Distribution of Heavy Metals in Lake Muhazi, Rwanda

The pollution of lakes is mainly conceived in terms of nutrient levels and eutrophication with the consequent development of algal blooms and fish kills. However, heavy metals are increasingly becoming prominent especially for water bodies closer to urban and mining areas. This study focuses on heavy metal pollution in lakes using a case study of Lake Muhazi in Rwanda. The study characterized the horizontal and vertical distribution of heavy metals in the Lake, with the research conducted from July to October 2007. The parameters studied are cadmium, chromium, copper, iron, lead, manganese, zinc, pH and temperature. The samples were collected at different depths in the Lake using a Van Dorn Bottle water sampler, and were analyzed using standard methods. The temperature and pH were measured in the field us- ing HACH field testing kits. The findings indicated that the mean concentration of Zn was 0.041±0.045 mg/L, Cd 0.026±0.029 mg/L, Pb 0.292±0.442 mg/L, Fe 0.756±0.734 mg/L, and Mn 0.340±0.336 mg/L. Chromium and copper were not detected in the water samples. The findings indicate that the concentrations of Cadmium, Iron and Lead far exceeded the recommended levels for aquatic life at all sampling points. The high levels of heavy metals are attributed to the ripar- ian landuse practices such as uncontrolled agriculture, urban runoff and mining activities around the Lake. It is recom- mended that a detailed study of the catchment be carried out to identify and isolate the main sources of heavy metals in the Lake so that appropriate control measures could be developed.