Assessment of Yatta Canal Water Quality for Irrigation, Machakos County, Kenya
Mang'oka, Joseph Muli
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The erratic global precipitation pattern over the years due to climate change coupled by rising human population has increased dependence on irrigated agriculture to meet food demand. Irrigated agriculture is essential to produce acceptable quality and yield of crops but if left unmonitored, can lead to salinization and eutrophication of water sources. In Kenya, the problem of water quality degradation cannot be underestimated and numerous factors have contributed to the degradation of important irrigation water resources due to changes and intensity in land use activities. This study was carried out from July to December 2014 to evaluate the Yatta canal water quality for irrigation in Machakos County, Kenya. Specific objectives included assessing the physicochemical and biological properties of the canal water, assessing the variation in physicochemical and biological concentrations of canal water along the sampling stations and comparing the canal water quality with national and international standards. Water samples from twenty stations were collected during dry and wet seasons and analyzed for major cations, anions and fecal contamination. The average values of canal water temperature, pH, total dissolved solids, turbidity, dissolved oxygen and electrical conductivity during dry and wet seasons respectively are; 25.4°( and 22.6°(; 7.4 and 7.2; 318.3mg/l and 438.7mg/l; 47.7NTU and IOO.2NTU; 6mg/l and 6.6mg/l; 0.13dS/m and 0.16dS/m. These parameters are within recommended NEMA and FAO limits for irrigation water except turbidity. Mean concentrations of canal chemical parameters during dry and wet seasons respectively are; 4.8mg/l and 13.1mg/l nitrates, 7.2mg/l and 10.7mg/l sulphates, O.02mg/l phosphates, 2mg/l and 14.3mg/l chlorides, 79.9mg/l and 46.9mg/l bicarbonates, 2.9mg/l and 3.8mg/l potassium ions, 8.1mg/l and 5.9mg/1 calcium ions, 2.9mgll and 2.2mg/l magnesium, 17.7mg/l and 14.7mg/l sodium, O.6mg/1and O.5mg/l iron, 1.35me/l and 1.3me/l for Sodium Adsorption ratio. These parameters are within permissible standards with the exception of nitrates. Average levels of fecal E. coli are 2cfull OOmlin both dry and wet seasons while fecal coliforms are 91cfullOOml in dry and 116cfU/IOOml in wet season. Paired Hest was used to analyze the seasonal variation in concentrations ofthe canal parameters while onesample Hest was used to determine variations in canal physicochemical and biological properties with national and international standards. One-way ANOVA test was used to determine variations of canal parameters along the sampling stations. Concentrations of all the physicochemical and biological parameters with the exception of Sodium Adsorption Ratio and fecal E.coli shows significant (p<O.05) seasonal variation and compared with national and international irrigation standards. There are significant variations (p<0.05) along the sampling stations of the canal. Based on the results, contamination of the canal water is due to animal and human direct access, surface runoff and leaching of nutrients into the canal water during the rainy season. The levels of nitrates and bacterial contamination are above the permissible guidelines by FAO and Kenya's National Environmental Authority hence canal water is unsuitable for irrigation purposes especially when used in the cultivation of horticultural crops and salads.