Phosphorus Modeling, in Lake Tana Basin, Ethiopia

Abstract

N and P found naturally in soils, however agricultural activities increased the concentration of these nutrients resulting in poor water quality and eutrophication. Excessive concentration of P is the most common cause of eutrophication in fresh water lakes and reservoirs while N is the key controlling nutrient in ocean. According to recent researches, a comparison between N and P resulted in a general rule that reduction of N loading cannot decrease eutrophication as that of P. To be able to assess the potential of nonpoint source P pollution and to develop proper management strategies to reduce P losses to surface waters, it is essential to understand the major processes involved in P transport. Terrestrial processes are responsible for P inputs from upland and riparian areas while aquatic processes include stream bank inputs and in stream P inputs, outputs and transformations. This study focuses in modeling dissolved P load from Lake Tana Basin. Semi-distributed model is used considering the contribution of base flow; interflow and overland flow to dissolved P. Amazingly, the model predicted phosphorus load with an excellent efficiency with limited data we have and many constraints. Parameter analysis indicated that the contribution of overland flow to dissolved P is higher in most of Lake Tana Basin catchments hence agricultural could be the major source of P in the stream. The fertilized areas would also have great contribution to surface runoff P concentration. Some management practices are proposed from literatures to reduce P load.