Assessment of physical and biochemical parameters of pollution in freshwater reservoirs in Kericho tea estates, Kenya
Akungah, Daniel Nyagetiria
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The physical, biological and biochemical characteristics in four small private man-made reservoirs in the central part of Kericho district, Kenya were studied between November 2001 and March 2002. The main aim of the study was to relate the land management in tea estates and water quality. This is important because the Kericho area forms a catchment for many rivers flowing to Lake Victoria. Over the study period, forty depth integrated water samples were collected from each of the four dams. A total of 25 parameters were investigated over the study period to provide the baseline data for future reference in these water bodies. In the field, temperature, pH, electrical conductivity, and dissolve oxygen were determined at every site using a multiple electrochemistry analyzer meter while transparency was determined using a Secchi disc. During sampling, 3-litre water samples were collected for chlorophyll-a analyses while 250ml water samples were collected for both chemical and bacteriological quality assessment. In the laboratory, the water samples were analyzed for heavy metals; cadmium, lead, copper, silver, iron, manganese, magnesium and zinc by spectroscopic methods. Water samples for total nitrogen and nitrates were digested by steam distillation method and measured calorimetrically, while the photometric method was used for orthophosphorus and total phosphorus determination. The presence of total coliforms and faecal coliforms were determined by the multiple tube fermentation techniques while plate count method was employed in the determination of total viable counts. Chlorophyll-a was extracted by methanol and measured spectrophotometrically. Total suspended solids were estimated by filtering 500ml sample using pre-weighed oven dried 0.45mm Millipore filter papers. For 250ml water, samples in biochemical oxygen demand (BOD5) were incubated for five days and the remaining dissolved oxygen measured by the multiple electrochemistry analyzer meter above. The overall mean measurements for temperature was 18.11°C, Secchi depth 27.84cm, pH 6.72 units, electrical conductivity 39.95mS, percent dissolved oxygen 73.14%, BOD 28.55mg/l and suspended solid 126.97mg/l. It was observed that Kerenga dam recorded the highest mean levels in iron (6.379mg/l), magnesium (1.479mg/l), zinc (2.472mg/l), copper (0.065mg/l), nitrates (5.47mg/l), orthophosphates (0.017mg/l), total nitrogen (14.84), total phosphorus (0.098), chlorophyll-a levels (0.055mg/l) and BOD (31.15mg/l) while Jamji record highest mean levels in silver (0.191mg/l) and suspended solids (174mg/l). Sambret dam, which was our control reservoir, recorded the lowest levels of nutrients, chlorophyll-a and highest levels of manganese (1.172mg/l). Total coliform bacteria were more prevalent in Kerenga and Jamji; faecal coliforms 99MPN/100ml, total coliform (349MPN/100ml) and total viable counts (4.6x105 cfu/ml) followed by Sambret and Chagaik in that order. The results show that the levels of metals (except manganese and iron) and nitrates are below the maximum permissible levels set by WHO in drinking water. However, as regards microbial analyses, the dams were observed to be highly polluted by faecal and total coliforms and therefore not safe for domestic purposes before treatment. In addition, three of the four dams were found to be highly eutrophic regardless of the criteria used for their classification. Agricultural run-offs, domestic effluents, geo-chemical sources, municipal and urban run-off as well as leaching of nutrients were some of the possible contamination sources to the reservoirs. It was therefore proposed that nutrient containment, especially phosphorus, be given special attention. For Kerenga dam, this might require corporate action between the Brooke Bond tea company and the Municipal council to develop stabilization ponds. There is need therefore for an extended study to model the water quality of these dams and to be able to recommend the appropriate treatment process that suits these water bodies.