Heavy Metals Inflow into Lake Muhazi, Rwanda

Abstract

Most tropical African lakes are facing pollution problems due to the rapid population growth and industrialization in their riparian communities. Lake Muhazi in Rwanda is one of such lakes which has experienced a dramatic decrease in fish production since the eighties, with also reports of 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 assess heavy metal pollution in the tributary rivers of Lake Muhazi. The concentration of heavy metals in major tributaries was monitored for the period July to October 2007. The parameters studied are cadmium, chromium, copper, iron, lead, manganese, zinc, pH and temperature. Fourteen sampling stations on the Inflow Rivers and the spillway were monitored fortnightly. The samples collected for heavy metal analysis were preserved and stored in cooler boxes and analyzed in the laboratory using Standard Methods. Temperature and pH were measured in the field using HACH field testing kits. The concentration (mean ± standard deviation) of Zn was found to be 0.040±0.103 mg/L, Cd 0.031±0.007 mg/L, Pb 0.487±0.452 mg/L, Fe 7.53±13.34 mg/L, Mn 1.01±1.31 mg/L, chromium 0 mg/L and copper 0 mg/L. The concentrations of measured parameters deviate much from the recommended ones thus posing serious problems to aquatic life. It has also been shown that the high metal concentration levels in Lake Muhazi are related to landuse activities in the catchment. It is thus recommended that farming practices and erosion be controlled in the catchment to contain pollutant discharges into the lake. Lead is the main anthropogenic pollutant which has been found in the watershed of Lake Muhazi.

Spatio-seasonal variation of water quality influenced by land use and land cover in Lake Muhazi

“…In particular, most tropical lakes in Africa face pollution problems due to rapidly growing populations associated with greater demand for agricultural land, rising economies, and industrialization 20 , 21 . These latter have resulted in increased water consumption and wastewater discharge, which causes heavy pollution 22 .…”

USLE-Based Assessment of Soil Erosion by Water in the Nyabarongo River Catchment, Rwanda

“…This pollution is accelerated by intensive agriculture due to rapid population growth and industrialization in their riparian communities [12]. As a consequence, nutrients from erosion have caused the infestation of water hyacinth in Lake Victoria and the Akagera river basin [13,14].…”

“…Lake Victoria, which drains the water from the Nyabarongo River through the Akagera River has been listed among the top 10 most highly polluted water bodies in the world [ 11 ]. This pollution is accelerated by intensive agriculture due to rapid population growth and industrialization in their riparian communities [ 12 ]. As a consequence, nutrients from erosion have caused the infestation of water hyacinth in Lake Victoria and the Akagera river basin [ 13 , 14 ].…”

Seasonal assessment of drinking water sources in Rwanda using GIS, contamination degree (Cd), and metal index (MI)

“…There are also poor sewage systems and common use of public latrines and septic tanks in both rural and urban areas (Aboniyo et al 2017). Although several scholars (Doyle and Shanahan 2010; Karamage et al 2016; Nsengimana et al 2012; Nhapi et al 2011) have conducted water quality assessments, they lacked the seasonal measurements necessary for understanding temporal changes in water quality, so that appropriate seasonal drinking water source management mechanisms can be applied. Regular water quality assessment would help water resource managers, environmental health officers, and the whole community to better understand and correlate seasonal variability and drinking water quality.…”