An assessment of water quality of Angaw River in Southeastern Coastal Plains of Ghana

Abstract

Physico-chemical and bacteriological water quality of the Angaw river were investigated at three different locations on the river. A range of water quality variables were measured in the river over a period of 12 months. The river was characterized by high ionic content. Relatively higher levels of ionic constituents occurred at the upstream while lower concentrations were observed downstream due to the influence of River Volta, which has lower ionic content. There was a dominance of Na and Cl over the cationic and anionic components, respectively, due to the effect of atmospheric deposition of sea salt. Calcium and magnesium showed a strong linear correlation r = 0.993 significant at p < 0.05, indicating biogeochemical mineral weathering. The water was moderately hard (mean range of 89-133 mgl -1 CaCO 3), salty and neutral with mean pH of 7.3±0.13. Conductivity, TDS and the major ions varied seasonally with elevated levels in the rainy season. However, nutrients levels were low during the study period and did not give any clear seasonal variation. The bacteriological quality of the water was poor, rendering it unsafe for domestic purposes without treatment. However, the water was suitable for primary and secondary contacts such as swimming and fishing. The poor bacteriological quality was due to direct contamination by animal and human wastes. Introduction Rivers are the most important freshwater resource for man. Social, economic and political development has been largely related to the availability and distribution of freshwaters contained in riverine systems. Water quality problems have intensified through the ages in response to the increased growth and concentration of populations and industrial centres. Polluted water is an important vehicle for the spread of diseases. In developing countries 1.8 million people, mostly children, die every year as a result of water-related diseases (WHO, 2004). Ghana's water resources have been under increasing threat of pollution in recent years due to rapid demographic changes, which have coincided with the establishment of human settlements lacking appropriate sanitary infrastructure. This applies especially to peri-urban areas, which surround the larger metropolitan towns in the country. Many such settlements have developed with no proper water supply and sanitation services. People living in these areas, as well as downstream users, often utilise the contaminated surface water for drinking, recreation and irrigation, which creates a situation that poses a serious health risk to the people (Verma & Srivastava, 1990). The River Angaw runs through farmlands and rural communities before its confluence with River Volta. Not much studies have, however, been done on the water quality of the river. This would be of importance since water supply treatment was being planned to supply water to the entire community at the time of the study. A number of factors influence water chemistry. Gibbs (1970) proposed that rock weathering, atmospheric precipitation, evaporation and crystallisation control the chemistry of surface water. The influence of geology on chemical water quality is widely recognised (Gibbs, 1970; Langmuir, 1997; Lester & Birkett, 1999). The influence of soils on water quality is very complex and can be ascribed to the processes controlling the exchange of chemicals between the soil and water (Hesterberg, 1998). Apart from natural factors influencing water quality, human activities such as domestic and agricultural practices impact negatively on river water quality. It is,