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LAKE VICTORIA - AN INTRODUCTION

by: Keith D. Shepherd

High Population Growth

The Lake Victoria Basin (LVB) now supports one of the densest and poorest rural populations in the world, with densities up to 1200 persons per square kilometre in parts of Kenya (Hoekstra and Corbett, 1995). The first systematic population surveys for Kenya, Tanzania and Uganda, were conducted during the late 1940’s. The 1948 estimate for Kenya, for example, is given at 5.7 million inhabitants (Lury, 1969). The current estimate is 28.4 million inhabitants giving an approximate population doubling time of 22.1 years. This means that the population of Kenya has doubled approximately 3.3 times in the time required for the water in Lake Victoria to turn over once. Moreover, population densities in the lake basin portions of Kenya, Tanzania, Uganda, Rwanda and Burundi are well above their respective national averages, indicating doubling times that are probably considerably shorter than the respective national averages.
National population growth rates, though declining due to the HIV/AIDS pandemic and other diseases, remain among the highest in the world and the populations in the five riparian countries are expected to double again over the next 25-35 years (UNPB, 2000). More specific projections and scenarios for Lake Victoria Basin are to our knowledge unavailable at this time. In the context of this project, these will be needed in order to provide realistic year 2050 land and water degradation scenarios based on which various management and policy options could be evaluated.

Related Resources

River Nyando Basin - an overview
Surveillance of Soil Erosion Phases
Surveillance of Soil Fertility Condition
Soil Degradation Risk Factors
Locating the Frontiers of Deforestation
Environmental Accounting of Resource Use and Degradation

High Levels of Poverty

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 GEP per capita). Over the 1965-95 period growth in per capita income levels in Kenya, for example, averaged 2.4% ± 2.6% (95% CI) per annum (World Bank Development Indicators, 1998). Even at the most optimistic end of this range (i.e., 5% growth per year), income doubling from 386 (in 1995) to 772 $US per capita (1984 eqv. U$) would be expected to take about 14 years. Under prevailing economic conditions, such a scenario seems highly unlikely, and even if it were to occur, Kenya would still rank in the lowest third of countries on a per capita income basis by current standards.
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). Hard core poverty was defined as total expenditure of less than Ksh 703 per adult equivalent per month (Central Bureau of Statistics, 1998) and is thus a much stricter standard than the dollar-a-day rule used by the World Bank. It is currently unknown how these figures will project to the future in a lake basin-wide context, and there is thus a need to collate income as well as other relevant poverty indicators in other parts the basin. Unfortunately, most such statistics are compiled at the national-level, and are generally difficult to disaggregate toward sub-national entities.
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Threats to Primary Production

The Lake produces about 170,000 metric tons of fish each year, with thousands of lakeshore residents employed in fishing and fish processing. Harvesting of Nile Perch (Lates niloticus), has generated about $US 100 million of foreign exchange in the past (Ayes et al., 1996) and there are about 10,000 people now employed at commercial fish processing facilities in the Kenyan towns of Kisumu, Homa Bay and Migori (Sunday Nation, April 11, 1999). The sustainability of the fishery is now threatened by: overfishing, pollution and uncertainty regarding ecological instability resulting from the introduction of the Nile Perch. Additional research regarding these threats will be needed to formulate long-term fisheries management strategies and policies. Subsistence agriculture, pastoralism and agro-pastoralism currently support about 21 million people in the basin (est. from data by Deichmann, 1994) with average incomes in the range of US$ 90-270 per annum (World Bank, 1996). In view of the pervasive poverty among farming communities in the basin (see above), the use of inorganic fertilizer is limited, and primary productivity is closely linked to the inherent productive capacity of the soil. Moderate soil erosion in the order of 5-10 t ha-1 yr-1, is associated with substantial losses in soil nutrients that contribute significantly to negative farm nitrogen, phosphorus and potassium balances (Van den Bosch et al. 1998, Shepherd and Soule, 1998). Depletion of soil fertility via biofixation and subsequent crop harvest, grazing, soil organic matter depletion and/or biomass burning exacerbate these problems and will not be resolved without the use of inorganic fertilizers. Perhaps the single greatest threat to primary production is the prevalence of land degradation as indicated by the decline in soil quality demonstrated in this report.

We therefore think it unlikely that fisheries, subsistence agriculture and extensive (agro)-pastoralism in their current forms will be able to support food and income requirements under the projected population doubling scenario over the next 25-35 years. Substantial investments in market infrastructure, roads, soil fertility recapitalization, education, fisheries management, conservation and human and veterinary healthcare will be necessary for sustainable intensification and economic growth in the region. It is currently unclear how such changes would be brought about, as it appears unlikely that these will be generated from within the agricultural and fisheries sectors in the foreseeable future.

Climatic Uncertainty

A number of paleoclimate studies have shown that long-term climate variability in the basin is periodic and tends to track events occurring over time periods that are characteristic of cyclical changes in orbital insolation and forcing (e.g., Kroll-Milankovitich cycles), and global ocean and atmospheric circulation (e.g. El Nino/La Nina cycles). Some of these studies (e.g. Stager et al., 1996) suggest that the post-1960 ecological shift in Lake Victoria may have had climate driven analogues over the last 10,000 years. This implies that although human impacts on the lake basin environment may now eclipse the events taking place, climate change could be reinforcing environmental degradation in the lake basin. (see project pictorials)
The more recent historical record shows the occurrence of an extraordinarily pluvial period from 1961-1964 in the eastern portion of the lake basin. During this time, the water level of Lake Victoria rose by approximately 2.5 meters, and discharges from rivers Nyando and Sondu Miriu, for example, were 10-20 times higher than their respective 35 year decadal averages. For the Nyando River Basin, interviews with local people suggest that many of the major soil erosion problems either started or were dramatically accelerated in their development during the early 1960’s. We speculate that rapid land use changes, deforestation, infrastructure development and over-grazing structurally altered this landscape during the first half of the 20th century. Prevailing conditions during the early 1960’s may then have been such that the basin was essentially primed for massive erosion/sedimentation during a period extraordinarily heavy rainfall in the region. Unfortunately, the current database does not allow us to estimate the return period of events of this magnitude, nor do we know how these affected sedimentation rates in the different river basins. This is of particular concern as we can only speculate what might happen now, should we witness the return of a rainfall period of the magnitude observed during the 1960’s.

Eutrophication of the Lake

Though still somewhat controversial (see Johnson et al. 2000), it is very likely that sedimentationand nutrient run-off, urban and industrial point source pollution and biomass burning, have indeed induced the rapid eutrophication of Lake Victoria over the latter part of the 20th century. Ambient conditions in Lake Victoria now favor thedominance of nitrogen fixingcyanobacteria and the spread aquatic weeds such as water hyacinth (Eichornia crassipes). Phosphorus levels have increased 2-3 times over the last 40-50 years (Hecky, 1993, 2000). Algal concentrations are three to five times higher now than during the 1960’s, and much of the lake bottom currently experiences periods of prolonged anoxia that were uncommon 40 years ago (Mugidde, 1993; Johnson et al., 2000).

 

Scheren (1995) suggests that the increase in phosphorus is primarily due to increases in atmospheric deposition from forest burning and wind erosion. On the other hand, Bullock et al., (1995) estimated that 50% of the nitrogen input and 56% of the phosphorous input is due to runoff from agricultural land, 30% of the nitrogen and 30% of the phosphorous is due to rural domestic waste, and 10-15% due to urban waste and atmospheric deposition. It should be noted that these figures are based on estimates and models rather than measurement of actual nutrient inputs from the various potential sources. Notably, both these estimates are based on models and ball-park estimates rather than measurements. There can be little progress in pinpointing the source of the problem until measurements of the various inputs are made.
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The Spread of Water Hyacinth

Water hyacinth (Eichhornia crasipes) began to colonize Lake Victoria around 1989, from the River Kagera which originates in Rwanda and passes through Tanzania and Uganda. Water hyacinth has covered as much as 680 square kilometres of the Lake, with enough new hyacinth carried into the lake to cover about 3 hectares per day. Water hyacinth is concentrated along the shorelines where it has most impact on people’s lives. Mats of water hyacinth cover about 80% of the Ugandan shoreline and 2000 hectares around the major Kenyan port at Kisumu (Ong’ang’a and Munyrwa, 1998; Pearce, 1998). New, vigorous hyacinth nurseries developing in the deltas of Rivers Siyu and Nzoia. (Robertson, pers. comm..). Potentially negative impacts on the Lake environment, include: (1) decomposition and sedimentation of rotting water hyacinth, (2) impeded light penetration leading to reduced growth of phytoplankton and herbivorous fish populations such as tilapia; (3) increased evapotranspiration and thus an increase in the rate of water loss; and (4) reduction in the diversity of aquatic plants and fish species (Ong’ang’a and Munyrwa, 1998).

Colonization by the water hyacinth has also had a number of direct economic impacts. While a full economic assessment of the economic impacts is not, to our knowledge, available at this time, a number of negative economic impacts have been noted. Commercial transportation has been slowed and made more costly and more risky.There has been a drastic decline in fish landings: a 50-75% reduction according to Ong’ang’a and Munyrwa (1998). Shoreline communities that were previously supported by fishing have been choked off. Many people in those communities have moved and those who remain have been forced to find alternative sources of livelihood. Bridges and dams have been damaged and the major power source for Uganda is under threat. At the Owen Falls hydroelectric plant on the Nile River in Uganda, four boats fitted with rakes and conveyer belts are needed to keep the turbines free of the weed. The cost of this operation alone is over $600,000 per year. Even with a clear surface, however, dead water hyacinth is dragged into the turbines by undercurrents. The turbines need to be shut down and cleaned each week, resulting in frequent power interruptions (Ong’ang’a and Munyrwa, 1998).

Losses of Biodiversity

Since Lake Victoria arose from a dry landscape 14,600 years ago, it has experienced rapid evolution of endemic species of cichlid fish, providing one of the most diverse flocks of fish species on Earth (Johnson et al. 2000). However, by the 1980s, some 400 endemic species were approaching extinction (Witte et al., 1992). The introduction of Nile Perch into Lake Victoria in early 1950 has been blamed for dramatic shifts in algal populations and the extinction of cichlids. However, the sedimentary record from well-dated short cores of the open lake, suggest that the lake system was poised for disaster since the early 1930s, parallel with the rise in human populations and agricultural activity (Johnson et al., 2000). Further evidence is required to confirm a cause-effect link between land degradation and loss of biodiversity in the lake.

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