Lake Victoria: will it support life tomorrow? A case for abatement of pollution and eutrophication of fresh waters. Item Type Book Section Authors Wandiga, S.O.; Madadi, V.O.; Kirimire, B.T.; Kishimba, M. Publisher United Nations Environment Programme (UNEP), Pan African START Secretariat (PASS) Download date 27/09/2021 05:16:12 Link to Item http://hdl.handle.net/1834/7363 Lake Victoria: will it support life tomorrow? A case for abatement of pollution and eutrophication of fresh waters Shem O. Wandiga*14∗a, Vincent O. Madadib, Bernard T. Kirimireb and Michael Kishimbac aDepartment of Chemistry, University of Nairobi, P.O. Box 30197, Nairobi, Kenya bDepartment of Chemistry, Makerere University, P.O. Box 7062, Kampala, Uganda cDepartment of Chemistry, University of Dar es Salaam, P.O. Box 35097, Dar es Salaam, Tanzania ABSTRACT The decline in the quality of water has been associated with human activities in both the catchments and near shore areas. The poor quality of Lake Victoria’s water is a result of discharges of untreated sewer and chemical wastes from urban centres as well as microbacterial and nutrient laden runoffs from pastoral agricultural land, shrub-lands, forests and municipal slums. The deterioration of Lake Victoria’s ecology is linked to the rapid riparian population growth and consequent livelihood activities associated with farming and urbanization. The review demonstrates that the Lake’s water quality has deteriorated to a point that it is no longer able to support aquatic life in the same way it did 40 years ago. The major driving force behind water quality deterioration is population increase. Deforestation, poor agricultural practices, over-stocking and grazing have all contributed to massive soil erosion that continues to convey sediments to the lake. The establishment of institutions that will encourage stakeholder participation in conservation and management of resources at the village, local, national and regional levels is essential for the sustainable utilization of the Lake’s resources. The riparian governments need to show both political will and policy direction through establishing policies that engage the public, and enforce existing rules and regulations that will address the water pollution concerns. Keywords: Lake Victoria, pollution, eutrophication, sedimentation, phosphorous, Nitrogen, BOD, heavy metals, pesticides INTRODUCTION Lake Victoria has one of the most beautiful and scenic watersheds surrounded by hills on most sides (Figure 1). The lake water is a source of food, energy, drinking and irrigation water, shelter, transport, and serves as a repository for human, agricultural and industrial waste. It has several islands which form the habitats of several bird species, reptiles, other water and land animal species as well as indigenous trees and plant species. The cichlid fish species were estimated to number over 500 in the 1960s, however, recent inventories show these numbers to have appreciably declined (Verschuren and others 2002; Barel and others 1985; Ogutu-Ohwayo 1990; Witte and others 1992). 14 ∗Corresponding Author, E-mail: [email protected] Figure 1: A beautiful sunset over L. Victoria (Photo: S.O. Wandiga). The decline in the quality of water has been associated with human activities in both the catchments and near shore areas. Historical monitoring data are scarce and hamper apportioning of responsibilities. Furthermore, the dynamic and complex nature of ecosystem changes have not been delineated to allow assessment of the impacts of catchment changes on the lake. What is apparent is that the onset of massive cyanobacteria blooms offshore took place at the same time the indigenous fish stock collapsed. The association of Nile perch (Lates niloticus (Centropomidae)) population bloom and decimation of plankton eating haplochromine cichlids (Ochumba and Kibaara 1989; Goldschmidt and others 1993) should be extended to include the cause-effect relationship between the nutrient load pollution of the lake and alien species introduction. Deforestation coupled with poor agricultural practices have led to an accelerated rate of sedimentation. The high sedimentation rate has been contributed mostly by Kenyan rivers and by Kagera River receiving its waters from Rwanda, Burundi, Democratic Republic of Congo, Uganda and Tanzania. The quality of Lake Victoria’s water further suffers a double tragedy by receiving large discharges of untreated sewer and chemical wastes from urban centres as well as microbacterial and nutrient laden runoffs from pastoral agricultural land, shrub-lands, forests and municipal slums. Pesticides have been introduced either directly by fishermen or indirectly through runoff from agricultural areas. Recent evidence indicates that mining activities along the shoreline or upstream may be introducing toxic cyanide and mercury into the lake (Campbell 2000). The beginning of the slow deterioration of Lake Victoria’s ecology is very much linked to the rapid riparian population growth and consequent livelihood activities associated with farming and urbanization. The Lake Victoria Basin (LVB) now supports one of the densest and poorest rural populations in the world (Figure 2). The population has increased from an estimated 3 million in 1890 to 4.6 million in 1932 and stood at 27.7 million by 1995 (United Nations 1995). With the populations of the riparian communities growing at rates that are among the highest in the world (around 3% per year), the multiple activities in the lake basin have increasingly come into conflict with the lakes’ ability to cope. Recent population census’ show declining growth rates due to the HIV/AIDS pandemic and other diseases. However the rate still remains among the highest in the world (around 2.7% per year) and the populations in the five riparian countries are expected to double again over the next 25-35 years and is estimated to reach 53 million by 2020 (United Nations 1995). Lake Victoria, directly or indirectly, supports 28 million people who produce an annual gross economic product in the order of US$ 3-4 billion (or 107–143 $US GDP per capita). Over the 1965-95 period the per capita income levels in Kenya, for example, averaged 2.4% ± 2.6% (95% CI) per annum (World Bank 1998). The Welfare Monitoring Survey implemented in Kenya in 1994 further shows that the incidence of “hard core” poverty was between 40% and 50% in three Lake Basin districts (Bungoma, Busia and Kericho) and between 30% and 40% in four Lake Basin districts (Bomet, Nyamira, Vihiga and Kakamega) (Republic of Kenya 1996; Republic of Kenya 2002a,b). Hard core poverty was defined as total expenditure of less than Ksh 703 per adult equivalent per month, and is thus a much stricter standard than the dollar-a-day rule used by the World Bank. The poverty levels in all the riparian countries are similar to that in Kenya. EUTROPHICATION AND ITS CAUSES The quality of the lake water has deteriorated in several respects (Hecky and Bugenyi 1992). The lake depth, bottom oxygen content and transparency (the Secchi index decreased from 5m in 1930 to less than 1m in 1990s) have decreased, while sediment and water phosphorus and nitrogen concentrations have increased (Hecky 1993). Hence the lake bottom is eutrophicated during some seasons of the year. Consequently, strong remediation measures are required to improve municipal sewerage treatment plants, reforest deforested lands, improve agricultural practices and enforce existing laws and regulations at the national and regional levels. There is need to establish new laws, regulations and institutions to manage the lake. Several factors including unchecked soil erosion, municipal and rural wastes as well as residues cause the increase in pollution of the lake from agricultural and other economic activities around the lake. Figure 2: Principal events in the recent environmental history of Lake Victoria, in relation to human-population growth and agricultural production in its drainage basin (Verschuren and others 2002). Soil erosion, sedimentation and nutrient loading As the riparian population increased so did the need to grow more food. The expansion of agricultural land necessitated clearing of land and deforestation. Furthermore, bad agricultural practices like cultivating on slopes and river beds have caused massive soil erosion. Increased nutrient flows into the lake coming mostly from agricultural land and forest areas have been estimated to range between 69 x 107 kg/yr to 1.98 x 1010 kg/yr (Verschuren and others 2002) with resultant plume expansion in the lake (Figures 2, 3). The lake receives 2.3 mm per year of sediment load (silt, P, N and others) (Odada and others 2003; Verschuren and others 2002). Paleolimnological evidence show that most of the land changes and hence sediment deposits occurred after 1940 with the heaviest deposits occurring between 1970 and the early 1980s. The paleolimnological data established a strong chronological link between historical land use and algal production in the lake (Verschuren and others 2002). Therefore, it may be concluded that landscape disturbance rather than food-web alteration or climate change is the dominant cause of the ongoing eutrophication. The high sediment load has brought into the lake high nutrient loads that feeds the water hyacinth (Figure 3). The rivers in the catchments are the carriers of both sediment and nutrient loads choking the lake. Table 1 gives the rivers and their sediment capacity indices. It is evident that some rivers like Rivers Nyando and Kagera are more prominent in their share of sediment and nutrient deposits. This is because of their percent slope and volume of water carried. The action of Kenya, Rwanda, Burundi and the Democratic of Congo in preventing upstream soil erosion are very critical to the saving of Lake Victoria. This does not exempt Uganda and Tanzania from sharing their responsibility in soil management. Figure 3: Satellite image depicts a green plume of nutrient rich sediment flowing into Lake Victoria (Photo Courtesy, ICRAF). Table 1: Biophysical characteristics of Lake Victoria basin (Shepherd and others 2000). Ave. est.