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Hydrogeochemical properties of a salinity-affected coastal aquifer in western Japan

Hiroshiro, Y ; Jinno, K and Berndtsson, Ronny LU (2006) In Hydrological Processes 20(6). p.1425-1435
Abstract
Coastal groundwater aquifers are often exposed to heavy pumping and consequently to risks of saltwater intrusion. In many cases, however, the observed increase in groundwater salinity can only be partly explained by actual saltwater intrusion from the sea. Other salinity-increasing processes may also significantly contribute to the total salt content of the groundwater. This paper describes a geochemical investigation that was carried out to investigate recent salinity increases in groundwater for the Motooka coastal area in Fukuoka, Japan. A strong increase in electrical conductivity at 15-20 m depth was observed, corresponding to the freshwater and saltwater interface. Oxidation-reduction potentials observed in deeper groundwater were... (More)
Coastal groundwater aquifers are often exposed to heavy pumping and consequently to risks of saltwater intrusion. In many cases, however, the observed increase in groundwater salinity can only be partly explained by actual saltwater intrusion from the sea. Other salinity-increasing processes may also significantly contribute to the total salt content of the groundwater. This paper describes a geochemical investigation that was carried out to investigate recent salinity increases in groundwater for the Motooka coastal area in Fukuoka, Japan. A strong increase in electrical conductivity at 15-20 m depth was observed, corresponding to the freshwater and saltwater interface. Oxidation-reduction potentials observed in deeper groundwater were low, indicating long residence time for the groundwater. These results, together with hydrogen-oxygen isotope ratio analysis, indicated that the deeper groundwater is affected by seawater. Consequently, observed tritium concentration in the shallow groundwater system was higher than that of the deeper groundwater system, and a C-14 isotope dating of shell samples collected at 2 m depth indicated an age of about 2000 years. The overall results suggest that the aquifer was originally below the current sea floor and that deeper saline groundwater is not mixed with the shallower fresh groundwater. The deeper groundwater is, therefore, mainly affected by old seawater. In other words, modern saltwater intrusion has not yet occurred even if some wells contain saline water. The study shows that, even though coastal aquifers are heavily pumped, the reason for the rise in groundwater salinity may not necessarily be due to seawater intrusion. Further geochemical and hydrological investigations will be necessary to identify the underlying mechanisms. Copyright (c) 2006 John Wiley & Sons, Ltd. (Less)
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author
; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
environmental isotope, analysis, electrical conductivity, redox conditions, salinity-affected coastal groundwater aquifer, groundwater quality
in
Hydrological Processes
volume
20
issue
6
pages
1425 - 1435
publisher
John Wiley and Sons
external identifiers
  • wos:000237015200013
  • scopus:33646145501
ISSN
1099-1085
DOI
10.1002/hyp.6099
language
English
LU publication?
yes
id
04317ca0-b312-441f-8535-427f41132f86 (old id 411193)
date added to LUP
2016-04-01 11:50:21
date last changed
2021-01-10 03:35:32
@article{04317ca0-b312-441f-8535-427f41132f86,
  abstract     = {Coastal groundwater aquifers are often exposed to heavy pumping and consequently to risks of saltwater intrusion. In many cases, however, the observed increase in groundwater salinity can only be partly explained by actual saltwater intrusion from the sea. Other salinity-increasing processes may also significantly contribute to the total salt content of the groundwater. This paper describes a geochemical investigation that was carried out to investigate recent salinity increases in groundwater for the Motooka coastal area in Fukuoka, Japan. A strong increase in electrical conductivity at 15-20 m depth was observed, corresponding to the freshwater and saltwater interface. Oxidation-reduction potentials observed in deeper groundwater were low, indicating long residence time for the groundwater. These results, together with hydrogen-oxygen isotope ratio analysis, indicated that the deeper groundwater is affected by seawater. Consequently, observed tritium concentration in the shallow groundwater system was higher than that of the deeper groundwater system, and a C-14 isotope dating of shell samples collected at 2 m depth indicated an age of about 2000 years. The overall results suggest that the aquifer was originally below the current sea floor and that deeper saline groundwater is not mixed with the shallower fresh groundwater. The deeper groundwater is, therefore, mainly affected by old seawater. In other words, modern saltwater intrusion has not yet occurred even if some wells contain saline water. The study shows that, even though coastal aquifers are heavily pumped, the reason for the rise in groundwater salinity may not necessarily be due to seawater intrusion. Further geochemical and hydrological investigations will be necessary to identify the underlying mechanisms. Copyright (c) 2006 John Wiley & Sons, Ltd.},
  author       = {Hiroshiro, Y and Jinno, K and Berndtsson, Ronny},
  issn         = {1099-1085},
  language     = {eng},
  number       = {6},
  pages        = {1425--1435},
  publisher    = {John Wiley and Sons},
  series       = {Hydrological Processes},
  title        = {Hydrogeochemical properties of a salinity-affected coastal aquifer in western Japan},
  url          = {http://dx.doi.org/10.1002/hyp.6099},
  doi          = {10.1002/hyp.6099},
  volume       = {20},
  year         = {2006},
}