Browsing by Author "Maloszewski, P."
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Item Estimating groundwater recharge from water isotope (δ2H, δ18) depth profiles in the Densu River basin, Ghana [Estimation de la recharge des eaux souterraines à partir des profils en profondeur des isotopes de l'eau (d2H, d18O) dans le bassin de la Rivière Densu, Ghana](Hydrological Sciences Journal, 2010) Adomako, D.; Maloszewski, P.; Stumpp, C.; Osae, S.; Akiti, T.T.Accurate estimation of groundwater recharge is essential for the proper management of aquifers. A study of water isotope (δ2H, δ18O) depth profiles was carried out to estimate groundwater recharge in the Densu River basin in Ghana, at three chosen observation sites that differ in their altitude, geology, climate and vegetation. Water isotopes and water contents were analysed with depth to determine water flow in the unsaturated zone. The measured data showed isotope enrichment in the pore water near the soil surface due to evaporation. Seasonal variations in the isotope signal of the pore water were also observed to a depth of 2.75 m. Below that depth, the seasonal variation of the isotope signal was attenuated due to diffusion/dispersion and low water flow velocities. Groundwater recharge rates were determined by numerical modelling of the unsaturated water flow and water isotope transport. Different groundwater recharge rates were computed at the three observation sites and were found to vary between 94 and 182 mm/year (± max. 7%). Further, the approximate peak-shift method was applied to give information about groundwater recharge rates. Although this simple method neglects variations in flow conditions and only considers advective transport, it yielded mean ground water recharge rates of 110-250 mm/year (± max. 30%), which were in the same order of magnitude as computed numerical modelling values. Integrating these site-specific groundwater recharge rates to the whole catchment indicates that more water is potentially renewed than consumed nowadays. With increases in population and irrigation, more clean water is required, and knowledge about groundwater recharge rates essential for improving the groundwater management in the Densu River basin can be easily obtained by measuring water isotope depth profiles and applying a simple peak-shift approach. © 2010 IAHS Press.Item Geochemical and isotopic studies of groundwater conditions in the Densu River Basin of Ghana(Environmental Earth Sciences, 2011-03) Adomako, D.; Osae, S.; Akiti, T.T.; Faye, S.; Maloszewski, P.The Densu River Basin (DRB) is an important agricultural area in Ghana and has a high population density. Water shortages have occurred in the basin due to drying out of surface water, heavy pollution and low yield in most of the production wells, which are crucial factors restricting sustainable socioeconomic development. This study was carried out to investigate the geochemical characteristics and evolution, as well as recharge processes in the DRB system with regard to the tectonics, geomorphology, lithology and flow system. It mainly used hydrochemistry, environmental isotopes and a series of comprehensive data interpretation, e. g., statistics, ionic ratios and Piper diagram to obtain a better understanding of the functioning of the system. The following hydrochemical processes were identified as the main factors controlling the water quality of the groundwater system: weathering of silicate minerals, dissolution, ion exchange and, to a lesser extent, evaporation, which seems to be more pronounced downgradient of the flow system. As groundwater flows from the recharge to discharge areas, chemical patterns evolve in the order of Ca2+-HCO3 -, Ca2+/Mg2+-HCO3 - to Ca2+/Na+-Cl-, Ca2+-Na+-HCO3 - and Na+-Cl- according to lithology. The environmental isotope (δ18O, δ2H, 3H) measurements further revealed that groundwater in the DRB was a relatively well-mixed system as evidenced by the encoded narrow range of values. However, deviation from the rainwater signature indicates combined local processes such as direct percolation through preferential channels, evaporation, and probable surface water and anthropogenic contribution to the system. © 2010 Springer-Verlag.