NON POINT POLLUTION LOADING IN A SELECTED MICRO- CATCHMENT OF THE LAKE VICTORIA BASIN

摘要

Although the UN Millenium Declaration draws attention to the importance of water in supporting development and eradicating poverty, the quality of water in Lake Victoria, the second largest fresh water in the World, is degrading as a result of poor management of agricultural land-use. The objective of this study was to determine exports of sediments, nitrogen and phosphorus in Kibaale micro-catchment. Kibaale river was sampled upstream and downstream intensively at two days interval during the growing seasons for four years. For other remaining periods of the year the river was sampled every two months. The transfer of sediments and nutrients was determined by the use of the AnnAGNPS model. Results show sediments and phosphorus export rates were relatively high on degraded rangelands mixed with annuals, and on woodlands for nitrogen. Perennial mixed with annual crops were second for sediments, and third for phosphorus and nitrogen. Grasslands were ranked fourth in export of sediments, phosphorus and nitrogen. Runoff was generated equally from degraded range mixed with annual crops, perennial mixed with annuals, woodlands and grasslands. But most of the sediments and TP were coming from degraded ranges mixed with annual crops (66.94% of sediments and 65.52% of TP), followed by perennials mixed with annual crops (26.71% of sediments and 25.25% of TP). About 70% of N into Kibaale was equally coming from degraded range, annual and perennial crops. Similarly, grasslands and woodlands yielded equal quantities of TN into the River Kibaale (about 15%). The Forest contributed very little for all parameters. The hot spot areas for sediments, and both nutrients were well-drained, deep and permeable soils in the depressions below hill slopes and very compacted grazing areas in the lower part of the micro-catchment.