Fate of Heavy Metals in an Urban Natural Wetland: The Nyabugogo Swamp (Rwanda)

The Nyabugogo natural wetland (Kigali City, Rwanda) receives all kinds of untreated wastewaters, including those from industrial areas. This study monitored heavy metal concentrations (Cd, Cr, Cu, Pb, and Zn) in all environmental compartments of the swamp: water and sediment, the dominant plant species Cyperus papyrus, and fish (Clarias sp. and Oreochromis sp.) and Oligochaetes. Cr, Cu, and Zn concentrations in the water were generally below the WHO (2008) drinking water standards, whereas Cd and Pb were consistently above these limits. Except Cd, all metal concentrations were below the threshold levels for irrigation. The highest metal accumulation occurred in the sediment with up to 4.2 mg/kg for Cd, 68 mg/kg for Cu, 58.3 mg/kg for Pb, and 188.0 mg/kg for Zn, followed by accumulation in the roots of C. papyrus with up to 4.2 mg/kg for Cd, 45.8 mg/kg for Cr, 29.7 mg/kg for Cu, and 56.1 mg/kg for Pb. Except Cu and Zn, other heavy metal (Cd, Cr, and Pb) concentrations were high in Clarias sp., Oreochromis sp., and Oligochaetes. Therefore, there is a human health concern for people using water and products from the swamp.     

卢旺达共和国山地丘陵区土壤侵蚀调查报告

[目的]在卢旺达山地丘陵区开展土壤侵蚀调查,分析该区土壤侵蚀特征及成因,为尼罗河上游山地丘陵区土壤侵蚀预报和水土流失防治提供科学依据。[方法]在卢旺达布设4条调查路线并选择调查点,于2019年10月17—22日对调查点土壤侵蚀特征、成因及水土保持措施等进行了调查。[结果]卢旺达多山地且以农牧业为主,土壤侵蚀主要发生在坡耕地、损毁林地、建设用地等。坡耕地以片蚀和细沟侵蚀为主。损毁林地以片蚀和细沟侵蚀为主,部分出现沟蚀;当裸露地表形成草地或幼林后均较少发生土壤侵蚀。公路边坡、开挖边坡、土路路面及边坡等在降雨及径流的作用下产生沟蚀,部分路段偶有勤侵蚀发生。梯田是该国最主要的水土保持措施,具有较好的生态和经济效益。[结论]卢旺达土壤侵蚀主要以水力侵蚀为主,重力侵蚀次之。不合理的开垦坡地、毁林,加之多山的地形,导致侵蚀较为严重,威胁当地的生态安全及粮食安全。该区缺乏水土流失监测资料,需要重视水土保持基础理论研究,加强水土流失基础数据的监测和采集,同时需要加强其水土保持措施及土地管理工作,保障卢旺达农业的可持续绿色发展。     

Early growth of alley shrubs in the Highland region of Rwanda

Early growth of some woody shrubs used in alley cropping were studied in the Buberuka Highland and Central Plateau region of Rwanda. The altitudinal ranges for the two agroecological zones are 1800–2400 m and 1500–1900 m respectively. First, early growth of Sesbania sesban (Sesbania) as affected by intercropped bean, potato, pea and wheat was studied. Second, effect of lime and manure applications on growth of Sesbania, Leucaena sp (Leucaena), Calliandra Calothyrsus (Calliandra) and Markhamia lutea (Markhamia) was investigated. Third, growth of Sesbania and Leucaena at selected locations were examined. Bean grown in association with Sesbania enhanced the growth of the shrub in the Central Plateau region. At both sites, growth of Sesbania was retarded by intercropped pea. Growth of Sesbania increased significantly during the dry season in June and July. Biomass and height after one years' growth of Sesbania were higher in the Buberuka than in the Central Plateau region. Growth of the shrubs is ranked as: sesbania > Leucaena > Calliandra > Markhamia in the Buberuka Highlands. Farmyard manure generally increased the growth rates of the shrubs. Calliandra and Leucaena were most responsive to liming. The response of Leucaena to liming decreased with manure application but no definite trend was observed for Calliandra, Sesbania and Markhamia. Sesbania and Markhamia were least influenced by application of lime. Their respective LRI's were 0.35 and 0.46. The average growth rates for Sesbania and Leucaena at selected locations ranged between 26.4–62.2 cm/month and 13.1–27.4 cm per month respectively.Contribution from the University of Arkansas' USAID supported Farming Systems Research Program (FSRP) in Rwanda (USAID 696-0110), BP 625, Kigali Rwanda