WANG Weiqiang,WANG Ya,KUANG Xingxing,et al.Hydrochemistry and numerical simulation of pore water solute of the Quaternary aquitard in the Pearl River Delta[J].Acta Scientiarum Naturalium Universitatis Sunyatseni,2023,62(01):44-56.
WANG Weiqiang,WANG Ya,KUANG Xingxing,et al.Hydrochemistry and numerical simulation of pore water solute of the Quaternary aquitard in the Pearl River Delta[J].Acta Scientiarum Naturalium Universitatis Sunyatseni,2023,62(01):44-56. DOI: 10.13471/j.cnki.acta.snus.2021D063.
Hydrochemistry and numerical simulation of pore water solute of the Quaternary aquitard in the Pearl River Delta
The Quaternary aquitard of the Pearl River Delta (PRD) overlies the basal confined aquifer, and its hydrogeochemical evolution process has a decisive influence on the basal aquifer. In order to understand the formation and evolution of pore water in the aquitard of the Pearl River Delta, this study analyzes the major ions (K
+
,Na
+
,Ca
2+
、Mg
2+
,Cl
-
,SO
4
2-
,Br
-
), hydrogeochemical parameters and mineral saturation index of pore water samples of the ZK01 borehole drilled in Zhongshan City. The results show that the salinity of pore water is relatively high and the TDS is between 4.42 and 30.47 g/L. The water chemistry of pore water is generally Cl-Na type, which is similar to seawater, and the concentrations of major ions tend to increase with the borehole depth. The Cl/Br,
γ
(Na/Cl) coefficients and Gibbs analysis show that the salinity of the aquitard pore water is mainly originated from seawater, and probably originated from Holocene seawater. Concentration of SO4
2-
is mainly controlled by sulfate reduction in the aquitard and not affected by the precipitation of gypsum. Ca
2+
and Na
+
in shallow pore water are affected by cation exchange,which causes Na
+
depletion and Ca
2+
enrichment. NH
4
+
mainly exchanges with Mg
2+
,resulting in the increase of NH
4
+
in pore water. K
+
is mainly controlled by mixing and adsorption during pore water evolution, showing depletion characteristics. Based on the
14
C dating data and taking the sedimentary environments, processes and rates under consideration, an one-dimensional solute transport model of the aquitard Cl
-
was established by using the hydrogeochemical simulation software PHREEQC. The simulation results show that the effective diffusion coefficient of the aquitard is about 6.0×10
-11
m
2
/s,the vertical convection velocity can be neglected, and diffusion is the key mechanism for vertical solute transport in the PRD Quaternary aquitard.
关键词
珠江三角洲弱透水层孔隙水化学溶质运移
Keywords
the Pearl River Deltaaquitardpore water chemistrysolute transport
HENDRY M J, WASSENAAR L I. Controls on the distribution of major ions in pore waters of a thick surficial aquitard[J].Water Resources Research,2000,36(2): 503-513.
LI J,LIANG X,IN M,et al.Geochemical signature of aquitard pore water and its paleo-environment implications in Caofeidian Harbor,China[J].Geochemical Journal,2013,47(1):37-50.
LIU Y,MA T,CHEN J,et al.Contribution of clay-aquitard to aquifer iron concentrations and water quality[J].Science of the Total Environment,2020,741:1-11.
KUANG X X,JIAO J J,LIU K.Numerical studies of vertical Cl-, δ2H and δ18O profiles in the aquifer-aquitard system in the Pearl River Delta,China[J].Hydrological Processes,2015,29(19):4199-4209.
KUANG X X,JIAO J J,WANG Y.Chloride as tracer of solute transport in the aquifer-aquitard system in the Pearl River Delta,China[J].Hydrogeology Journal, 2016,24(5):1121-1132.
HAN D M,CAO G L,CURRELL M J,et al. Groundwater salinization and flushing during glacial‐interglacial cycles: Insights from aquitard porewater tracer profiles in the North China plain[J].Water Resources Research,2020,56(11):1-23.
JIAO J J,WANG Y,CHERRY J A,et al.Abnormally high ammonium of natural origin in a coastal aquifer-aquitard system in the Pearl River Delta,China[J]. Environmental Science & Technology,2010,44(19): 7470-7475.
WANG Y, JIAO J J, CHERRY J A,et al.Contribution of the aquitard to the regional groundwater hydrochemistry of the underlying confined aquifer in the Pearl River Delta,China[J].Science of the Total Environment,2013,461:663-671.
ZONG Y Q,HUANG G,SWITZER A D,et al.An evolutionary model for the Holocene formation of the Pearl River delta,China[J].The Holocene,2009,19(1):129-142.
ZONG Y Q,YIM W W S,YU F, et al.Late Quaternary environmental changes in the Pearl River mouth region,China[J].Quaternary International,2009,206(1/2):35-45.
WEI X,WU C Y.Holocene delta evolution and sequence stratigraphy of the Pearl River Delta in South China[J].Science China Earth Sciences,2011,54(10):1523-1541.
WANG Y.Isotopic and hydrogeochemical studies of the coast aquifer-aquitard system in the Pearl River Delta,China[D].Hong Kong:The University of Hong Kong,2011.
KWONG H T,JIAO J J,LIU K,et al.Geochemical signature of pore water from core samples and its implications on the origin of saline pore water in Cangzhou, North China Plain[J].Journal of Geochemical Exploration,2015,157:143-152.
GIBBS R J.Mechanisms controlling world water chemistry[J].Science,1970,170(3962):1088-1090.
APPELO C A J, POSTMA D. Geochemistry,groundwater and pollution[M].USA:CRC Press,2004.
WANG Y, JIAO J J.Origin of groundwater salinity and hydrogeochemical processes in the confined Quaternary aquifer of the Pearl River Delta,China[J]. Journal of Hydrology,2012,438:112-124.
蓝先洪.珠江三角洲晚第四纪沉积物的有机地球化学特征[J].热带海洋,1991(1):13-20.
支兵发.珠江三角洲平原高铵地下水的形成演化[J].安全与环境工程, 2015,22(4):1-9.
WANG Y,JIAO J J,CHERRY J A.Occurrence and geochemical behavior of arsenic in a coastal aquifer-aquitard system of the Pearl River Delta,China[J]. Science of the Total Environment,2012,427: 286-297.
PARKHURST D L,APPELO C A J.Description of input and examples for PHREEQC version 3: A computer program for speciation,batch-reaction,one-dimensional transport,and inverse geochemical calculations[R].US Geological Survey,2013.
ZHENG C M, BENNETT G D.Applied contaminant transport modeling[M].New York:Wiley-Interscience,2002.
WANG X S,JIAO J J,WANG Y,et al.Accumulation and transport of ammonium in aquitards in the Pearl River Delta(China) in the last 10 000 years: Conceptual and numerical models[J].Hydrogeology Journal, 2013,21(5):961-976.
TIMMS W A,HENDRY M J.Quantifying the impact of cation exchange on long-term solute transport in a clay-rich aquitard[J].Journal of Hydrology,2007, 332(1/2):110-122.