Degradation of the riparian wetlands in the Lake Victoria basin - Yala swamp case study Thuita Thenya1, Reiner Wassmann2,3, Louis Verchot3, David Mungai1 1Department of Geography & Environmental studies, University of Nairobi, P. O. Box 30197-00100, Nairobi, Kenya 2Centre for Development Research (ZEF), University of Bonn, Walter Flex Str. 3, D-53113, Germany cWorld Agroforestry centre (ICRAF), P. O. Box 30677-00100, Nairobi, Kenya 3Institute for Meteorology and Climate Research, Kreuzeckbahnstraße, 19, D-82467 Garmisch- Partenkirchen, Germany Email :[email protected] According to Lal and Stewart (1985), soil Abstract degradation undermines the productive capacity of the ecosystem resulting for example in alteration of Land degradation is as a result of broad range of scales water status. Vegetation cover especially riverine and factors, which include biophysical, climatic, demographic and socio-economic. The aim of this paper vegetation act as natural filter of sediments was to provide an analysis of wetland utilisation, minimising silt deposition in water bodies. It is for ecosystem degradation and their effect on the Lake this reason that wetlands are valued for their Victoria ecosystem. This involved analysis of socio- ecological services like shoreline protection (Daily, economic and remote sensed data. The main sources of 1997) and support to biodiversity among others wetland degradation in the Lake Victoria basin were (Barbier, 1993). In many countries especially in the identified as (i) farming activities, (ii) grazing and developing world, local economies depend on macrophyte harvesting and (iii) coupled with catchment wetland utilization such as reed harvesting, grazing, degradation-deforestation. These factors were closely and farming especially in the dry regions (Adelaida, related to the demographic dynamics and unsustainable land utilisation practices. Socio-economic data provided 2000). These activities often lead to change in valuable insight on the pattern of wetland utilisation and wetland vegetation cover. possible sources of degradation pressure. For example, there is high dependence of the local indigenous livelihood The increasing widespread lack of sustainable use directly on the swamp for subsistence needs including of wetlands especially in the developing countries farming, grazing and income generation. Farming is the can be attributed to the lack of recognition of the most important wetland utilisation activity, which takes traditional values of these wetlands, desire for 95% of the households wetland land holding mainly for modernisation (Panayotou, 1994; Maclean et al., subsistence use. In addition, there has been progressive 2003) and failure of appreciation of ecological role. degradation of the catchment area through deforestation, overgrazing and low furrow period. This results in high The most important sources of wetland degradation sediments transport and other pollutants to the lake emanate from the drainage for agriculture, ecosystem due to the removal of buffering effect of the settlement and excessive exploitation by the local macrophytes in the swamp especially along river Nzoia people. In addition, poor ecosystem management systems. Remote sensing data indicated progressive under increasing population generate high opening of the swamp especially in the high population degradation pressure. Quite often there are and more accessible northern side of the swamp. In numerous underlying factors to wetland degradation conclusion, the unsustainable use of natural resources in such as population increase (Ruthenberg, 1976; the basin has had significant negative effect on the Binswanger and McIntire, 1987; Pingali et al., 1987). Lake ecosystem including water pollution siltation and Other factors include international agreements, such increase of floating biomass. as IMF, World Bank trade liberalization and related national policies that affects farmers’ decisions on Key words: Degradation, macrophyte, remote sensing, land use. Extreme weather events like drought and utilisation, wetland, floods are also important (Turner et al., 1989). However, recent studies in East Africa on land use Introduction change have pointed out agriculture is the main cause of wetland degradation (Thenya, 2001; Land degradation is a process which implies a Mugisha, 2002; Torrion, 2002; Githaiga et al., 2003; reduction of potential productivity of the land (Hill et Reid et al., 2004). However, wetland conversion to al., 1995b). It is also considered to be a collective farming and settlements is not a new phenomenon. degradation of different components of the land such It is estimated that more than half of the wetlands in as water, biotic and soil resources (Hennemann, the world may have disappeared since the start of 2001). In broader sense land degradation is the the 20th century, with most losses being in the alteration of all aspects of the biophysical developed countries (Barbier, 1993). However, environment by human actions to the detriment of wetland loss is on the rise in the developing vegetation, soils, landforms, water and ecosystems. countries as a result of conversions mainly for 483 agricultural lands and urban settlements (Maltby, use changes and destruction of soil cover. Lake 1986; Farber and Constanza, 1987; Maltby, 1988; ecosystems are often downstream ecosystems that Mohamed, 1998; Torrion, 2002). Nonetheless are affected by changes both in the catchment areas dramatic losses have occurred over short space of and fringing wetland areas. The latter are supposed time (Maltby, 1988). to act as buffer to sediments and pollutants transport to the lake ecosystem. Studies on the adverse The main objective of this paper was to provide a effects of cattle grazing in forests in the catchments synthesis of wetland utilisation, ecosystem areas of Rivers Yala and Nzoia have shown the degradation and the effect on Lake Victoria aquatic infiltration capacity has greatly reduced in hardwood ecosystem using the Yala swamp, a large swamp and softwood forests from 190 to 1.3 and 280 to 33 area located on the north-eastern edge of Lake mm/hour respectively (JICA 1980 and 1991). The Victoria, Kenya. presence of forests and soil cover reduces the likelihood of serious soil erosion as the root system Ecosystem degradation and impact on aquatic physically binds the soil while the canopy and ecosystem ground litter physically protect the top soil by intercepting potentially destructive heavy rainfall and The wetland degradation forces are mainly a reduce the resulting runoff. Interception by the combination of the demographic factors like overhead canopy spreads the flow of water to the population density, settlement, food deficit and ground over longer period of time and allows more institutional support failure (Hollis, 1990). Some of time for infiltration into the soil, which recharges these wetland changes are within planned ground water. The effect of extensive destruction of development scheme, like draining for rice farming the soil cover including forest and reduced fallow on the upper part of the Senegal River (Halls, 1997; period hamper infiltration and encourage high rivers Drijver and Van Wetten, 2000). However, others are discharge. There has been a general increase in as a result of uncoordinated – and often illegal – river flow discharge over the years as well as an activities of the local people (Panayotou, 1994). increase in rainfall run-off possibly resulting from the Demographic changes coupled with poor degradation of the catchment. The average river environmental policy have in various cases discharge both in the Yala and Nzoia rivers have aggravated the degradation of the wetland increased over the years, for example their resources. For example, unsustainable wetland discharge in the period 1990-2000 was higher than utilization in Ethiopia has been attributed to the for the period 1950/60 (Sangale et al., 2001). combined changes in policy, political regimes and demographic dynamics (Thompson, 1976; Wood, The different sub-catchment in the lake basin 1997; Wood et al., 1998). contributes varying amounts of sediments to the Lake Victoria depending on the local settings. For The Lake Victoria basin (LVB) faces far more example, although the total land cover under complex social, economic, political and technical cultivation in the basin in Kenya and Tanzania is barriers than other transboundary lakes in the region comparatively smaller, the two countries contribute (Duda, 2002). The environmental degradation of LVB relatively higher sediments to the Lake Victoria over the last 3 decades, due to unsustainable use of (Table 1). This is due to their close location of the natural resources has had significant effect on the catchment relative to Lake Victoria and the step Lake ecosystem. These include massive algal topography (Table 1). In contrast, Uganda has blooms, waterborne diseases, water hyacinth smaller sediments contribution through the river infestation and oxygen depletion (Odada et al., system since it is at the out flowing direction. 2004). Changes in land-use pattern have lead However, in spite of the distant location of the fundamentally to spatial and temporal heterogeneity Rwanda and Burundi catchments, the high of the limnological characteristics thus influencing percentage of land under cultivation contributes ecological structure and functioning of the aquatic relatively high percentage of sediments and other ecosystems (Nogueira et al., 1999). Accurate pollutants into the lake