Seasonally Variant Stable Isotope Baseline Characterisation of Malawi’s Shire River Basin to Support Integrated Water Resources Management

Abstract

Integrated Water Resources Management (IWRM) is vital to the future of Malawi and motivates this study’s provision of the first stable isotope baseline characterization of the Shire River Basin (SRB). The SRB drains much of Southern Malawi and receives the sole outflow of Lake Malawi whose catchment extends over much of Central and Northern Malawi (and Tanzania and Mozambique). Stable isotope (283) and hydrochemical (150) samples were collected in 2017–2018 and analysed at Malawi’s recently commissioned National Isotopes Laboratory. Distinct surface water dry-season isotope enrichment and wet-season depletion are shown with minor retention of enriched signatures ascribed to Lake Malawi influences. Isotopic signatures corroborate that wet-season river flows mostly arise from local precipitation, with dry-season flows supported by increased groundwater contributions. Groundwater signatures follow a local meteoric water line of limited spread suggesting recharge by local precipitation predominantly during the peak months of the wet-season. Relatively few dry-season groundwater samples displayed evaporative enrichment, although isotopic seasonality was more pronounced in the lowlands compared to uplands ascribed to amplified climatic effects. These signatures serve as isotopic diagnostic tools that valuably informed a basin conceptual model build and, going forward, may inform key identified Malawian IWRM concerns. The isotopic baseline establishes a benchmark against which future influences from land use, climate change and water mixing often inherent to IWRM schemes may be forensically assessed. It thereby enables both source-water protection and achievement of Sustainable Development Goal 6.

National Stable Isotope Baseline for Precipitation in Malawi to Underpin Integrated Water Resources Management

“…The latter process may also impact near-surface groundwater resources, especially in Malawi's semi-arid lowlands. The use of isotopic tools underpinned by the isotopic precipitation characterization herein is already beginning to provide insight into such processes, as demonstrated in our recent basin- [39] and catchment-scale studies [40].…”

“…This study represents the first-ever characterization of the stable isotope precipitation baseline for Malawi and hence provides a pivotal step to achieving the long-held ambition to provide isotope-informed IWRM for the country. Study findings have already helped underpin our companion catchment [39] and basin-scale [40], stable-isotope studies in Malawi and ongoing studies of other catchments.…”

Attainment of water and sanitation goals: a review and agenda for research

“…Four articles had been published in the journal “Water” and obtained 18 citations. The articles in “Water” dealt with groundwater vulnerability (Addison et al, 2020a , b ), integrated water resource management (Banda et al, 2019 ; Banda et al, 2020 ), and stranded asset-based investment strategies for SDG 6 (Kalin et al, 2019 ); three articles are on Applied Science-Basel and got six citations. The articles in this journal focused on focusing on sustainable rural water supply (Leborgne et al, 2021 ), groundwater salinity and rural water supply challenges (Rivett et al, 2020 ), and Human and health implications of Fluoride content in groundwater (Addison et al, 2020a , b ), one article on Sustainability are without any citations.…”

Paleo-Geohydrology of Lake Chilwa, Malawi is the Source of Localised Groundwater Salinity and Rural Water Supply Challenges

“…Lake Chilwa closure corresponding to the 631 m lake contour outline occurred in relatively recent times, probably within the last 15,000 years (15 ka) [47,50]. Sediment dating of the Chilwa-Chiuta sandbar with depth indicates a range of ages for lake high-stand phases of 44-33, 26-21 and 18-12 ka [7].…”

“…Samples were collected in dedicated amber bottles for analysis of deuterium and oxygen-18 ratios at IAEA and CJF supported Malawi Government's Isotope Hydrology Laboratory (IHL). Analytical methods used have been recently reported by Banda et al [46,47].…”