Abstract:
Most tropical African lakes are facing problems of rapid population growth in the riparian communities, which normally
discharges pollution loads into the lakes. This has led to the deterioration of water quality in receiving lakes. Some lakes
are getting eutrophic whilst others are facing problems of siltation and heavy metal discharges, thereby reducing their
economic and aesthetic values. Some lakes are experiencing a decrease in fish production. In Rwanda, generally the
surface waters are full of sediments caused by soil erosion. The proliferation of water hyacinth and other aquatic weeds
is now a common phenomenon. The reduction in lake water levels and low fish production are also main problems of
lakes in Rwanda. In particular, Lake Muhazi has experienced a dramatic decrease in fish production since the eighties,
typified by low water transparencies and high turbidities. The lakeshores are now being developed for ecotourism and
this requires sound environmental management to make the planned activities viable.
The purpose of this study was to investigate the nutrient status of Lake Muhazi by assessing vertical and horizontal
distributions of nutrients in the Lake. The parameters studied are nitrogen, phosphorous, chlorophyll a, and Secchi disc
measurements. The nutrient levels were determined over a period of four months from July 2007 to October 2007. Four
sampling stations were located within the lake and the sampling was done fortnightly. The samples were collected at
depths of 0.5 m, 2 m, 5 m, and 1 m from the bottom of the lake. Samples were taken using a Van dorn Bottle water
sampler and were analyzed for heavy metals, TP, TN, NO2-N, NO3-N and chlorophyll-a using the Standard Methods.
Field measurements of temperature, transparency (Secchi disc), and pH were also measured. The results indicate that the
nutrient levels in the Lake are higher than previously reported figures and urgent intervention is required. It was
observed that the high nutrient levels in the lake are related to landuse activities in the catchment. It is recommended that
farming practices and erosion be controlled on the catchment to contain pollutant discharges into the Lake.
