UNESCO/UNITWIN WiCop Master in Water and Coastal Management Aulario Norte Campus Puerto Real E-11519 Tel. +34-956-016764. Fax: +34-956-016780 [email protected] http://www.uca.es/internacional/ Nutrient budget in a water body: A case study of Lake Victoria 1&2 Nancy Awuor Oduor 1. Universidad de Cadiz, Spain. Department of Marine Science 2. Kenya Marine and Fisheries Research Institute (KMFRI), Mombasa, Kenya. Description of the study area Lake Victoria is the largest African lake and second largest in the world, second after Lake Superior, with a surface area of 68,800 km2 and an adjoining catchment of 184,000 km2. The lake is located between latitudes 0o30' N and 2o30' S and longitudes 31o50' E 34o10' E touching the Equator in its northern reaches lying at an altitude of 1135m. It is relatively shallow with an average depth of about 40m reaching a maximum depth of about 81m. The lake’s shoreline is about 3,440km long enclosing numerous small and shallow bays and inlets several of which are composed of swamps and wetlands. The lake is shared among three countries namely Kenya, Uganda and Tanzania. Water inflow and outflow of the lake is dominated by rainfall and evaporation accounting for about 85% in each case. The remaining outflow is through White Nile River which is the only distributary of the lake while the rest 15% inflow is supplied by streams, runoffs and rivers dominated by Kagera River. Other tributaries are Sio, Nzoia, Yala, Nyando, Sondu Miriu, Mogusi and Migori rivers (Gichuki et al, 2005). Three ecoregions surrounds the lake namely; hills and plateaus, bush-lands and thickets and densely forested woodlands. The lake provides major ecosystem services namely including high biological diversity, fringing wetlands and flood plain vegetation. Figure 1: Lake Victoria Basin. (Source: Robert Simmonin, USDA Foreign Agricultural Service) Lake Victoria is a vital resource on which about 30 million people in the riparian countries are dependent. The lake is used as a source of food, energy, industrial, domestic and irrigation water, building materials and transportation as well as a repository for industrial, agricultural and domestic waste. The catchment area hosts several cities and towns which are densely populated and characterized with several industries, factories and informal settlement with poor waste management practices. Unmanaged solid and liquid wastes together with atmospheric and diffuse agricultural sources contributes to large amounts of nutrients supplied to the lake causing eutrophication. This has in turn caused water pollution, biodiversity loss, land degradation, and damage to wetlands. It is therefore due to this unmanaged supply nutrients that this study is conducted aimed at determining nutrient budget of the lake. This is done through identification of major sources of the nutrients inflows and the possible ways these nutrients are utilized/out flown based on existing literature and class theoretical study. Nutrient (Nitrogen, N, and Phosphorus, P) loading of the Lake: Previous studies in the lake shows that its trophic status ranged from oligotrophic to mesotrophic to eutrophic with increasing supply of nutrients and organic matter. This is evidenced in the array of symptomatic changes that has been stimulated including; increased phytoplankton and macrophytes production, fisheries and water quality deterioration and other undesirable changes that interfere with water uses. The major sources of nutrients to the lake are discussed below. Major Sources of nutrients: Atmospheric deposition: This together with land run off are the major nutrient inputs in the lake accounting for approximately 90% of phosphorous and 94% of nitrogen (COWI, 2002). Scheren (1995) suggests that the increase in P and N is primarily due to increases in atmospheric deposition from biomass and forest burning; and wind erosion which have increased the atmospheric loading and subsequent deposition. Clearing of vegetation through burning is a common practice to pave way for settlement and establishment of urban, infrastructure and agricultural developments. The use of fossil fuel and charcoal production in the energy sector also release massive amount of nitrogen and phosphorus oxides to the air which later gets into the water bodies through either wet or dry deposition. It is therefore clear that as population increases more land is cleared leading to more supply of these nutrients in the atmosphere. Agriculture: Fertilizer and chemical leaching, runoff from agricultural fields, manure from concentrated livestock operations, and aquaculture are the largest agricultural nutrient sources. Chemical fertilizers and animal manure are often applied in excess of crop needs in the region (MA 2005); the excess nutrients are then lost through volatilization, surface runoff, and leaching to water bodies. Increased land clearing and poor farming methods like overstocking have led to vulnerability of the soils to erosional agents; sedimentation and nutrient run off is high with erosio rate a d sedi e t loads i so e ri ers’ rea hi g 300 to s / K o ser ed. Bullock et al., (1995) estimated that 50% of the nitrogen input and 56% of the phosphorous input is due to runoff from agricultural land. Municipal/ Urban Sources: About 87 large towns are found in the lake basin (51 in Kenya, 30 in Tanzania and 6 in Uganda), COWI, 2002. Municipal wastewater treatment plants and industrial wastewater discharges, nitrogen leaching from below-ground septic tanks, and storm-water ru off are so e of the ur a a d i dustrial sour es of utrie ts. They are ajorly fro poi t sour es dis harged dire tly to surfa e aters or grou d ater ia pipes or other dis rete conveyance. Discharging of raw sewage or poor quality effluents into the rivers and lakes have been noted to be due to lack of sustainable waste treatment or malfunctional facilities in the area. The study by Bullock et al., (1995) as well estimated that 30% of N and P is from rural domestic waste, and 10-15% due to urban waste with the rural wastes mainly from diffuse sources. Storm-water runoff is another significant source of nutrients from urban areas. Rainfall events flush nutrients from residential lawns and impervious surfaces into nearby rivers and streams through combined sewers or separate channels. The combined sewer overflows often causes release of raw untreated effluents with high nutrient and organic loads into the water bodies during heavy rains when the volume is exceeded. The addition of some 40,000 human corpuses-war causalities that floated down the Kagera River in May 1994 from Rwanda as well led to the lakes nourishment (LVEMP, 2003). Industrial sources: There are about 68 industries in the catchment site (16 in Kenya, 34 in Tanzania and 18 in Uganda) contributing to point sources of nutrients. These include pulp and paper mills, direct discharge of sewage from maritime vessels and agro based industries like meat, sugar, coffee, tea, dairy, fish, tanneries which discharge semi treated effluents and other industrial wastes and run offs with high nutrients in the lake. Table 1: Annual Nutrient loading/inputs to Lake Victoria (Source: LVEMP, 2003) Nutrient pathway and catchment vulnerability: Nutrient transfer comprise of transportation of organic and inorganic suspended solids and dissolved nutrients carried by streams, terrestrial dust from wind erosion, inorganic compounds in the smoke. These enter aquatic ecosystems via the air, surface water or ground water. The major nutrient inputs are listed in Table 1 above. The main out puts are through atmospheric loss, sediment deposition, River water and resource harvested (See Figure 2 below). Point and diffuse nutrient source: Atmospheric deposition, land use export, Industrial, municipal and agricultural releases, rivers and streams run-offs. Discharges etc. Lake Victoria Basin River outputs: Retention Resource harvests (Fish, plant, soils etc.); Atmospheric losses. Sediment burial Sediment release Figure 2: Nutrient budget in Lake Victoria Basin Vulnerability to eutrophication: The Lake’s topography a d the at h e t’s gro i g population density makes it vulnerable to eutrophication. As the population grows, pressures on the productive capacity of agriculture and industry; intensive agriculture and land use conversion for crops, livestock and aquaculture; and energy consumption increases too leading to deforestation and use of more fossil fuels. Poor management practices witnessed in poor agricultural and waste management operations is another issue making the area threatened. Effect of climate change on nutrient loading: Climate change and the potential related warming can change runoff, nutrient transport, mean wind velocities and water temperatures. Current studies project an increasing precipitation in the region an issue which will increase the surface runoff leading to more nutrient washing and supply to the lake. The increasing temperature regime as well increases decomposition and transformation (respiration, mortality, grazing and sedimentation) rate of many organic materials in the catchment facilitating rapid release of nutrients to the environment. Moreover, rising temperatures have been observed to cause thermal stability due to reduction in wind speed in the lake hindering mixing of the water that supplies nutrients trapped in the deeper bottom waters sediments to the upper photic zones. This results to accumulation of these nutrients in the bottom sediments. Management: Currently, there are no agreed baseline management policies defining water quality/discharge standards among the three riparian countries sharing the lake. However, local and national authorities have their legislations defining the discharged effluent standards that is less harmful to the lakes ecology. The industrial and domestic wastes are therefore expected to be treated before being released to the environment a precaution that have been implemented by some institutions and industries but neglected by many. The rural communities are also required to collect and manage their wastes. Conclusion: The increase in human population is the major threat to the lakes ecosystem, this is due to the observed increasing activities carried to meet the rising demand resulting to eutrophication and hypoxia. Lack of better management and climate change also poses threats to the lake that is likely to suffer irreversible environmental damage. There is need for the governments to collectively create and strictly observe policies that ensure the lakes sustainability including restoration and preservation of the lake's ecosystem; they should therefore be directed towards improved land-use practices and a control over land clearing, forest burning and improved sanitary and industrial waste treatments. Education and awareness campaigns are also necessary for the public about the lakes importance and threats. Relevant Literature 1. Bullock S., Mooney H., (1995). Seasonally dry Tropical Forests, Cambridge UK. 2. COWI Consulting Engineers (2002). Integrated Water Quality/Limnology Study for Lake Victoria. Lake Victoria Management Project, Part II Technical Report. 3. Gichuki NN, Oyieke HA, Terer T (2005). Status and root causes of biodiversity loss in the Eastern Rift Valley Lakes, Kenya. Nairobi, Kenya, 4. Kendall, R. L. 1969. An ecological history of the Lake Victoria Basin. Ecol. Monogr. 39: 121-176. 5. LVEMP, 2003. Lake Victoria Environmental Management Phase 1, Revised Draft scientific Report, World Bank: Washington DC. 6. Millennium Ecosystem Assessment (MA). 2005. Ecosystems and Human Wellbeing: Policy Responses Volume 3. Chapter 9: Nutrient Management: pp. 295-311. Primary Authors: Howarth, R. and K. Ramakrrshna. Eds. K. Chopra, R. Leemans, P. Kumar, and H. Simons. Washington, DC: Island Press. 7. R. E. Hecky (1993). "The eutrophication of Lake Victoria". Verhandlungen der Internationale Vereinigung für Limnologie 25: 39–48. 8. Rutherford K, Palliser C, Wadhwa S, (2009). Nitrogen exports from the Lake Rotorua catchment - calibration of the ROTAN model. NIWA Client report. HAM2009-019. Jan 2009 revised April 2009 9. Scheren P. A. (2001). Assessment of pollution sources and socio-economic activities related to Eutrophication in Lake Victoria, LVEMP Presentation: Kisumu, Kenya.