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Seasonality Impact On Pollution Loads Of Downstream Quality Of Municipal Drainage River, Uyo, Nigeria

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  21st Century Watershed Technology: Improving Water Quality and Environment Conference Proceedings, 21-24 February 2010, Universidad EARTH, Costa Rica  701P0210cd.(doi:10.13031/2013.29416)
Authors:   Obot E Essien
Keywords:   keywords: Seasonality effect, municipal drainage river, pollution load, Ikpa basin,Nigeria

Seasonality in climate and streamflow exist over Uyo municipality in Ikpa river basin, a humid tropical rainforest area of Nigeria; mean annual rainfall was 3164mm, streamflow monthly distribution varied from 18% of annual runoff in the wet season to only 3% in the dry season. Significant impact was observed in mean deviations of concentrations of composition (or pollutants) in the wet and dry season in the river draining Uyo municipality. Heavy metals concentrations reduced drastically in the dry season more than in the rainy season when NPS was high, and suggesting that drainage of municipal waste water/storm water with loads of industrial waste was responsible for high metal pollution concentration in the drainage river in the wet season. Generally, the concentrations of nutrients increased during dry season, especially potassium, calcium, magnesium, phosphate and sulphates; however, nitrates and sodium concentrations were lower in the dry season than in the wet season. Alkalinity was maximum at the downstream of the upper subreach during the rains and minimum at the downstream of the lower subreach during the dry period. Coliform counts recorded the highest pollution concentration (1300 mgl-1) in the dry season at the downstream of the lower subreach while the least count (800 mgl-1) was recorded (in the rainy season) at the upstream station of the upper subreach, reflecting the pollution effect of msw leachate effluent and sewered waste water at proximity to it. Highest BOD had (1630 mgl-1) was in the wet season close to abattoir while minimum concentration (350 mgl-1) occurred at the upstream of the upper subreach. Total suspended load had its least value upstream of the upper subreach and highest value at downstream of the lower subreach in the dry season. Salinity increased in the dry season with the effect of evapo transpiration and reduced downstream of the lower subreach in the wet season.

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