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QUALITY ASSESSMENT OF STREAM WATER AND BED SEDIMENTS: A CASE STUDY OF URBANIZATION IMPACTS IN A DEVELOPING COUNTRY

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

Citation:  Paper number  701P0904,  . (doi: 10.13031/2013.17380)
Authors:   M. N. Tijani and S. Onodera
Keywords:   Stream water, stream sediment, quality assessment, heavy/trace metals, contamination, urbanization impact, Ibadan, Nigeria.

Hydrogeochemical analyses and evaluation of surface water and stream-bed sediment samples from 40 different locations along the stretches of stream networks within Ibadan metropolis, SW Nigeria were undertaken with respect to the influence of urbanization and anthropogenic activities on the quality status of urban drainage system in a developing country. Results show that the surface water samples have generally low TDS with average value of 517mg/l, while average concentrations of the dominant ions are 75mg/l (Na) and 30mg/l (Ca) representing 51% and 18% respectively of the total cations and Cl (av. 86mg/l) and HCO3 (av. 71mg/l) representing 40% and 21% respectively of the total anions. However, indication of urbanization impacts on the surface water quality is revealed by the NO3 concentrations with values of 22.8 366mg/l, exceeding the WHO limit of 50mg/l in 85% of the sampled locations. The high NO3 as well as the variability of sodium and chloride concentrations are clear indications of contamination through a number of point-source inputs of domestic sewage, municipal effluents and waste dumps along the stretches of the drainage system in the study area.

The impact of such anthropogenic activities is also revealed by the trace metal enrichment of the stream bottom sediments with enrichment factor (EF) of about 60 (Hg), 3.5 (As), 1.5 (Pb), 0.6 (Cu) and 0.5 (Zn) which imply that anthropogenic sources account for about 90-95% (Hg), 10-80% (As), 10-70% (Pb), 10-55% (Cu) and 10-40% (Zn) of the respective total concentration. Also an assessment of the metal bioavailability revealed that 19.6% (Cu), 10.7% (Pb) and 29.4% (Zn) of the respective metal concentrations are in adsorbed form, the possible remobilization and trophic transfer of which calls for environmental concerns. This study highlighted the need to understand the interactions between the populated urban catchments and the drainage systems and in essence the environmental pollution management of urban drainage systems in developing countries.

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