Spatial and Seasonal Variation of Selected Water Quality Parameters in Chania River Catchment, Kenya

Abstract

River systems in Kenya have been under threat from anthropogenic based pollution for a long time. River Chania which originates from the Aberdare Ranges and flows through highly productive agricultural land towards Thika town is one of these rivers. It is the only source of water for Thika town and parts of Machakos County. Non-point pollution from agricultural lands and point pollution resulting from settlement have led to water quality degradation in the river. The aim of this study was to investigate water quality in River Chania, assess types of pollution from the catchment and propose mitigation measures. Water sampling and analysis was done in accordance with the standard methods of the American water works association and statistical packages used for statistical analysis. Sampling was done in both wet and dry seasons and on seven different locations along a selected stretch of the river. Physical parameters were determined onsite using portable meters while anions; SO42-, NO3--N, NO2--N, PO43- and Cl- were determined using spectrophotometric methods. Metals analyzed were; Na, K, Ca, Mg, Mn, Fe, Zn, Cu, Pb and Cd using Atomic absorption spectrophotometer. Turbidity was the highest recorded parameter during the wet season with a mean of 169.4 NTU and its strong correlation with 75% of the parameters (Pearson’s r>0.5) meant that farming in the upper catchment had an effect on nitrate and phosphate among others leaching into the river during the wet season. In summary, 45% of the parameters showed significant seasonal variation (p<0.5) with mean concentration of 50% of the parameters being higher during the dry season. Turbidity, nitrate, nitrite, manganese, iron and lead exceeded WHO guidelines indicating poor water quality in the catchment. As domestic and industrial waste water contribute to point pollution downstream, unsustainable farming practices give rise to significant nonpoint pollution upstream of the river. The study recommends strict enforcement of environmental laws to curb point pollution and an incentive based approach to reduce non-point pollution with public enlightenment on how to control anthropogenic activities.