Heavy metal pollution and nutrient levels in Lake Muhazi, Rwanda

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

Heavy metal pollution and nutrient levels in Lake Muhazi, Rwanda

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

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