Heavy metals inflow into Lake Muhazi, Rwanda.
Most tropical African lakes are facing pollution problems due to the rapid population growth and industrializa- tion 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.
Heavy metal discharge into Lake Victoria
Water samples from different sampling sites located in the Ugandan cities of Kampala, Jinja and Entebbe as well as the remote Ssese Islands, were analyzed for concentrations of Cd, Cr, Cu, Ni, Pb and Zn. Both Kampala and Jinja have large industrial areas while Entebbe has Uganda's largest airport. Household and industrial wastes are discharged into Lake Victoria largely untreated. The objectives of this study were to: 1) evaluate concentrations of the metals in discharge from the selected sites; 2) determine whether or not wetlands impacted on the magnitude of metal discharge into the lake, 3) determine and assess heavy metal levels in drinking and irrigation water; 4) evaluate heavy metal related risks for humans and the environment. 
 
The discharges from the cities contained rather high concentrations of Cd, Cu, Pb and Zn in comparison with Swedish environmental guidelines. In Kampala and Jinja, samples were taken before and after water had passed through areas of wetland. The results show a reduction of these metals as the water passed through these areas. The reduction was especially noticeable in Kampala, where metal concentrations were reduced by up to 99%. The concentrations of all metals but Ni were alarming in Lugogo and Mpanga along Nakivubo channel (running through central and industrial areas in Kampala), these sites also being used for household farming. Some of the results from Jinja could be explained by the former Cu mine at Kilembe. The activity at the airport of Entebbe seemed to cause heavy metal pollution in nearby waters. Areas of special concern regarding the environment were all sites along Nakivubo channel, especially since the concentrations of Cd, Pb and Zn were high already at its emergence point in Makerere. In Jinja and Entebbe, all sites had Cd- and Zn concentrations exceeding the given guideline for sub-lethal or chronic effects. 
 
The expected result of lower concentrations in water outside Kalangala of Ssese Islands than outside Kampala, Jinja and Entebbe was not confirmed. The finding that the Ssese Islands had higher concentrations of Pb and Cr than 55% of the sampling sites in the cities was most surprising. Only 45% of the city sites had lower Cu concentrations than the Ssese Islands. The high concentration of Pb at Ssese Islands is alarming. The concentration was above the Swedish environmental guideline used, and there were no point sources of this metal on the island. Possible sources are therefore transport via air and/or water from the riparian countries as well as unauthorized dumping of wastes. 
 
The results from all sampling sites were compared with WHO's guidelines for drinking water. Only the Kampala sites Makerere, Lugogo and Mpanga exceeded the guidelines for Pb. Similarly, Cd and Ni concentrations at Makerere and Lugogo exceeded the guidelines. 
 
Concentrations of Pb and Cd were high at the majority of the sites. This is alarming since these metals are among the most hazardous to humans and the environment. Reduced discharge of the other metals is also important since low concentrations can accumulate and have negative longterm effects. The importance of wetlands as a purifying media must be recognized and protected. Efforts should also be put into limiting the sources of metals since treatment always means that it will end up somewhere else. Conversion to unleaded petrol as well as proper maintenance of dumping sites could lead to reduced metal leakage and decreased unlawful dumping in the lake. Implementation and enforcement of environmental legislation are most important.
The Dynamics of Human-Environment Interactions in the Tropical Montane Agrosystems of Rwanda: Implications for Economic Development and Environmental Stability
Using a historical-ecological approach, this paper explores those human and environmental processes that have shaped the montane agrosystems of Rwanda. The focus is on how the subsistence systems (pastoralism and cultivation) have interacted with a diversity of demographic, socio-economic, and political variables through time to create a high-density "island" within the interlacustrine region of Central Africa. Of particular concern are landscape and settlement changes induced by agricultural and economic development policy, natural resource management, and demographic growth. A key question considered is whether Rwanda is moving toward agricultural "involution" or "intensification" in its response to accelerated population growth. Conclusions regarding future population-resource relationships are considered. RESUME La dynamique des interactions entre la population et 'environnement dans les agrosystemes montagnards tropicaux du Rwanda: Implications pour le developpement economique et la stabilite de I'environnement. Cette etude utilise une approche historico-ecologique pour explorer les processus humains et naturels qui ont modele les agrosystemes montagnards du Rwanda. Elle se concentre sur la maniere dont les systemes d'autoconsommation (pastoralisme et culture) ont interagi au cours du temps avec diverses variables demographiques, socioeconomiques et politiques, pour creer une "ile" densement peuplee au sein de la region inter-lacustre de 1'Afrique centrale. L'etude porte un interet particulier aux changements de paysage et de peuplement causes par la politique de developpement agricole et economique, la gestion des ressources naturelles et la croissance demographique. Un question primordiale se pose: le Rwanda se dirige-t-il vers une "involution" ou "intensification" agricole en reponse a une croissance demographique acceleree? Des conclusions concernant les relations futures entre la population et les ressources sont avancees. ZUSAMMENFASSUNG Die Dynamik der Wechselwirkung MenschUmwelt im tropischen, bergigen Agrarsystem von Rwanda: Folgerungenfir wirtschaftliche Entwicklung und Umweltstabilitiit. Unter Beriicksichtigung von historischen und okologischen Aspekten untersucht diese Veroffentlichung die menschlich und umweltbezogenen Prozesse, die die bergigen Agrarsysteme in Rwanda geformt haben. Der Schwerpunkt der Studie konzentriert sich aufdie Frage nach dem Schema, das die Selbstversorgungssysteme (Weidewirtschaft und Ackerbau) langfristig mit den vielfaltigen demographischen, sozio-okonomischen und politischen Variablen verflechtet, um eine so dicht besiedelte "Insel" innerhalb des Seengebietes von Zentralafrika zu schaffen. Auf Landschaftsund Siedelungsveranderungen, die durch landwirtschaftliche und okonomische Entwicklungspolitik, Naturressourcen-Management und demographisches Wachstum verursacht wurden, wird besonders eingegangen. Eine wichtige Frage stellt sich: Wird Rwanda als Antwort auf beschleunigtes Bevolkerungswachstum sich in Richtung eines landwirtschaftlichen "Riickgangs" oder einer "Intensivierung" bewegen? Schlufifolgerungen beziiglich kiinftiger Beziehungen zwischen Bevolkerung und Ressourcen werden gemacht.