Hydrochemistry and quality of groundwater in alluvial aquifer of Karonga, Malawi

This study highlights the quality of groundwater for both drinking and irrigation in Karonga north where subsistence and commercial farming is practiced. All major groundwater quality descriptors and selected trace elements (iron, manganese, arsenic, and aluminum) were studied. The study demonstrated evidence of higher concentrations of bicarbonates (60–590 mg/L), total iron (2.2–5336 µg/L), total manganese (0.1–804 µg/L) and total arsenic (0.4–14.5 µg/L) in certain samples with low values of Eh (−32.0 to +25.8) and NO3− (≤8.2 mg/L) against WHO standards. Thirty-six percent of samples were rated as poor using the water quality index (WQI) criteria. No scaling potential was observed using the Langelier analysis. The majority of samples were of the mixed-bicarbonate type with the abundance order of cations as Ca2+ > Na+ > Mg2+ > K+. Carbonate dissolution, silicate weathering and cation exchange were identified as possible main geochemical control mechanisms. The sources responsible for fluoride and nitrate include anthropogenic activities and rock–water interaction. Dissolution/precipitation and pH control the levels of As, Fe and Mn.