Non-point Source Pollution into Lake Victoria from Bukora, Uganda Sub-catchment

Abstract

Non-point source pollution from agricultural land is a major contributor of N, P and sediments resulting into eutrophication and siltation of water bodies. The extent of this pollution is accelerated by poor land management practices that lead to extensive soil erosion. PoUutant concentrations and loads from two micro-catchments of Bukora sub-catchment. a predominantly agro-pastoral area of Rakai district. were studied over a three-year period. The two microcatchments are drained by two rivers. which eventually discharge into Lake Victoria. Three hydrological stations were constructed onto the two rivers and water sampling and river discharge measurement routine is carried out. During the study period, highest rain fall amounts were recorded in April, while peak river discharge (Oow rate) occurred during July, signifying a 3-months ground recharge period. Concentrations and loads of Total N (TN) and Total P (TP) were related to Total Suspended Solids (TSS) indicating the contribution of N and P-rich sediments toN and P loading. Seasonal trends in TSS, TP and TN concentrations and loads were closely related to river discharge. Mean annual concentrations for TN ranged from 3.2 to 10.4 mg L^-1 with loads of 40 to 70 ton yr^-1. Annual means for TP ranged from 0.2 to 0.4 rng L^-1 wilh loads of 4 to 51 ton y^-1, while TSS ranged from 12 to 94 mg L^-1 with loads of 2 to 40 ton yr^-1. Concentrations and loads ofTSS, TN and TP were reduced across a wetland, especially during periods of low flow. High sediment, N and P pollutant concentrations and loads are likely a result of extensive soil erosion in the area_ Results call for promotion or better land management practices so as to reduce non-point pollution of rivers and consequently. lake Victoria.

Keywords: Eutrophication, Water quality. Watershed management. Wetlands .