Eutrophication and nutrient release in urban areas of sub-Saharan Africa--a review.

Eutrophication is an increasing problem in sub-Saharan Africa (SSA), and, as a result, the ecological integrity of surface waters becomes compromised, fish populations become extinct, toxic cyanobacteria blooms are abundant, and oxygen levels reduce. In this review we establish the relationship between eutrophication of fresh inland surface waters in SSA and the release of nutrients in their mega-cities. Monitoring reports indicate that the population of mega-cities in SSA is rapidly increasing, and so is the total amount of wastewater produced. Of the total amounts produced, at present, less than 30% is treated in sewage treatment plants, while the remainder is disposed of via onsite sanitation systems, eventually discharging their wastewater into groundwater. When related to the urban water balance of a number of SSA cities, the total amount of wastewater produced may be as high as 10-50% of the total precipitation entering these urban areas, which is considerable, especially since in most cases, precipitation is the most important, if not only the 'wastewater diluting agent' present. The most important knowledge gaps include: (1) the fate and transport mechanisms of nutrients (N and P) in soils and aquifers, or, conversely, the soil aquifer treatment characteristics of the regoliths, which cover a large part of SSA, (2) the effect of the episodic and largely uncontrolled removal of nutrients stored at urban surfaces by runoff from precipitation on nutrient budgets in adjacent lakes and rivers draining the urban areas, and (3) the hydrology and hydrogeology within the urban area, including surface water and groundwater flow patterns, transport velocities, dynamics of nutrient transport, and the presence of recharge and discharge areas. In order to make a start with managing this urban population-related eutrophication, many actions are required. As a first step, we suggest to start systematically researching the key areas identified above.

[1]  A. Roychoudhury,et al.  Phosphorus dynamics in shallow eutrophic lakes: an example from Zeekoevlei, South Africa , 2009, Hydrobiologia.

[2]  R. Thunvik,et al.  Study of the impact of land use and hydrogeological settings on the shallow groundwater quality in a peri-urban area of Kampala, Uganda. , 2007, The Science of the total environment.

[3]  S. Pflugmacher,et al.  Ecotoxicological effects of selected cyanobacterial secondary metabolites: a short review. , 2005, Toxicology and applied pharmacology.

[4]  David Love,et al.  ASSESSMENT OF THE IMPACTS OF PIT LATRINES ON GROUNDWATER QUALITY IN RURAL AREAS: A CASE STUDY FROM MARONDERA DISTRICT, ZIMBABWE , 2006 .

[5]  D. Dixon,et al.  Trophic Niche Segregation in the Nilotic Ichthyofauna of Lake Albert (Uganda, Africa) , 2005, Environmental Biology of Fishes.

[6]  M. Nola,et al.  Eutrophication of lakes in urbanized areas: The case of Yaounde Municipal Lake in Cameroon, Central Africa , 2006 .

[7]  T. Datry,et al.  Dynamics of solutes and dissolved oxygen in shallow urban groundwater below a stormwater infiltration basin. , 2004, The Science of the total environment.

[8]  M. Munawar,et al.  The Great Lakes of the World (GLOW): Food-Web, Health and Integrity , 2001 .

[9]  J. Faillat.  Origine des nitrates dans les nappes de fissures de la zone tropicale humide — Exemple de la Côte d'Ivoire , 1990 .

[10]  I. Nhapi,et al.  A proposal for managing wastewater in Harare, Zimbabwe , 2006 .

[11]  I. Douglas,et al.  Unjust waters: climate change, flooding and the urban poor in Africa , 2008 .

[12]  B. Allanson,et al.  Part II An introduction to the limnology of Hartbeespoort Dam with special reference to the effect of industrial and domestic pollution , 1961, Hydrobiologia.

[13]  Programme United,et al.  UN-Habitat. The Challenge of Slums: Global Report on Human Settlements, . Human Settlements, London: Earthscan Publications, . , 2003 .

[14]  R. Thunvik,et al.  Phosphorus transport in shallow groundwater in peri-urban Kampala, Uganda: results from field and laboratory measurements , 2008 .

[15]  C. Figueredo,et al.  Seasonal variation in the diversity and species richness of phytoplankton in a tropical eutrophic reservoir , 2001, Hydrobiologia.

[16]  J. Munro.  A limnological survey of Lake McIlwaine, Rhodesia , 1966, Hydrobiologia.

[17]  T. Mkandawire.  Quality of groundwater from shallow wells of selected villages in Blantyre District, Malawi , 2008 .

[18]  S. Uhlenbrook,et al.  Transport of Escherichia coli and solutes during waste water infiltration in an urban alluvial aquifer. , 2008, Journal of contaminant hydrology.

[19]  K. Strzepek,et al.  Water Quality Assessment and Modeling of an Effluent-Dominated Stream, the Notwane River, Botswana , 2005, Environmental monitoring and assessment.

[20]  H. Golterman,et al.  Eutrophication of Lakes, Rivers and Coastal Seas , 1991 .

[21]  S. Alagbe.  Preliminary evaluation of hydrochemistry of the Kalambaina Formation, Sokoto Basin, Nigeria , 2006 .

[22]  P. Ashton,et al.  Aspects of the phosphorus cycle in Hartbeespoort Dam (South Africa) Phosphorus loading and seasonal distribution of phosphorus in the reservoir , 1989, Hydrobiologia.

[23]  Jean-Louis Perrin,et al.  Spatial evolution of nitrogen and phosphorus loads along a small Mediterranean river: implication of bed sediments , 2005 .

[24]  G. D. Villiers,et al.  The water quality of a small urban catchment near Durban, South Africa , 1985 .

[25]  M. H. Barrett,et al.  Temporal variations in the depth-specific hydrochemistry and sewage-related microbiology of an urban sandstone aquifer, Nottingham, United Kingdom , 2003 .

[26]  T. Bere.  The assessment of nutrient loading and retention in the upper segment of the Chinyika River, Harare: Implications for eutrophication control , 2009 .

[27]  M. Nola,et al.  Dynamic of phytoplankton size-class and photosynthetic activity in a tropical hypereutrophic lake: the Yaounde municipal lake (Cameroon) , 2009, Hydrobiologia.

[28]  J. Talling.  Environmental regulation in African shallow lakes and wetlands , 1992 .

[29]  M. Tijani,et al.  Assessing the basement aquifers of Eastern Senegal , 2008 .

[30]  Steve Pedley,et al.  Urbanisation effects on groundwater chemical quality: findings focusing on the nitrate problem from 2 African cities reliant on on-site sanitation. , 2007, Journal of water and health.

[31]  E. Kebede-Westhead,et al.  Long-term changes in chemical features of waters of seven Ethiopian rift-valley lakes , 2002, Hydrobiologia.

[32]  M. Kirkby,et al.  Man-made lakes , 1967 .

[33]  J. Talling.  ORIGIN OF STRATIFICATION IN AN AFRICAN RIFT LAKE , 1963 .

[34]  D. Lerner,et al.  Non-agricultural sources of groundwater nitrate: a review and case study. , 2005, Water research.

[35]  J. Thornton.  Assessment and control of nonpoint source pollution of aquatic ecosystems : a practical approach , 1999 .

[36]  G. K. Anornu,et al.  Hydrogeochemical evaluation of groundwater in the lower Offin basin, Ghana , 2008 .

[37]  F. Kansiime,et al.  A simulation model for nitrogen retention in a papyrus wetland near Lake Victoria, Uganda (East Africa) , 2007, Wetlands Ecology and Management.

[38]  Un-Habitat.  The Challenge of Slums: Global Report on Human Settlements 2003 , 2004 .

[39]  Israela Ravina,et al.  Irrigation with treated sewage effluent : management for environmental protection , 1991 .

[40]  N. Moyo.  Lake Chivero: A Polluted Lake , 1997 .

[41]  C. Ptacek,et al.  Geochemical stability of phosphorus solids below septic system infiltration beds. , 2004, Journal of contaminant hydrology.

[42]  I. Nhapi.  Inventory of water management practices in Harare, Zimbabwe , 2008 .

[43]  A.M.C. Lemmens,et al.  Estimation of water pollution sources in Lake Victoria, East Africa: Application and elaboration of the rapid assessment methodology , 2000 .

[44]  O. Fatoki,et al.  Situation analysis of water quality in the Umtata River catchment , 2001 .

[45]  C. Neal,et al.  Sewage-effluent phosphorus: a greater risk to river eutrophication than agricultural phosphorus? , 2006, The Science of the total environment.

[46]  A. Lawrence,et al.  Groundwater evolution beneath Hat Yai, a rapidly developing city in Thailand , 2000 .

[47]  T. E. Cloete,et al.  An overview of toxic freshwater cyanobacteria in South Africa with special reference to risk, impact and detection by molecular marker tools , 2006 .

[48]  Oladele Osibanjo,et al.  Evaluation of Groundwater Quality Characteristics near Two Waste Sites in Ibadan and Lagos, Nigeria , 2002 .

[49]  H. A. Rutjes,et al.  Major morphological changes in a Lake Victoria cichlid fish within two decades , 2008 .

[50]  R. Hecky,et al.  The eutrophication of Lake Victoria , 1993 .

[51]  F. Kansiime,et al.  Nutrient status and retention in pristine and disturbed wetlands in Uganda: management implications , 2007, Wetlands Ecology and Management.

[52]  A. Edet,et al.  Hydrogeological and hydrochemical character of the regolith aquifer, northern Obudu Plateau, southern Nigeria , 2005 .

[53]  M. H. Barrett,et al.  On-site sanitation and urban aquifer systems in Uganda , 1999 .

[54]  J. G. O'neill,et al.  Biological, chemical and physical drinking water quality from shallow wells in Malawi: Case study of Blantyre, Chiradzulu and Mulanje , 2007 .

[55]  R. Devi,et al.  Assessment of siltation and nutrient enrichment of Gilgel Gibe dam, Southwest Ethiopia. , 2008, Bioresource technology.

[56]  R. Robarts.  Heterotrophic bacterial activity and primary production in a hypertrophic African lake , 1988, Hydrobiologia.

[57]  P. J. Chilton,et al.  Groundwater and its susceptibility to degradation : a global assessment of the problem and options for management , 2003 .

[58]  B. Kortatsi.  Hydrochemical framework of groundwater in the Ankobra Basin, Ghana , 2007 .

[59]  H. Aalderink,et al.  Simulation of pollution buffering capacity of wetlands fringing the Lake Victoria. , 2003, Environment international.

[60]  J. G. O'neill,et al.  Assessment of groundwater quality in shallow wells within the southern districts of Malawi , 2008 .

[61]  C. M. Iwegbue,et al.  Water quality changes in relation to Diptera community patterns and diversity measured at an organic effluent impacted stream in the Niger Delta, Nigeria , 2007 .

[62]  Frank Kansiime,et al.  Comparative assessment of the value of papyrus and cocoyams for the restoration of the Nakivubo wetland in Kampala, Uganda , 2005 .

[63]  S. Loiselle,et al.  Relationships between wetland ecotones and inshore water quality in the Ugandan coast of Lake Victoria , 2007, Wetlands Ecology and Management.

[64]  J. Talling.  The photosynthetic activity of phytoplankton in East African lakes , 1965 .

[65]  J. Thornton.  Aspects of the phosphorus cycle in Hartbeespoort Dam (South Africa) , 1989, Hydrobiologia.

[66]  K. Uma.  Nitrates in shallow (regolith) aquifers around Sokoto Town, Nigeria , 1993 .

[67]  E. Brown,et al.  History and timing of human impact on Lake Victoria, East Africa , 2002, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[68]  S. Efe.  Quality of Water from Hand Dug Wells in Onitsha Metropolitan Areas of Nigeria , 2005 .

[69]  Y. Gélinas,et al.  Well water survey in two districts of Conakry (Republic of Guinea), and comparison with the piped city water , 1996 .

[70]  T. E. Cloete,et al.  Bacterial and chemical quality of water supply in the Dertig village settlement , 1999 .

[71]  B. Kortatsi.  Hydrochemical characterization of groundwater in the Accra plains of Ghana , 2006 .

[72]  F. Kansiime,et al.  The role of sediments for phosphorus retention in the Kirinya wetland (Uganda) , 2007, Wetlands Ecology and Management.

[73]  R. Mugidde.  The increase in phytoplankton primary productivity and biomass in Lake Victoria (Uganda) , 1993 .

[74]  M. Burgis,et al.  The Ecology and utilization of African inland waters , 1981 .

[75]  T. E. Cloete,et al.  Biological and chemical evaluation of sewage water pollution in the Rietvlei nature reserve wetland area, South Africa. , 2008, Environmental pollution.

[76]  C. Magadza,et al.  Lake Chivero: A management case study , 2003 .

[77]  D. Ophori,et al.  Hydrogeological and hydrochemical characterization of the Voltaian Basin: the Afram Plains area, Ghana , 2008 .

[78]  R. Dorit,et al.  Destruction of fisheries in Africa's lakes , 1985, Nature.

[79]  I. Nhapi,et al.  Sewage discharges and nutrient levels in Marimba River, Zimbabwe , 2004 .

[80]  A. Navarro,et al.  Evaluation of groundwater contamination beneath an urban environment: the Besòs river basin (Barcelona, Spain). , 2007, Journal of environmental management.

[81]  J. Roos,et al.  Causes and consequences of algal blooms in Loch Logan, an urban impoundment , 2007 .

[82]  L. Kaufman,et al.  Deoxygenation of the deep water of Lake Victoria, East Africa , 1994 .

[83]  A. Roychoudhury,et al.  Elemental (C, N, H and P) and stable isotope (δ15N and δ13C) signatures in sediments from Zeekoevlei, South Africa: a record of human intervention in the lake , 2008 .

[84]  W. Taylor,et al.  Seasonality and spatial variation in abundance, biomass and activity of heterotrophic bacterioplankton in relation to some biotic and abiotic variables in an Ethiopian rift‐valley lake (Awassa) , 1989 .

[85]  H. Kloos,et al.  Urban impact on ecological integrity of nearby rivers in developing countries: the Borkena River in highland Ethiopia , 2009, Environmental monitoring and assessment.

[86]  B. Morris,et al.  Assessing the impact of modern recharge on a sandstone aquifer beneath a suburb of Doncaster, UK , 2006 .

[87]  P. Ashton,et al.  The influence of a toxic cyanobacterial bloom and water hydrology on algal populations and macroinvertebrate abundance in the upper littoral zone of Lake Krugersdrift, South Africa , 2009, Ecotoxicology.

[88]  David Love,et al.  Effects of a semi-formal urban settlement on groundwater quality: Epworth (Zimbabwe): Case study and groundwater quality zoning , 2005 .