Description
Groundwater is a critical resource for sustaining domestic, agricultural, and industrial activities in the Komadugu-Yobe Basin (KYB). However, growing pressures from over-exploitation, rapid population growth, pollution from geogenic and anthropogenic sources, and climate variability threaten the long-term sustainability of this vital water source. This thesis employs an integrated approach which combines geochemical modelling, hydrochemical characterization, Geographic Information System (GIS)-based techniques, chemometric analysis, index-based models and environmental stable isotopes analysis to determine the factors influencing groundwater chemistry, recharge mechanisms, and contamination sources, human health risk of heavy metals in KYB, to support Integrated Water Resources Management (IWRM) and help in achieving Sustainable Development Goal 6 (SDG 6) in KYB and the wider Sahel region. Groundwater samples were collected from 240 water points across Komadugu-Yobe basin during two sampling campaigns (120 each) of wet and dry seasons. The pH, temperature, total dissolved solids (TDS), oxidation reduction potential (ORP), and electrical conductivity (EC) were assessed in situ using a handheld digital electrical conductivity meter in situ while dissolved oxygen (DO) was measured using DO meter. Major cations (Na, Ca, Mg, and K) and heavy metals (As, Cd, Cu, Zn, Pb, Ni, Fe, Mn, Cr and Co), were analyzed using inductively coupled plasma optical emission spectroscopy (ICPOES) while anions (Cl, HCO3, NO3, and SO4) were analyzed using ion chromatography (IC). Total alkalinity and bicarbonate were measured in situ using a HACH digital alkalinity kit by the titrimetric method and in Laboratory using KONE equipment. The stable isotopes of δ2H and δ18O were analysed at IAEA Isotope laboratory, Vienna and Isotope Laboratory for the Ministry of Water in Lilongwe, Malawi using Picaro Stable Isotope Analyser.Hydrochemical analysis revealed that groundwater in Komadugu-Yobe basin is predominantly of Ca-Mg-HCO₃ water type, constituting about 59 % of the samples. Some groundwater quality parameters exceeded World Health Organization guidelines for drinking water, while Gibbs diagrams identified rock-water interactions as primary factor influencing the groundwater chemistry. The groundwater quality index (GWQI) classified 63 % of samples as excellent and 27% as good for drinking. The study showed a strong interaction between geology, hydrochemistry and groundwater quality during wet season. A further geochemical and chemometric analysis revealed that chloride and nitrate originated from anthropogenic sources mainly synthetic fertilizers and nitrification processes in pit latrines. Principal Component Analysis (PCA) indicated that the groundwater chemistry is primarily influenced by geogenic processes, agricultural activities, industrial processes and mineral weathering. Additionally, hierarchical cluster analysis (HCA) identified the impacts of evaporation and ion exchange processes within the aquifer systems. Groundwater sampled during wet and dry seasons is significantly undersaturated with calcite, dolomite and fluorite minerals and partial pressure of carbon dioxide (pCO2) exceeded the atmospheric pCO2 in nearly all samples.
The study also assessed heavy metal pollution and their associated human health risk, highlighting lead, iron, manganese, and cadmium as the main contaminant and pose significant health risks to the local communities in the basin. Index-based models revealed that the groundwater is less polluted in upstream parts and highly polluted in downstream parts of the basin. Human health risk assessments showed that both adults and children are at risk of both carcinogenic and noncarcinogenic health effects from drinking contaminated groundwater. Chemometric analysis suggests that physicochemical parameters and heavy metals likely have different geochemical behaviours and originated from distinct geogenic and anthropogenic sources. Moreover, isotopic analysis of δ¹⁸O and δ²H signatures provided insights into groundwater recharge, indicating that local precipitation is the primary source of recharge particularly in areas near Hadejia-Nguru wetland, Hadejia Komadugu Valley, Chalawa George Dam, and Tiga Dam, with seasonal variations in isotopic signatures due to evaporative enrichment before infiltration. The local meteoric water line (LMWL) was defined as δ2H = 6.7 (± 0.1) δ18O + 4.1 (±0.4) for the KYB, while regional analyses of δ¹⁸O and δ²H signatures revealed the influence of the Inter-Tropical Convergence Zone (ITCZ) on isotopic variability. D-excess results highlighted complex recharge processes in both sedimentary and basement aquifers, suggesting that recharge occurs primarily during periods of heavy rainfall with depleted isotopic signatures. D-excess analysis suggests that average precipitation in the entire Sahel region exhibits a general continental effect until the ITCZ meets the Congo Basin and that average precipitation in the entire Sahel region occurs under equilibrium condition. The findings from this study are essential for policymakers, stakeholders, government agencies, NGOs, and local communities for implementing integrated water resources management strategies and toward achieving SDG 6 in Komadugu-Yobe basin and the wider Sahel region.
| Period | 6 Feb 2025 |
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| Examinee | Abdulrahman Shuaibu |
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| Degree of Recognition | National |