Abstract:
Tropical reservoirs are important for numerous socioeconomic and ecological reasons,
including water supply, fishing and flood control. These functions are easily
compromised, however, when reservoirs undergo accelerated sedimentation with
increased inputs of chemical contaminants. The present study applied the concept
of sediment core analysis to evaluate the sedimentation rate in Owabi Reservoir,
which has served as a source of drinking water supply in Kumasi, Ghana, for nearly
a century. The temporal variation of contamination from heavy metals was also assessed
over this period. The sedimentation rate for Owabi Reservoir was estimated
to be 6.82 mm/year, suggesting a relatively low rate of sedimentation, which is ecologically
healthy in preventing a rapid loss of reservoir water volume. Heavy metal
concentrations in the sediment cores taken from the reservoir reflected varying
degree of contamination from the 1930s to 2010s. The concentration of iron (Fe)
(1,560–1,770 mg/kg) was found to be the highest among the metals in the sediment
core, while mercury (Hg) concentration (0.01–0.04 mg/kg) was the lowest. Lead (Pb)
contamination peaked in the 1980s. Arsenic (As) and mercury (Hg) contamination
exhibited more recent peaks in the 2000s, coinciding with recent widespread issues
of artisanal and small‐scale gold mining (ASGM) in Ghana. Thus, even though ASGM
activities are known to occur in remote districts, releases from such activities might
eventually contaminate reservoirs designated as urban drinking water supplies.
