Assessment of Seasonal Variation in Water Quality in River Rwizi Using Multivariate Statistical Techniques, Mbarara Municipality, Uganda

Assessment of seasonal variations

in surface water quality characteristics is an essential aspect for evaluating

water pollution due to both natural and anthropogenic influences on water

resources. In this study, temporal variations of water quality in river Rwizi

section within Mbarara municipality, Uganda, were assessed using multivariate

statistical methods. This river section is a major source of water for the

inhabitants of Mbarara municipality. Water samples from five sites were

analyzed for physicochemical parameters such as pH, EC, turbidity, temperature,

TSS, TDS, alkalinity, salinity, colour, NH3-N, , total hardness, BOD, COD,

DO, Ca, Mg, Fe, and Mn. About 50% of sites recorded colour above 800 Pt Co, 60%

of sites recorded turbidity above maximum permissible limit of 100 mg/l,

attributable to erosion and mineral matter. pH for dry season ranged between 6.5

and 8.5 whereas for rainy season was below 6.0. All study sites recorded total

Fe above 0.3 mg/l and Mn below 0.5 mg/l, attributable to chemical weathering of

host rock materials as well as from industrial effluent. About 60% of sites

recorded COD above 100 mg/l, 40% and 80% of study sites showed BOD above 50

mg/l in dry and rainy seasons respectively. Hardness ranged between 50 and 100

mg/l indicating that the water is moderately soft. Colour, turbidity,

alkalinity, TSS, TDS, salinity, pH, hardness, Fe, Mn, NH3-N, BOD,

COD, and DO were higher in rainy season, as a result of erosion, discharge of

domestic and industrial waste. Mg, Ca, and were

higher during dry season due to high evaporation of water from the river.

PCA/FA determined that 81.2% of the total variance was explained by the first

factor for the dry season and 69.2% for rain season. These results revealed

that water pollution resulted primarily from domestic waste water, agricultural

runoff and industrial effluents.