王志一,梅军军,丁志磊,杨培杰.2016.莱州湾沿岸寿光、莱州和龙口地下水的稳定同位素与地球化学[J].地质学报,90(4):801-817.
YANG Qiaofeng, WANG Ruijiu, XU Suning, LI Wenpeng, WANG Zhiyi, MEI Junjun, DING Zhilei, YANG Peijie.2016. Hydrogeochemistry and Stable Isotopes of Groundwater from Shouguang, Laizhou and Longkou in the South Coast Aquifer of Laizhou Bay[J]. Acta Geologica Sinica,90(4):801-817.

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  • 收稿日期:2015-09-19
  • 最后修改日期:2015-12-08
  • 录用日期:2016-03-14
  • 在线发布日期: 2016-04-26
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