PhD Examination

Description

Isotope hydrology and hydrogeochemistry of surface water and groundwater in the Lake Malawi basin to support sustainable water resource management

This thesis presents groundbreaking body of research aimed at examining meteoric water inputs and their interactions with surface water and groundwater systems to enhance understanding of Lake Malawi basin’s hydrological processes to provide transformative insights into the basin's water cycle. This was achieved through an innovative multi-method approach that integrated stable isotopic and hydrogeochemical tracers. The thesis adopted an integrated-holistic methodological framework that considered precipitation, groundwater and surface water as interconnected systems in the basin’s water cycle. The aim and objectives of the research were achieved through a series of scientific publications, forming a significant body of research with critical implications. The thesis successfully established a baseline forstable isotopes in precipitation, a fundamental benchmark for future isotopic studies in Malawi and the wider region. This foundational isotopic baseline provided groundbreaking isotopic insights into Malawi’s water cycle by establishing a pioneering Local Meteoric Water Line, consistent with the Global Meteoric Water Line. The thesis revealed predominant oceanic influences and continental influences marked by moisture recycling likely from the African Great Lakes large scale evaporation effect and seasonal shifts in the Intertropical Convergence Zone. The thesis provided increased and unique insights into origin of groundwater and geochemical evolution dynamics within the Lake Malawi basin aquifer systems. The thesis demonstrates primary influence of non-evaporated modern precipitation on groundwater recharge, initiating critical geochemical reactions with host rock minerals upon infiltration into the subsurface zone. The rock mineral-water reactions release essential ionic species and form secondary minerals, with sodium and calcium ions being predominant cations, thereby influencing groundwater chemistry. Through geochemical modelling insights, the thesis clarified that groundwater evolution is dominated by silicate dissolution reactions, highlighting critical relationships between meteoric water inputs, evaporative processes, and spatial and seasonal variations in groundwater hydrochemistry. The thesis further revealed distinct hydrogeochemical signatures and widespread nitrate occurrence, underscoring potential human impacts on groundwater quality. The thesis established a basin-scale isotopic and hydrochemical baseline characterization of surface water system using deuterium, oxygen-18, deuterium, and major ionic tracers. It showed that surface water flows are influenced by non-evaporated modern precipitation and groundwater baseflow, with distinct seasonal variability. Riverine flows exhibited greater isotopic variability than lakes and reservoirs, with wet season depleted signals at higher elevations and dry season enriched signals in lowlands. The convergence of highland-plateau and rift margin river systems resulted in isotopic depletion within escarpment zones and progressive enrichment through lakeshore flood plains. The thesis highlighted the significant contribution of local precipitation to surface water flows and the retention of enrichment signals in lakes due to high residence time. The thesis aligns with Malawi's water policy, the Water Resources Act, and the Malawi 2063 Development Agenda, advocating for expanded monitoring networks, cross-disciplinary collaborations, and community engagement. It also supports the objectives of the GloWAL Network, IWAVE, GNIP, and GNIR, emphasizing regional collaboration and comprehensive data collection. Overall, this thesis provides new and unique knowledge critical for advancing the understanding of the hydrological cycle of the Lake Malawi basin. It serves as a call to action for sustainable water management in Malawi, stressing the importance of innovative, integrated, and participatory approaches. The thesis outcomes are expected to inform and guide development of sustainable water resource management strategies, aligning with objectives of Sustainable Development Goal (SDG) 6 and Integrated Water Resource Management (IWRM) practices. Overall, this thesis delivers a new and unique body of research with critical policy and scholarly implications.

Period	28 Feb 2025
Examinee	Limbikani Banda
Examination held at	University of Strathclyde
Degree of Recognition	National