Study Of The Origin Of Salinity In The Unsaturated Soil Zone Using Chloride Profiles And Stable Isotope At Ekumfi Akwakrom And Ekumfi Asokwa Mankessim Municipality Of The Central Region Of Ghana

Abstract

This research was carried out to investigate the origin of salinity in the unsaturated soil zone with emphasis on chloride profile and stale isotopes in the Ekumfi Akwakrom and Ekumfi Asokwa in Mankessim Municipality of the Central Region of Ghana, which has been reported to have high saline groundwaters. A total of 159 samples were analysed, which comprises: fifty – six (56) rainwater samples, fifty – three (53) soil from the unsaturated zone, two (2) groundwaters, forty – two (42) water extracted from soil and six (6) water from unsaturated zone. Samples of soil, rainwater, groundwater and water from unsaturated zone were analysed for physical parameters, major ions, trace elements, nutrients and stable isotopes composition. Chloride concentrations varied as the depth increases along the profile, showing accumulation of Cl in the unsaturated zone at depth of 80 cm and 120 cm. Stable isotope of the rainwater, water extracted from soil, water from unsaturated zone and groundwater in the study area indicates that, rainfall is the only source of recharge to the groundwater in the area. The chloride mass balance (CMB) approach was used to estimate recharge rate in the flushed portion of profiles in the study area and is 65.56 mm/yr., (mean for 9 profiles), any heavy/intense rainfall can result in downward movement of salts that had accumulated near the surface of the soil. The high chloride concentration found in groundwaters in the coastal aquifers is as a result of dissolution of soluble salts ( ) accumulated in the unsaturated zone at a depth of 80 .0 cm and 120.0 cm and not direct sea water intrusion. Movement of water through the unsaturated zone dissolves these salts without any isotopic fractionation and discharges them into the groundwater system leading to groundwater salinization in the study area.