Effects of industries and other land use systems on the water Quality within the Nairobi river sub-catchments, Kenya.

Abstract

This thesis examines water quality status and deterioration in the Upper- Athi-Nairobi sub-catchments which covers an area of 1154.4 km2 with an annual discharge rate of 99242 m3/year (9.9 X 104 m3/yr). It is based on field and laboratory analysis of water quality parameters. The subject matter includes the assessment of land use processes responsible for water quality deterioration. These include Industrial and Agricultural activities. The study demonstrates how useful industrial (manufacturing) and agricultural (irrigation) activities are to the water quality deterioration for different uses. No detailed work of this kind has been carried out in Kenya so far and certainly not in the Nairobi river sub-catchments. Water samples were collected from the two distinctive land use activities and analysed for the different water quality parameters, notably heavy metals and pesticides. Heavy metals especially Mercury and Lead were found to' have high concentrations above the critical WHOand the Kenya standards [Mercury =0.03 and Lead =0.1 mg/L]. Other elements with harmful effects to Human health such as Fluoride and Nitrate were found to have concentrations surpassing the required WHOand keriya standards. Fluoride was measured at 2.5 rngZL and Nitrate at 0.5 mg/litre (L). Pesticide residues in water notably DDT, "Ambush" ,"Ridomil", "Malathion" etc were all found to surpass the WHOand Kenya standards for drinking water. DDT was measured at 0.000086 mg/L "Ambush" 0.1413 mgZL, "Ridomil" 0.147 rngZL, "Malathion"0.00039 mg/L. Their variations in mass loadings per day are represented in table 48. , xi Generally water quality was found to deteriorate from one river to another in respect to the landuse activities at its proximity. Their rates of deterioration were also found to vary. Ngong River exhibited the highest water quality deterioration with a rate of 0.42 at Embakasi, followed by Nairobi River at Dandora with a rate of 0.39. Kamiti River and Kasarani had the least rates of rt<.. deterioration. This were well depicted in figure 13. These corresponded or conformed well with the land use activities along their water courses. Water pollutants were also found to vary with time (season) from one river course to another. CODand BODdemonstrated a time persistence nature for most rivers and the same with TDS. These again showed close relationship with the land use processes. Their sources were also demonstrated to relate most to the land-use activity. The deterioration in water quality within the study area suggested harmful effects to the human especially as it relates to domestic usages of the water. This mostly related to surpasses of some water quality parameters (e.g. Fluoride, Mercury, Pesticides such as DDT and "Malathion") of the recommended WHOand the Kenya quideline standards for drinking water quality. The study recommends an evaluation of the water quality status for different uses within the study areas and especially groundwater and surface waters. Human health aspects should also be considered. There must be j shiftt towards proper land-water-conservation practices in-corporated within the management of water resources. This must take in consideration the quality of the waters and the sources of the water pollutants.