Freshwater lens oscillation induced by sea tides and variable rainfall at the uplifted atoll island of Minami-Daito, Japan

In order to evaluate the behavior of a freshwater lens in the uplifted atoll island of Minami-Daito, Japan, groundwater level and electrical conductivity were simultaneously measured in six monitoring wells. The monitoring allowed determination of the position and variability of the top and bottom p...

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Bibliographic Details
Published inHydrogeology journal Vol. 28; no. 6; pp. 2105 - 2114
Main Authors Yang, Heejun, Shimada, Jun, Shibata, Tomo, Okumura, Azusa, Pinti, Daniele L.
Format Journal Article
LanguageEnglish
Published Berlin/Heidelberg Springer Berlin Heidelberg 01.09.2020
Springer Nature B.V
Subjects
Aquatic Pollution
Atolls
Delay time
Diurnal
Earth and Environmental Science
Earth Sciences
Electrical conductivity
Electrical resistivity
Evaluation
Fresh water
Freshwater
Geology
Geophysics/Geodesy
Groundwater
Groundwater levels
Groundwater resources
Hydrogeology
Hydrology/Water Resources
Inland water environment
Lenses
Monitoring
Multiple regression analysis
Permeability
Rain
Rainfall
Regression analysis
Sediments
Tides
Waste Water Technology
Water Management
Water Pollution Control
Water Quality/Water Pollution
Japan
Island hydrology
Freshwater lens
Water sustainability
Japan
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Summary:In order to evaluate the behavior of a freshwater lens in the uplifted atoll island of Minami-Daito, Japan, groundwater level and electrical conductivity were simultaneously measured in six monitoring wells. The monitoring allowed determination of the position and variability of the top and bottom positions of the freshwater lens. The freshwater lens periodically oscillates with phase lags (delay time) every 3 h following sea tides. Recharge from local rainfall temporarily increases the volume of the freshwater lens but is disturbed by the low-permeability muddy sediments deposited on the central lowland of the island. Changes in the groundwater levels correlate well with rainfall, after first removing semi-diurnal, diurnal, and long-term components of the sea tides from the groundwater level data using a multiple regression analysis. Changes in the water electrical conductivity provide information on the temporal and spatial fluctuation of the freshwater lens. The monitoring scheme for this freshwater lens could be applied to other uplifted atolls, contributing to better evaluation of the potable groundwater resources and to making freshwater use sustainable on other islands.
ISSN:1431-2174
1435-0157
DOI:10.1007/s10040-020-02185-z