Impact of immigrant pastoral herds to fringing wetlands of lake Victoria in Magu district Mwanza region, Tanzania

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Abstract

The assessment of impacts of pastoral herds to the fringing wetlands of Lake Victoria in Magu district in Mwanza region was carried out in 1999/2000. Lamadi village located along Speke Gulf of Lake Victoria was chosen. The main farming systems in the area are agriculture, agro-pastoralism, and pastoralism. The wetlands are heavily used for livestock grazing during the dry season. Since 1990s the area has been experiencing a high influx of immigrant pastoral herds from drought prone districts. The increasing livestock numbers have led into serious degradation of wetlands. The type of damages includes: soil erosion, loss of vegetation cover and deforestation. This lead to pollution of Lake Victoria along the Speke gulf in particular as the wetlands was buffering a lot of pollutants from the catchments. The range condition at Lamadi was rated fair. The carrying capacity of rangelands was estimated at 3.57–6.75 ha/LU and the wetlands were seriously degraded causing heavy soil erosion and environmental pollution during rainy season. It was recommended to raise people’s awareness on conservation of environment and mobilise communities to take responsibility on management of the environmental resources.

Introduction

Studies on the annual cycles of stratification and phytoplankton growth in Lake Victoria, by Talling in 1966, studies on nutrient dynamics and turnover rates of phosphates and sulphates in Lake Victoria by Lehman and Branstrator (1994) and those studies of the role of climate in the modern condition of Lake Victoria by Lehman (1998) showed that the Lake Victoria was continuously being polluted. Historical data from Bugaya Islands in Uganda by Talling and Lehman showed that there was a decline in dissolved oxygen in the first 60 m depth of the lake. For instance Bugaya in 1961 January, had 4 mg/l of dissolved oxygen but by January 2001 the same area had only 2 mg/l of dissolved oxygen. They also showed that in May 1961 the area had 5 μg/l of phosphates but by May 2001 the area had about 100 μg/l of phosphates and the same area in August 1961 had 10 μg/l of nitrates/nitrogen but by August 1998 the area had 110 μg/l of nitrates/nitrogen. The increase of these chemicals especially the phosphates and nitrates were showed to be caused by human activities in the catchment especially agriculture and overgrazing in fringing wetlands of the Lake Victoria. This happened not only in Bugaya area alone but also in many places in the Lake Victoria basin including those on Tanzanian part. Degradation of fringing wetlands in the lake basin resulted into pollution of the lake as more pollutants were easily entering the lake from the catchment.

Wetland is a term used for large variety of ecosystems which have one thing in common; the presence of both land and water for most part of the year. According to the RAMSAR (2000) definition; “Wetlands are areas of marsh, fen, peat land or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh brackish or salt, including areas of marine water the depth of which at low tide does not exceed six meters”.

In Tanzania almost 10% of the country’s surface area is covered by wetlands (NEMC/WWF/IUCN, 1990). Wetland ecosystems are complex and processes within them were poorly understood for a long time until very recently. Wetlands have been recognised as playing an important role in buffering inputs from the basin catchments. Aquatic macrophytes in wetlands lower water velocities and act as filters leading to deposition of suspended sediments. Wetlands are among the most productive life support systems in the world and are of immense socio-economic and ecological importance to mankind.

Research and surveys have provided empirical evidence to show that wetlands are the most productive ecosystems of Tanzania (Loma, 1979; LRDC and ODA, 1987; Bwathondi and Ngoile, 1990; Mwalyosi, 1990; Semesi, 1990). These fabulous natural resources are continually being depleted and only rarely are sustainably utilized.

Wetlands around Lake Victoria like others play important roles to the lake ecosystem. They include high biodiversity, i.e. species of flora and fauna; buffer the lake from various pollutants, used for crop and livestock production. Despite these benefits, wetland resources in the Lake Victoria basin especially those in Magu district are continuously being overexploited making them unsustainable. Poor agronomic practices, overgrazing, wildfire, cutting of macrophytes for fuel, housing and commercial activities, illegal and improper fishing practices, agro-chemicals and introduction, illegally or otherwise, of non-traditional or alien species into wetlands (e.g. water hyacinth) are some of threats to wetlands surrounding the area.

With rising in human population, pollution (from catchment) has undoubtedly risen. Livestock production in the area constitutes an important component in livelihood support systems in the agro-pastoral farming system predominant in the semi-arid areas of Mwanza. Farming communities in this area are mainly sedentary operating subsistence mixed economies combining livestock and crop production.

Livestock in this area serves as: main source of income, source of draught power and manure, provide household food security and other social functions. The area is also highly populated by both human and livestock, also supports high populations of grazing wild game in Serengeti National Park Plains. The increasing human as well as animal populations and precarious climatic conditions are exerting immense, pressure on environment resources, leading to varying levels of land degradations such as soil erosion due to both over grazing and deforestation.

The livestock sector, in particular, gets severely affected during dry seasons. Large herds of cattle and wild game get concentrated in limited numbers of dry season grazing areas, like the wetlands around the Speke gulf of Lake Victoria basin in Magu district.

This has led to varying levels of over exploitations of wetland resources and there is now increasing conflicts over resource by multiple users of otherwise fragile ecosystem. As such livestock production in this area poses a great threat to fringing wetlands because overgrazing has been spotted as the major cause of increased soil erosion around these fringing wetlands. It was on this basis the LVEMP decided to carry out a study on the impacts of immigrant pastoral herds to fringing wetlands of Speke gulf of Lake Victoria in Magu district.

Although there are several fringing wetlands around Lake Victoria, Rubana fringing wetland which covers many villages in Magu and Bunda districts, Lamadi village in Magu district was chosen as study area due to the fact that has both high population of livestock and numbers of livestock coming from neighbouring districts (the immigrant livestock).

The general objective of the study was to investigate the impacts of immigrant pastoral herds on the fringing wetlands of the Speke gulf of Lake Victoria in Magu district.

Specific objectives:

  • To determine forage yield.

  • To determine range condition.

  • To determine socio-economic aspects of animal husbandry.

  • To determine the extent of damage caused by the pastoral herds in fringing wetlands of Speke gulf.

Section snippets

Methodology

Ecological as well as socio-economic surveys were conducted at Lamadi village and its sub-villages in Magu district in order to obtain baseline data. Both secondary and primary data were collected from the study areas. Secondary data were collected from publications, reports and information from various people. Primary data were collected through quantitative ecological and socio-economic surveys. A field survey was conducted at the site during August/September 1999 (the dry season). The survey

Results

Results for percentage cover, dry matter yield, density of woody species (trees per ha), range condition and carrying capacity (ha/LU) are outlined in Table 2. Plant cover for all the sub-villages at Lamadi, was below 50% but well above 25%. This means that their rating score was fair. Forage yield at Lamadi was highest at sub-villages of Mwabasabi A and B with 1320 kg/ha while the lowest figure was scored at Kalago with only 680 kg/ha. Mwabayanda and Mwabasabi B had the least tree densities by

Discussion

Findings during range surveys and socio-economic field studies gave indications of increasing environmental degradations of the wetland resources in the area. The extent f degradations were dependent on human and animal population, type of farming system, social economic activities of stakeholders, as well as ecological factors. Measures aimed at reversing such degradation processes should take into consideration the needs of stakeholders and livelihood support systems. The wetland around the

Conclusion and recommendations

The existing pastoral/agro-pastoral system of keeping livestock has aggravated a number of problems pertaining to land resources. It was concluded that overgrazing had adversely resulted into loss of forage yield, vegetation and leaving a lot of bare ground, and bush encroachment. Other impacts include poor range condition, encroachment of undesirable forage species, including poisonous plants i.e. Sporobolus, Linchelitrum, Aristida, Lantana camara and Solanum incanum; siltation and

Acknowledgements

The authors would like to thank LVEMP for funding the research, National Environment Management Council for Coordinating the study and also the Livestock Training Institute (LITI), Morogoro for their collaboration and wetland management component staffs for their high cooperation during the studies. Finally authors would like to acknowledge the reviewers of this.

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