சுற்றுச்சூழல் பகுப்பாய்வு வேதியியல் இதழ்

Variations in the Physico-Chemical Characteristics of Water in Five Peri- Urban Reservoirs in Kiambu and Nairobi City Counties, Kenya

Abstract

Kitur Esther, Kiplagat Kotut and Kerich Richard

Information on reservoirs is important as it forms a vital baseline for among others the detection of undesirable changes in water quality. Variations in the physicochemical characteristics of water were investigated in five peri-urban reservoirs Uhuru reservoir located in Nairobi City County and Ruiru, Ngewa, Comte and Kianjjibbe in Kiambu County between February 2014 and January 2015. The aim of the study was to establish the quality of water. Mean Secchi depth recorded in cm was 0.7 ± 0.9 in Uhuru, 0.9 ± 0.43 in Ruiru, 0.1 ± 0.04 in Ngewa, 0.1 ± 0.6 in Comte and 0.3 ± 1.3 in Kianjjibbe. Mean temperatures in °C were 23.8 ± 1.8 in Uhuru, 21.6 ± 2.2 in Ruiru, 24.3 ± 2.9 in Ngewa, 23.4 ± 1.6 in Comte and 24.0 ± 1.9 in Kianjjibbe. Electrical conductivity in μS cm^-1 was 90.4 ± 23.81 in Uhuru, 45.8 ± 5.7 in Ruiru, 195.5 ± 37.3 in Ngewa, 113.3 ± 20.5 in Comte and 298.94 ± 41.5 in Kianjjibbe. pH was 7.4 in Uhuru and Ruiru and 7.2, 7.3 and 7.7 in Ngewa, Comte and Kianjjibbe respectively. Dissolved oxygen in mgL^-1 was 7.1 ± 0.7 in Uhuru, 7.1 ± 0.26 in Ruiru, 6.2 ± 1.1 in Ngewa, 7.6 ± 1.1 in Comte and 9.0 ± 0.8 in Kianjjibbe. Total alkalinity in mgL^-1 CaCO₃ was 35.5 ± 8.8 in Uhuru, 18.0 ± 0.24 in Ruiru, 83.9 ± 7.9 in Ngewa, 41.1 ± 8.9 in Comte and 110.2 ± 15.9 in Kianjjibbe. Nitrate nitrogen μg L^-1 was 9.8 ± 1.37 μg L^-1 in Uhuru, 9.0 ± 12.5 in Ruiru 4.2 ± 0.43 in Ngewa, 7.1 ± 5.56 in Comte and 13.6 ± 1.14 in Kianjjibbe. Total nitrogen in μg L^-1 was 33.1 ± 22.7 in Uhuru, 39.8 ± 3.0 in Ruiru, 34.1 ± 22.5 in Ngewa, 40.5 ± 36.9 and 32.5 ± 28.7 in Comte and Kianjjibbe reservoir respectively. Total phosphorus in μg L^-1 in the reservoirs was 0.8 ± 0.14 in Uhuru, 1.0 ± 0.02 in Ruiru, 1.0 ± 0.77 in Ngewa, 1.0 ± 0.82 in Comte and 2.7 ± 0.25 in Kianjjibbe. Soluble reactive silica in mgL^-1 was 3.4 ± 0.47 in Uhuru, 4.0 ± 0.64 in Ruiru, 7.3 ± 0.7 in Ngewa, 5.9 ± 0.15 in Comte and 7.0 ± 199 in Kianjjibe. Peak values of total nitrogen and total phosphorus were recorded during the wet season while high soluble reactive silica was recorded during the dry season. There was a significant difference in all measured physcio-chemical parameters between the reservoirs (p<0.001, df=59). The study concludes that the reservoirs investigated varied in levels of physico-chemical properties. The variation was attributed to differences in rainfall, volume of outflow and use dynamics of the water of the reservoir.