Abstract
Hidden hot springs likely impact rural water supplies in Malawi’s Rift Valley with excess dissolved fluoride leading to localised endemic severe dental fluorosis. Predicting their occurrence is a challenge; Malawi’s groundwater data archive is sporadic and incomplete which prevents the application of standard modelling techniques. A creative alternative method to predict hidden hot spring locations was developed using a synthesis of proxy indicators (geological, geochemical, dental) and is shown to be at least 75% effective. An exciting collaboration between geoscientists and dentists allowed corroboration of severe dental fluorosis with hydrogeological vulnerability. Thirteen hidden hot springs were identified based on synthesised proxy indicators. A vulnerability prediction map for the region was developed and is the first of its kind in Malawi. It allows improved groundwater fluoride prediction in Malawi’s rift basin which hosts the majority of hot springs. Moreover, it allows dentists to recognise geological control over community oral health. Collaborative efforts have proven mutually beneficial, allowing both disciplines to conduct targeted research to improve community wellbeing and health and inform policy development in their respective areas. This work contributes globally in developing nations where incomplete groundwater data and vulnerability to groundwater contamination from hydrothermal fluoride exist in tandem.
Highlights
Hot springs are known globally for high groundwater fluoride concentrations [1,2,3,4]
Hot springs are linked to localised endemic severe dental fluorosis due to elevated fluoride concentrations from hydrothermal groundwater contaminating rural drinking water supplies
We coin the term ‘hidden hot springs’ to describe hot springs which do not occur at the surface as springs per se, but rather are buried beneath the unconsolidated sediments of Malawi’s rift basin discharging hydrothermal water from depth to shallow groundwater
Summary
Hot springs are known globally for high groundwater fluoride concentrations [1,2,3,4]. Hot springs arise from discharge of hydrothermal groundwater at the Earth’s surface and are often associated with pools of steaming hot water, discharging gas bubbles, sulphurous smells, mineral encrustations, and extremophile bacteria. Hot springs are usually located in increased numbers where the Earth’s crust is thinnest, rift valleys where tectonic plates are moving apart (rifting). The primary concern is the vulnerability of drinking water and potential health impacts of ‘Hidden hot springs’—a term coined to describe the circumstance whereby hydrothermal groundwater from depth fails to discharge directly at ground surface as a spring per se, but rather discharges into groundwater at the sediment base of the rift basin and is buried beneath sediments and hidden from view. Hidden hot springs may result in hydrothermal fluoride-rich groundwater mixing with shallow groundwater and contamination of rural community water supply
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