Time and Space Dependence of Ionic Composition of the Kebena River in Addis Ababa
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2001-06
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Abstract
The Kebena River traverses Addis Ababa from north to south, The river starts upstream
from a scarcely populated area and goes to the south through the densely populated areas.
The difference in ionic compositions as one goes from upstream to down stream is then an
indication of human impact on the quality of water. The geogenic ions, which are
introduced from the natural environment through which the water passes, and the
anthropogenic ions, which mainly enter into the water by the action of man, have been
determined . The pH, conductivity, alkalinity, the chemical oxygen demand (COD),
ammonium, nitrite, nitrate, phosphate, sulfate, chloride, fluoride, sodium , potassium,
magnesium , calcium ions and silica have been determined from three different sampling
sites, which represent upstream, midstream and downstream using standard methods of
analysis.
Time and space dependence of ionic composition has been studied starting from the end of
the rain season (September, 2000) to the beginning of the small rain (April, 2001). The diy
season dominates in between. The increase in concentration of the anthropogenic ions as
nitrate, nitrite, ammonium, phosphate, COD, and chloride, as one goes from upstream to
downstream through the highly populated areas and the increase in these ions as the rain
ceased and the surface runoff decreased were very good indications of the deterioration of
water quality by human activities; by direct disposal of liquid and solid wastes to the river The Addis Ababa city solid waste disposal site is the landfill at Kore (Jimma Road). Two
samples were taken to determine the ionic composition of the runoff from this landfill.
Emphasis was given for trace elements, especially cadmium, lead, copper, and zinc,
differential pulse stripping voltammetry (DPSV) was used for their determination. The trace
elements (Cu, Pb, Cd and Zn) were not detected using DPSV, which has a detection limit of
1O'7-1O'8 M.
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Time and Space Dependence