Seasonal assessment of water quality and major ion chemistry in the lower region of Lake Kariba, Zambia

Abstract

Lake Kariba is a major freshwater resource in Southern Africa that sustains livelihoods, biodiversity, and regional economic activities, yet faces pressures from land-use practices and climate variability. This study assessed the effects of surrounding land use on lake water chemistry, with emphasis on anions, cations, and key nutrients. Fifty-three water samples were collected from downstream sites during hot-dry, cool-dry, and rainy seasons to capture temporal variability. Ionic composition and potential sources were determined using Ion Chromatography and Inductively Coupled Plasma techniques. Dominant ions, including Mg (3.3–3.9 mg L⁻¹), SO₄²⁻ (> 2 mg L⁻¹), Cl⁻ (1.2–1.6 mg L⁻¹), and Si (> 4 mg L⁻¹), remained relatively stable across seasons. Parameters such as pH, F⁻ SO₄²⁻, Cl⁻, TDS, EC, and temperature exhibited greater seasonal variability, with significant differences (p < 0.05) associated with land-use activities. Areas influenced by aquaculture and agricultural activities showed comparatively elevated nutrient concentrations relative to sites dominated by natural vegetation. Although localized impacts were evident, the Water Quality Index (13.1–13.6) consistently classified the water as excellent. Overall, the lake maintains good water quality, but continued monitoring and targeted management are necessary to address land-use pressures and safeguard its ecological integrity.