江苏滨海平原弱透水层封存的古咸水及其运移过程

李静; 张亚年; 梁杏; 刘彦

doi:10.19509/j.cnki.dzkq.2021.0158

江苏滨海平原弱透水层封存的古咸水及其运移过程

doi: 10.19509/j.cnki.dzkq.2021.0158

李静^1,,
张亚年²,
梁杏¹,
刘彦³

基金项目:

国家自然科学基金项目 41977167

国家自然科学基金项目 41502231

江苏省地质勘查基金项目苏国土资函[2014]842号

详细信息

作者简介:
李静(1985-), 女, 副教授, 主要从事水文地质学的教学与科研工作。E-mail: Jinglicug@163.com

中图分类号: P641
计量
- 文章访问数: 642
- PDF下载量: 43
- 被引次数: 0
出版历程
- 收稿日期: 2021-07-08
- 网络出版日期: 2022-03-02

Paleo-salt porewater trapped in the clayey aquitard and its transport processes in Jiangsu coastal plain

摘要

摘要: 滨海平原弱透水层广布且多赋存古咸水，其盐度分布及运移过程深刻影响着含水层地下水的演变，却得到甚少关注。采集了江苏滨海区7个浅层钻孔弱透水层原状样品，压榨法收集孔隙水。利用孔隙水天然示踪剂ρ（Cl^-），ρ（Br^-）剖面和数值模拟分析了弱透水层孔隙水盐度特征和运移机制。得出浅层孔隙水ρ（Cl^-）垂向剖面存在2个趋势：①峰值在表层，沿深度逐渐下降；②峰值在深度25m左右，向两端浓度降低。孔隙水ρ（Cl^-）为486.2~38 036.7 mg/L，Cl/Br比值为72~360（均值241）。ρ（Cl^-）与Cl/Br比值关系及剖面分布说明孔隙咸水为海相成因，来自于全新世海侵时期的古海水，并受到后期淡水的稀释。弱透水层孔隙水一维垂向运移数值模型表明海侵-海退事件控制了海岸带弱透水层孔隙水的盐度演变，全新世古海水仍封存在沉积物中，更新世时期的海水已被驱替。孔隙水运移以扩散为主，垂向运移速率为0.43~15.8 mm/Ma。在相对高渗透性的粉砂地层中，可能还受到侧向对流的影响。弱透水层中古海咸水的重新分布，尤其在地下水超采条件下，可能成为地下水的重要咸化来源。
- 弱透水层 /
- 孔隙水 /
- 滨海平原 /
- 咸化 /
- 运移
Abstract: Clayey aquitards are widespread in the coastal plain and they are capable to preserve paleo-saltwater. Its salinity distribution and transport process play an important role on the evolution of aquifer groundwater, yet they have attracted little attention. In this paper, undisturbed clayey samples in seven boreholes along the Jiangsu coastal plain were collected and porewater was extracted by squeezing. Based on the natural tracers Cl^- and Br^- profiles and numerical simulation, porewater salinity characterization and transport mechanism were analyzed. The results showed that two trends of porewater Cl^- variations are observed: one is that Cl^- peak value is near surface and decreases with depth; the other one is that the Cl^- peak value is at depth of 25 m and decreases towards both ends. Porewater has a Cl^- range of 486.2-38 036.7 mg/L and Cl/Br of 72-360(average: 241). The relations between Cl^- and Cl/Br ratios and the profile signature indicate that saline porewater is of marine origin, and from the Holocene transgression seawater. Subsequently, they were diluted by freshwater. Aquitard porewater 1-D transport model suggests that the transgression and regression events are dominant for the salinity evolution. Holocene seawater is still trapped in the sediment whereas Pleistocene seawater has been flushed out. In aquitard, diffusion is dominant for solute transport with the vertical velocity of 0.43-15.8 mm/yr and influenced by advection in higher permeability sand layers. The redistribution of paleo-saltwater, in particular, in the condition of groundwater over-extraction, would be the important saline source for aquifer groundwater.
- aquitard /
- porewater /
- coastal plain /
- salinization /
- transport

HTML全文

图 1 研究区地理位置(a)与江苏滨海钻孔位置(b)(海岸线的演变参考文献[26])

Figure 1. Location of the study area (a) and the borehole location in the Jiangsu coastal area (b)

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图 2 研究钻孔的岩性柱状图

Figure 2. Lithological column of the studied boreholes

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图 3 理论模型中海相弱透水层孔隙水垂向运移过程

a.弱透水层厚度10 m; b.弱透水层厚度20 m; c.不同厚度弱透水层中点孔隙水浓度的时间变化

Figure 3. Vertical transport process of porewater in marine aquitard in a theoretical model

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图 4 中国东部滨海区弱透水层孔隙水Cl^-浓度垂向剖面(SY1钻孔数据引自文献[7]; G1数据引自文献[33]; LZ12数据未发表)

Figure 4. Porewater Cl^- vertical profiles of aquita in the east coastal area of China

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图 5 弱透水层孔隙水ρ(Br^-) 与ρ(Cl^-)(a)和Cl/Br与ρ(Cl^-)(b)关系图

Figure 5. Relationship between Br^- and Cl^- (a), Cl/Br and Cl^- (b) in the aquitard porewater

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图 6 江苏滨海J1、J4和SY1孔模拟与实测ρ(Cl^-)剖面

Figure 6. Simulated Cl data and measured ones for J1, J4 and SY1 boreholes in the Jiangsu coastal area

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表 1 孔隙水运移模型中介质参数和运移时间设计

Table 1. Medium parameters and transport time design of porewater transport model

	模拟条件a			模拟条件b			模拟条件c
弱透水层厚度/m	10			20			5，10，15，20，30，50
渗透系数K/(m·s^-1)	1×10^-10	1×10^-9	1×10^-8	1×10^-10	1×10^-9	1×10^-8	1×10^-10
运移时间/ka	1，2，5						5~0
扩散系数D_e/(m²·s^-1)	4.5×10^-10
上、下边界	定浓度100 mg/L

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表 2 一维垂向对流-扩散模型的参数及边界条件

Table 2. Parameters and boundary conditions in the 1-D advective-diffusion flow model

钻孔	模拟深度/m	运移时间/a		渗透系数 K/(m· s^-1)	扩散系数 D_e/(m²·s^-1)	上边界：定浓度(g/L)	下边界	海相沉积层厚度/m
钻孔	模拟深度/m	T₁	T₂	渗透系数 K/(m· s^-1)	扩散系数 D_e/(m²·s^-1)	上边界：定浓度(g/L)	下边界	海相沉积层厚度/m
J1	30	8 000	800	3.4×10^-10	4×10^-10	T1:19；T2:23	流出边界	2~14
J4	50	8 000	500	0~20：7.5×10^-9	7×10^-10	T1:16；T2:0.1		4~18
J4	50	8 000	500	20~50：1.3×10^-9	7×10^-10	T1:16；T2:0.1		4~18
SY1	60	8 000	300	0~20：1.2×10^-8	5×10^-10	T1:19；T2:0.1		10~25
				20~60：6.2×10^-10	2.3×10^-10			10~25

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