HYDROGEOCHEMICAL AND WATER QUALITY ASSESSMENT IN KAYELEKERA, NORTHERN MALAWI

Abstract

Kayelekera communities depend on rivers as main source of water supply for industrial, domestic, and agricultural use. In this study, samples were collected in both rainy and dry season followed by an assessment on the state of water quality and hydro-geochemical processes controlling river water chemistry using statistical and geochemical modelling methods in Kayelekera. Hierarchical Cluster Analysis classified water samples into three distinct clusters (C1-C3) in both seasons. One - way ANOVA (p<0.05) and paired T test (p<0.05) showed significant difference among the samples and, between the seasons respectively, indicating variation of water chemical composition. PCA results revealed that chemical composition in C1 was dominated by SO4 2-, U and K in rainy season while pH, Cl-, and U dominated C1 in dry season, C2 and C3 were dominated by HCO3-and SO42-inrainy season while, in dry season, C2 was dominated by Ca2+, Mg2+, Na+, Fe, Si, HCO3-and SO42-, and C3 negatively correlated with major ions. Further, water type results indicate C1 (mixed cation-HCO3-), C2 (Ca- HCO3--SO42-) and C3 (Ca-Mg- HCO3 -) characteristics in rainy season while, in dry season, shows C1 (mixed cation- HCO3--Cl-), C2 (Ca-HCO3-) and C3 (Ca-Mg- HCO3-). Normalized Na+/ HCO3-and Mg2+ /Ca2+ molar ratios suggest dominance of silicate weathering and mixing of silicate and carbonate weathering products controlling river water chemistry. Inverse models and SI results revealed main reactions as dissolution of calcite, plagioclase, biotite, feldspars with carbon dioxide and pyrite consumption; kaolinite, iron (III) hydroxides and quartz. High NO3−/Na+and SO42-/Cl- molar ratios were recognized in C2 and C3 samples in both seasons respectively, showing impact of anthropogenic activities from agricultural and industrial sources. Uranium levels in river water attributed to presence of uranium minerals, however,uranium speciate into Ca2UO2(CO3)3 and UO2(CO3)22-. Consequently, all samples were within WHO guidelines for major chemical constituents except pH and Fe in some samples.