Working Document Series Open Access 2010 RUF-34619

Assessment of water quality in Mohale dam and associated rivers in Lesotho

M. JohanneR. MatingA.O. Olaleye

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Abstract

208 words

The study assessed Mohale dam and the associated rivers’ water quality over 5 years and comparing it to the water quality standards. It was believed that since this dam and the rivers occurred at elevations of between 2000m and 2900m above sea level, there was minimal anthropogenic pollution. Monthly data of the dam and the rivers water quality for the period 2003-2008 on pH, electrical conductivity (EC), potassium (K), sodium (Na), calcium (Ca), magnesium(Mg) and turbidity were collected from the Lesotho Highlands Authority (LHDA) database. In 2009 data for base cations (K, Na, Ca and Mg) and heavy metals (Fe, Cu, Zn, As and Pb) content were collected. The results showed that during the period 2003-2008, across sites and years, the pH and mean concentration of base cations were below the minimum permissible levels (mpl). However in 2009 Ca concentration had risen to values >200mg/ l while the levels of heavy metals, i.e., Fe, Cu and Zn were still lower than mpl, those of As and Pb were higher than mpl. The most important water quality variables differed across sites and, as such, their close monitoring is required in order to prevent their likely built up that may pose danger to health of the nation and associated countries.

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