Water Quality of the Weija Reservoir after 28 Years of Impoundment

The water quality of the Weija Reservoir was assessed and the various sources of contaminants were identified in order to provide scientific basis for finding appropriate remedies to the contamination problems that may confront the Reservoir. Monthly water samples were taken from three sampling stations in the Weija Reservoir and analysed for physico-chemical parameters in the laboratory. The mean pH values of the sampling sites were within the recommended range of 6.5–8.5 for potability and sustenance of aquatic life. The ionic dominance pattern observed was Na > Ca > Mg > K and HCO3 > Cl > SO4, indicating partial cationic characteristics of sea water and anionic characteristics intermediate between fresh water and sea water. Dissolved oxygen (DO) levels were 102.5%, 81.5% and 82.7% saturation for Weija Intake, Machigani and Galilea, respectively. Thus, the oxygen conditions in the Weija Reservoir were sufficient to support fish and other aquatic life. Maximum BOD level was 8.1 mg/l at Weija Intake. Compared with previous studies on the Weija Reservoir, results of the study show a slight increase in nitrate, ammonia, sulphate and phosphate levels. Generally, the levels of nitrate, sulphate, phosphate, trace elements (e.g. manganese and iron) and BOD were moderately high. Anthropogenic activities, such as stone quarrying, dumping of domestic wastes, as well as run-offs from agricultural activities and the occurrence of algae, are some of the sources of contamination identified in the study. Tougher legislation, stricter enforcement of existing regulations, matching of non-technical and technosocial remedial measures and education are among the recommendations made for the protection of the Weija Reservoir. Introduction Reservoirs, which are man-made lakes, are vital aquatic ecosystems that serve important environmental and economic purposes, including potable water supply, hydroelectric power generation, irrigation agriculture and fisheries. During the last 4–5 decades, many reservoirs such as Volta, Vea, Barekese, Kpong and Weija have been created in Ghana by damming some rivers. Water supply reservoirs (including Weija Reservoir) in several parts of Ghana ensure adequate and sustainable source of raw water throughout the year for treatment to provide potable water to major cities and towns. The fresh water obtained directly from these reservoirs to satisfy the needs of rapidly growing urban populations are, however, variable in quality due to pollution (DFID, 1999). The main sources of water pollution include indiscriminate disposal of domestic, industrial and municipal solid and liquid wastes; improper land use; poor agricultural practices and environmental degradation. Previous studies on the limnology of some reservoirs for water production in Ghana include Weija Reservoir (Ansa-Asare, 2001; Ameka et al., 2000; Ansa-Asare & Asante, 1998; Larmie, 1988; Biney, 1987, 1982; Kpekata & Biney, 1979; Amuzu, 1975); Barekese Reservoir (Amuzu, 1973); Kpong Headpond (Antwi & Ofori-Danson, 1993; Biney, 1985). Other available data on the water quality of some inland water systems in Ghana include Ansa-Asare & Asante (2000), Ampofo (1997), Ansa-Asare (1995, 1992), Biney (1985), Odei (1975) and Ayibotele (1974). Ansa-Asare & Asante (1998) compared the nutrient status of the Weija and Kpong reservoirs in Ghana by determining the seasonal indices and interannual changes over a 5-year period from 1993-1997. The nutrient levels and seasonal distribution of nutrients were found to be higher in the Weija Reservoir than the Kpong. Seasonal variation also showed higher levels of nitrates in the rainy season at Weija than at Kpong. The monthly trend of nitrates showed a unique pattern in the months of March and May, the main ploughing periods for farming in the Weija catchment area when most fertilizer is applied. In general, over the 5-year period, there were no trends in nutrient levels. However, sulphates showed a gradual decrease in spatial distribution from 1993-1997, and phosphate index in January at both Weija and Kpong was high. Bosque-Hamilton et al. (2004) compared Weija, Brimsu and Inchaban reservoirs in Ghana and found that the Weija Reservoir was well mixed and aerated but less transparent with high phytoplankton