Evaluating the Source and Fate of Nitrate in Surface and Ground Waters in Addis Ababa Area: Geochemical Approaches
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Date
2016-06
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Addis Ababa Universty
Abstract
This study was conducted to evaluate the source and fate of nitrate in surface and ground water.
The characterization of nitrate (NO3) in major rivers and aquifers of the Addis Ababa area were
investigated by Isotopic and geochemical conditions. And an overall understanding on the
sources and fate of NO3 in the surface water and the groundwater was obtained. The NO3
concentrations in both surface and ground water were very low and no samples exceed the WHO
standards while concentration of other nutrients such as PO4-, Cl- and NH4+ were higher on
surface waters.
The Redox condition estimated based on measurements of redox parameters of Eh, The analysis
revealed that most of the surface water had anaerobic condition and presence of strong reducing
conditions in the surface water and the recharge ground water. The anoxic condition is provided
by high organic matter content in the surface water and result depletion of oxygen’s.
Here the δ2H_H2O and 8δ18O_H2O result shows that the source of ground water in the city is
heavy rain fall of different regime and shallow ground water recharge hypostasis is from rain fall.
The recharge of surface water is from dam reservoirs and mixing between tap waters and ground
waters. This study brings some clear evidences that unwanted anthropogenic nutrients can be
released in both surface waters and shallow groundwater from rapidly growing cities. In addition,
these polluted waters can create a serious treat for the downstream populations, with the need to
implement expensive tertiary treatment plants to remove nitrate.
The chemical data shows that the concentrations of nutrients other than nitrate were higher and
shows the pollution of surface waters but low nitrate. From the correlation of nitrate specious
with other geochemical parameters reveals that the source for nitrate and other nutrients were
the same such as wastes from manure, septic systems, fertilizer and industries.
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Keywords
Source and Fate of nitrate