The distribution and hydrogeological controls of fluoride in the groundwater of central Ethiopian rift and adjacent highlands |
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Authors: | Tenalem Ayenew |
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Institution: | (1) Department of Earth Sciences, Addis Ababa University, P.O.Box 1176, Addis Ababa, Ethiopia |
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Abstract: | Occurrence of fluoride (F) in groundwater has drawn worldwide attention, since it has considerable impact on human health.
In Ethiopia high concentrations of F in groundwaters used for community water supply have resulted in extensive dental and
skeletal fluorosis. As a part of a broader study, the distribution of F in groundwater has been investigated, and compared
with bedrock geology and pertinent hydrochemical variables. The result indicates extreme spatial variations. High F concentration
is often associated with active and sub-active regional thermal fields and acidic volcanics within high temperature rift floor.
Variations in F can also be related to changes in calcium concentration resulting from dissolution of calcium minerals and
mixing with waters of different chemical composition originated from variable hydrogeological environment across the rift
valley. The concentration of F dramatically declines from the rift towards the highlands with the exception of scattered points
associated with thermal springs confined in local volcanic centers. There are also interactions of F-rich alkaline lakes and
the surrounding groundwater. Meteoric waters recharging volcanic aquifers become enriched with respect to F along the groundwater
flow path from highland recharge areas to rift discharge areas. Locally wells drilled along large rift faults acting as conduits
of fresh highland waters show relatively lower F. These areas are likely to be possible sources of better quality waters within
the rift. The result of this study has important implications on site selection for water well drilling. |
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Keywords: | Ethiopian rift Flourosis Fluoride Groundwater Volcanic rocks Water quality |
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