Assessment of the quality of the Owabi reservoir and its tributaries

Abstract

Physicochemical properties, nutrient concentrations, microbial properties and concentrations of heavy metals in water and sediments from the Owabi reservoir and its tributaries, namely Atafua, Sukobri and Owabi rivers as well as the outflow of the reservoir, were determined as indicators of the extent of pollution of the reservoir. The samples were collected in December 2015, which falls within the dry season in Ghana. Nutrient concentrations in water and sediments were within permissible limits. The heavy metals (Cu, Mn, Cd, Pb and Fe) in sediments were determined using X-ray fluorescence and that in water using flame atomic absorption spectrometer. Water from the reservoir and its feeder tributaries was heavily polluted with faecal coliforms, Escherichia coli and faecal enterococci. Physicochemical properties were within the World Health Organisation’s (WHO) permissible concentrations for drinking water except for turbidity, which was significantly higher (P < 0.05). The pH of the water samples ranged from 7.68 to 7.84 in the tributaries whilst that of the dam water ranged from 8.87 to 9.01. The turbidity of the Owabi dam and its tributaries ranged from 5.98 to 42.25 NTU. The turbidity of all the water samples was significantly higher (P < 0.05) than the WHO’s threshold for potable water (5 NTU). Manganese was detected in all the water samples and ranged from 0.19 to 0.61 mg L−1. Lead concentrations in the water samples ranged from below detection limit to 0.3 mg L−1. Cd was present in only one water sample from the Sukobri River. Cu and Fe were below detection limit in all the water samples. Geo-accumulation index of Cu, Mn and Pb was less than 1 with their enrichment factors also being less than 0.5. The geo-accumulation index and enrichment factor for Cd in Sukobri River sediment were 6.41 and 11.41, respectively. Sediments from the Owabi reservoir recorded no Cd geo-accumulation indices and enrichment factors, indicating no Cd contamination in it. The reservoir was chemically unpolluted but had high levels of pathogens which pose a health risk.