An assessment of the origin and variation of groundwater salinity in southeastern Ghana |
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| Authors: | Sandow Mark Yidana Adadow Yidana |
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| Institution: | (1) Department of Earth Science, University of Ghana, Box LG 58, Legon, Accra, Ghana;(2) Department of Community Medicine, School of Medicine and Allied Sciences, University for Development Studies, Tamale, Ghana |
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| Abstract: | Groundwater from the major aquifers in southeastern part of Ghana was sampled to determine the main controls on groundwater
salinity in the area. This paper uses multivariate statistical methods, conventional graphical methods and stable isotope
data to determine spatial relationships among groundwaters from the different hydrogeologic units in the area on the basis
of salinity. Q-mode hierarchical cluster analysis (HCA) was used to spatially classify the samples, whilst R-mode factor analysis
was used to reduce the dataset into two major principal components representing the sources of variation in the hydrochemistry.
Analysis of the major chemical parameters suggests that the principal component responsible for salinity increment in the
area is the weathering of minerals in the aquifers. This factor is especially more significant in the upland areas away from
the coast. The second factor responsible for salinity in the area is the combined effects of seawater intrusion, and anthropogenic
activities. This study finds that four major spatial groundwater groups exist in the area: low salinity, acidic groundwaters
which are mainly derived from the Birimian and Togo Series aquifers; low salinity, moderate to neutral pH groundwaters which
are mainly from the Voltaian, Buem and Cape Coast granitoids; very high salinity waters which are not suitable for most domestic
and irrigation purposes and are mainly from the Keta aquifers; and intermediate salinity groundwaters comprising groundwater
from the Keta basin aquifers with minor contributions from the other major terrains. The major water type identified in this
study is the Ca–Mg–HCO3 type, which degrades into predominantly Na–Cl–SO4 more saline groundwaters toward the coast. Stable isotope data analyses suggest that groundwater in the Voltaian aquifers
is largely of recent meteoric origin. The Birimian and Togo aquifers receive a component of recharge from the tributaries
of the Densu and Volta Rivers, after the waters have undergone evaporative enrichment of the heavier isotopes. In the Keta
basin, recharge is mainly from precipitation but an observed enrichment of 2H and 18O isotopes is probably due to seawater and evaporative effects since the water table there is very shallow. An analysis of
the irrigation quality of groundwater from the six aquifers in the study area using sodium adsorption ratio and electrical
conductivity suggests that most of the aquifers supply groundwater of acceptable quality for irrigation. The only exception
is the Keta Basin area, where extremely high salinities and SAR values render groundwater from this basin unsuitable for irrigation
purposes. |
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