Assessment of Water Quality of Ndakaini Dam in Murang’a County, Kenya

Abstract

This study assessed the water quality in Ndakaini dam located in Murang‘a County to ascertain the physiochemical, biological levels as well as some selected heavy metal concentrations. Assessment was also done on some selected heavy metals in the Ndakaini dam sediment. Sampling was done during dry and wet seasons. Water samples were collected for analysis and the following selected parameters were analyzed; colour, taste, odour, turbidity, electrical conductivity, temperature, total solids, total alkalinity, total hardness, calcium hardness, pH, TDS, TSS, DO, COD, BOD, Si, sulphates, phosphates, chlorides, nitrates, fluorides, nitrites, total coliform and E. coli from some selected sites; dam Centre (C), Left edge (Eleft), right edge (Eright), Thika inlet River (TI), Kayuyu inlet (KI), Githika inlet (GI), Kiama River outlet (KO), Gituru outlet (GO) and Chania Outlet rivers (CO). In both seasons, the study findings showed that most of the physiochemical parameters in all sampling sites tested were within World Health Organization (WHO) and Kenyan Bureau of Standards (KEBS) permissible values except TSS, odour, colour and total coliform. The turbidity (in wet season) and colour levels exceeded WHO standards but are within KEBS standards. In both seasons, the total coliform (2.00 ±0.00 - 47.00±0.00 cfu/ml) values in all sampling sites did not meet WHO and KEBS limits of non-detectable standard. The biological results for the total coliforms and E. coli indicated that the dam was slightly polluted especially at Gituru Outlet (GO) site. When you consider COD and BOD values during dry season, values were higher compared to wet season. In both seasons, the dissolved oxygen (DO) was low at site KO with value of 5.86 mg/L in the dry season and 6.91 mg/L in the wet season. The selected heavy metals analyzed by Flame Atomic Absorption Spectroscopy in water and sediment samples were: Cu, Zn, Pb, Mn, Fe, Mn, Cd and Cr. Water sample result showed that the levels of Pb, Mn, Cr and Fe were higher than WHO guidelines and KEBS limit in most sampling sites. Across all sites, the extent of sediment quality pollution was mainly by Fe while Cu, Pb, Cr, Zn, Cd and Mn were within the recommended levels by the compared international sediment quality guideline used for this study. Statistical processing of data was performed using SPSS software and Microsoft Excel. There was strong correlation between turbidity with sulphate at r=0.945, colour with turbidity, TSS, sulphate and phosphate at (r=0.944), (r=0.761), (r=0.896) and (r=0.783) respectively in water samples. TDS correlated strongly with nitrate and nitrite at (r=0.962) and (r=0.950) respectively, fluoride with Zn and Pb at (r=0.810) and (r=0.753). The sources of pollution in Ndakaini dam catchment may be from the anthropogenic activities carried within the catchment like agricultural activities (farming and animal rearing), effluent discharges from nearby tea processing factories and domestic waste discharges as well.