Exponential Model of Surface Runoff Pollutant Dispersion in Lake Victoria, Gaba, Uganda

Abstract

Commonly used pollutant dispersion models in aquatic systems assume uniform mixing. This study aimed at one dimensional exponential modeling approach which does not involve assumptions of unmeasured parameters. Assessment of different land-use activities and quantification of pollutant loads and dispersion into the Lake was done. One-way ANOVA was used for testing difference in nutrients concentration at the sampling points and models were developed based on mathematical method of series and sequence. Land-use in Gaba area were built up areas (36.1%), wetlands (30.6%), Lake Victoria water (20.5%) and subsistence farmland (8.30%). Gaba fish landing site was identified as non point source (NPS) pollution hotspot and runoff from this site conveyed nutrients that contributed significantly to pollution of the Lake. Seasonal comparison of the Lake water revealed ammonia-N, nitrite-N and ortho-phosphate with higher concentration during the rainy season while nitrate-N exhibited higher concentration during dry season due to nitrification process. The respective distances traversed by nutrients were found to be 36 m for ammonia-N, 40 m for nitrite-N, 38 m for nitrate-N and 42 m for ortho-phosphate. The respective model concentrations of the pollutants compared well with measured concentration at the traversed distances even after rainfall events. However, results indicated effect of assumption of uniform mixing on nitrite and nitrate concentration. With elevated nutrients level, fish species would most likely become unavailable in near shore waters because they are unable to exploit the environment properly. The findings provides an alternative explanation to the ever dwindling fish stock within the lake and reduced fish catch by fishermen in Lake Victoria especially along shore settlement.