Developing countries such as Malawi require improved access to isotope tracer tools to better characterize and manage water resources threatened by land development, deforestation and climate change. This is the first published study to use an isotope facility developed in Malawi for this purpose, instead of relying upon sample analyses from abroad. Results from this new facility are used to evaluate an important Lake Malawi catchment in the Rift Valley. This work successfully established a stable-isotope baseline, hydrochemical signatures, and system conceptualization against which future policy change and management strategies may be measured. Precipitation isotopic composition was consistent with the Global Meteoric Water Line, but varied, confirming different precipitation systems nationally. Groundwater largely followed a Local Meteoric Water Line, with limited isotopic variation indicating predominant areal groundwater recharge, but with dry-season evaporative enrichment of groundwater near Lake Malawi. Surface-water isotopes widely varied with local precipitation, suggesting the latter accounted for wet-season river flows, but upstream dambo (complex wetlands occupying a shallow, seasonal waterlogged depression) helped sustain dry-season flows. Isotope capacity reinforced water-resource conceptualization and provenance in a hydrologically complex, but not atypical, Rift Valley system, exhibiting a noted complexity of groundwater–surface-water interactions. The latter, critical to integrated water resource management, requires more focused study, to which an expanded array of isotopes will contribute to tracking Sustainable Development Goal 6 targets. This study and future catchment studies should help underpin Malawian water-resource policy implementation on several identified fronts.
Fluoride concentrations in Malawi’s groundwater are primarily controlled by geogenic sources that are highly variable and may cause a heterogeneous fluoride occurrence and local-to-regional variations in fluorosis health risks posed. Our aim was to address the challenge of developing a national solution to predicting groundwater vulnerability to geogenic fluoride risk in the country of Malawi where incidences of fluorosis are reported and typical developing world problems of limited data and resources abound. Previously there have only been sporadic, local-scale studies linking fluoride occurrence with health risks in Malawi with no attempts to tackle the issue nationally. We hence develop a screening method for predicting groundwater vulnerability to geogenic fluoride in the form of detailed risk maps developed from statistical relationships shown between groundwater fluoride occurrence and known geogenic fluoride sources. The approach provides for dynamic update and informed acquisition of new data and hence on-going improving capacity to manage fluoride risks in Malawi. Our screening method provides a technical basis for redefining national fluoride policy to ensure commensurate management of health risks posed. Specifically, the approach provides a pathway for stepped progression from the current 6 mg/L Malawian standard for fluoride in drinking water to adoption of the World Health Organisation 1.5 mg/L guideline standard.
Consumption of groundwater containing fluoride exceeding World Health Organization (WHO) 1.5 mg/L standard leaves people vulnerable to fluorosis: a vulnerability not well characterised in Malawi. To evaluate geogenic fluoride source and concentration, groundwater fluoride and geology was documented in central Malawi where groundwater supplies are mainly sourced from the weathered basement aquifer. Lithological composition was shown as the main control on fluoride occurrence. Augen gneiss of granitic composition posed the greatest geological fluoride risk. The weathered basement aquifer profile was the main factor controlling fluoride distributions. These results and fluoride-lithology statistical analysis allowed the development of a graded map of geological fluoride risk. A direct link to human health risk (dental fluorosis) from geological fluoride was quantified to support science-led policy change for fluoride in rural drinking water in Malawi. Hazard quotient (HQ) values were calculated and assigned to specific water points, depending on user age group; in this case, 74% of children under six were shown to be vulnerable to dental fluorosis. Results are contrary to current standard for fluoride in Malawi groundwater of 6 mg/L, highlighting the need for policy change. Detailed policy recommendations are presented based on the results of this study.
Despite an estimated 90,000 groundwater points, mostly hand-pumped boreholes, being used for drinking-water supply in Malawi, evaluation of groundwater arsenic has been limited. Here we review the literature and collate archive data on groundwater arsenic occurrence in Malawi; add to these data, by surveying occurrence in handpumped boreholes in susceptible aquifers; and, conclude on risks to water supply. Published literature is sparse with two of the three studies reporting arsenic data in passing, with concentrations below detection limits. The third study of 25 alluvial aquifer boreholes found arsenic mostly at 1-10 μg/l concentration, but with four sites above the World Health Organisation (WHO) 10 μg/l drinking-water guideline, up to 15 μg/l; the study also discerned hydrochemical controls. Archive data from non-governmental organisation (NGO) borehole testing (two datasets) exhibited below detection results. Our surveys in 2014-18 of hand-pumped supplies in alluvial and bedrock aquifers tested 310 groundwater sites (78% alluvial, 22% bedrock) and found below test-kit detection (<10 μg/l) arsenic throughout, except possible traces at two boreholes containing geothermal-groundwater contributions. Our subsequent survey of 15 geothermal groundwater boreholes/springs found four sites with arsenic detected at 4-12 μg/l concentration. These sites displayed the highest temperatures, supporting increased arsenic being related to a geothermal groundwater influence. Our 919 sample dataset overall indicates arsenic in Malawian groundwater appears low, and well within Malawi's drinking-water standard of 50 μg/l (MS733:2005). Still, however, troublesome concentrations above the WHO drinking-water guideline occur. Continued research is needed to confirm that human-health risks are low; including, increased monitoring of the great many hand-pumped supplies, and assessing hydro-biogeochemical controls on the higher arsenic concentrations found.
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