Characterization of non point source pollutants and their dispersion in Lake Victoria: A case study of Gaba Landing site in Uganda

Abstract

Lake Victoria is one of the largest freshwater bodies in the world. The lake is bordered by Kenya, Tanzania, and Uganda, and has streams and rivers stretching as far as Burundi and Rwanda feeding into it. A number of studies have reported deteriorating water quality due to pollution. In this study Non Point Source Pollution was the focus and such as 68 samples and 64 samples were collected over two rain seasons and dry season, respectively. All samples were analyzed for nutrients, namely, Ammonia, Nitrite, Nitrate, and Phosphate. Portable meters were used to measure pH, EC, Total Dissolved Solids, Temperature and Dissolved Oxygen instantaneously at point of sample collection while Wagtech methods used to measure nutrients. TSS was measured using gravimetric method. Within the lake, samples were taken at for horizontal transects of 10 metres (m) interval over a distance of 50 m from the shore where surface runoff was released. At each 10 m sampling point, three samples were drawn at vertical distances of 0.5 m, 1.0 m and 1.5 m from water surface using a hand pump with graduated delivery pipe. The aim of this research is to characterize non point pollutants and their dispersion in Lake Victoria. The criterion to be maximized is the R-squared (R2) value, which is expressed in percent. The results generally show runoff during wet season increases the concentrations of Ammonia, Phosphorus, Nitrites and Nitrates and the associated dispersion is influenced by wind speed and direction, wave speed and direction. Furthermore, it was also noted that nutrient concentrations decrease as one moves deeper from the shores into the lake due to dilution.