Characterization of groundwater quality in Small Island developing states (SIDS): a case study in the island of Mauritius.

Abstract

This thesis presents a systematic investigation of groundwater systems in Mauritius through three interconnected studies examining temporal patterns, climate impacts, and flow dynamics. The research addresses the knowledge gaps regarding groundwater vulnerability in Small Island Developing States (SIDS) while developing a framework for sustainable resource management. The temporal analysis spanning 2010-2021 revealed significant trends in groundwater quality across Mauritius's five major aquifers (Aquifer I: Curepipe-Vacoas-Flic en Flac; Aquifer II: Phoenix-Beau Bassin-Albion-Moka-Coromandel; Aquifer III: Nouvelle France-Rose Belle- Plaisance; Aquifer IV: Nouvelle Découverte-Plaine des Roches-Midlands-Trou d'Eau Douce; and Aquifer V: Northern Aquifer). Conductivity showed decreasing trends in four aquifers (- 0.09 to -0.40 μS/cm per month), while pH demonstrated significant changes in Aquifers II and V. Total Dissolved Solids decreased notably in Aquifers I and II (-0.12 and -0.18 units/month respectively), indicating spatially variable water quality evolution. The investigation of climate impacts revealed generally weak correlations between groundwater quality and climate indices. The 12-month Standardized Precipitation Index showed strongest correlations with sulphate in Aquifers II and III (r = -0.40 and -0.33), while global climate modes demonstrated minimal influence. Analysis of Cyclone Esami (January 2020) indicated short-term impacts on water quality parameters, though data limitations prevented a complete statistical analysis of extreme event impacts. Isotopic analysis conducted during 2022-2023 using 67 boreholes across all five aquifer systems revealed distinct spatial and temporal patterns in groundwater composition. Results showed δ2H values ranging from -22.8per mil to -5.6per mil and δ18O values from -4.2per mil to -1.56per mil, with systematic variations corresponding to elevation and aquifer characteristics. Inter-aquifer connectivity was evident between Aquifers I and II, while Aquifer V showed clear evidence of marine influence with elevated chloride concentrations (42 mg/L) and enriched isotopic signatures in coastal areas. The research provides a framework for assessing groundwater vulnerability in SIDS through integration of temporal trend analysis, climate correlation studies, and isotopic characterization. Key findings include the importance of spatial heterogeneity in system response, the primacy of local hydrogeological conditions over regional climate patterns, and the need for spatially targeted management approaches. These insights enable development of evidence-based strategies for sustainable groundwater management in SIDS contexts.