唐山曹妃甸浅层地下水水化学特征及咸化成因

Hydrochemical characteristics and salinization causes of shallow groundwater in Caofeidian,Tangshan City

为了查明曹妃甸浅层地下水水化学及咸化成因,采集研究区河水、地下淡水、微咸水、咸水、卤水、雨水和海水等不同类型水样,对其水化学组成、离子比、Piper三线图、吉布斯图、氢氧同位素组成及14 C测年结果进行了分析。结果表明:(1)曹妃甸浅层地下水包括全新世沉积层潜水和晚更新世沉积层微承压水,且非原始封存在地层中而是形成于全新世中晚期。(2)地下潜水向海方向分布有淡水、微咸水、咸水水质类型,微承压水以咸水和卤水为主要水质类型;近冲洪积扇前缘水化学特征主要受岩石风化作用控制,围填海区及河口处水化学特征受海水混合作用控制,滨海平原区水化学特征主要受蒸发/结晶作用控制。(3)曹妃甸浅层地下水咸化过程主要是晚更新世以来海侵-海退时期形成海洋蒸发盐经大气降水和河水多期溶滤所致,其盐分来源于海水蒸发盐,河口及围填海区地下潜水盐分主要来源于现代海水入侵。

In order to find out the hydrochemical characteristics and salinization causes of shallow groundwater in Caofeidian area,we collected different types of water samples such as river water,underground fresh water,brackish water,salt water,brine,rainwater and seawater in the study area.We analyzed the chemical composition and ions ratio,Piper diagram,Gibbs diagram,hydrogen and oxygen isotope composition and14 C dating results of water samples.The results showed that the shallow groundwater included the phreatic water in the Holocene sedimentary layer and the faint confined water in the Late Pleistocene sedimentary layer,which were not originally enclosed in the strata but formed in the middle and late Holocene.The results also showed that there were freshwater,brackish water and salt water quality types for the phreatic water from alluvial fan to coastal plain and estuary.The salt water and brine are the main faint confined water quality types.Groundwater hydrochemistry in the frontal alluvial fan,reclamation area,and estuary and coastal plain are mainly controlled by rock weathering,seawater mixing,and evaporation/crystallization respectively.The salinization process of shallow groundwater in Caofeidian is mainly caused by repeated dissolution,by atmospheric precipitation and river water for many periods,of sea salt crystallized during the transgression and retreat period since the late Pleistocene.The salt in phreatic water of the estuary and reclamation area is mainly derived from modern seawater intrusion.