Mabamba-Mpanga

A(i)Site contains one or more globally threatened species, C(iii)Site contains nationally threatened or restricted habitat or vegetation types, AND/OR habitats that have severely declined in extent nationally

Mabamba-Mpanga qualifies as an IPA under criterion A(i) as one of the only sites nationally for the globally Endangered species Aldrovanda vesiculosa and an important site nationally for the globally Vulnerable Cnestis mildbraedii and Entandrophragma utile. Moreover, it qualifies under C(iii) as one of the best sites for nationally Vulnerable habitat freshwater marshes. This ecosystem provides numerous valuable ecosystem services and sustainable usage will protect the livelihoods associated with this site in the long-term.

The Mabamba-Mpanga IPA is located across Mpigi and Wakiso Districts of the Central Region of Uganda where the Katonga River reaches Lake Victoria. The IPA is based largely upon the Mabamba Bay Wetland System Ramsar site, a permanent marsh located on the edge of Lake Victoria, 20 km southwest of Kampala and 10 km west of Entebbe. However, the boundary of the site is modified somewhat from the Ramsar boundary to more accurately reflect the intact wetland system, and the north of the IPA incorporates Mpanga Central Forest Reserve, a small area of intact moist forest lying outside the Ramsar site. The IPA is crossed in the north by the main Kampala-Masaka road near to Mpigi town.

The Mabamba Bay Wetland System is an important example of the nationally Vulnerable habitat, freshwater marsh. According to the Ministry of Water and Environment, wetlands are under significant pressure nationally and are estimated to have declined from 17.5% national coverage in the 1990s to 8.5% by 2021 (Wambede, 2021). Other wetlands, such as the Mpologoma freshwater marsh near Lake Kyoga, have been degraded due to land shortages and resulting agricultural encroachment, particularly rice farming (Bunyangha et al. 2022). Increased flooding in the Mpologoma area has been linked to this agricultural encroachment (Wambede, 2021). Conservation of the freshwater marsh within Mabamba Bay is, therefore, of great importance in order to avoid the loss of flood mitigation and many other crucial ecosystem services provided by wetland habitats (see Key ecosystem services).

There is also one globally threatened species known from the Ramsar site, the waterwheel (Aldrovanda vesiculosa) which is assessed as Endangered. While this carnivorous aquatic species is wide ranging, native to parts of Africa, Asia, Australia and Asia, it is threatened by expansion of agriculture, pollution and hydrological changes, including freshwater drainage (Cross & Adamec, 2020). Aldrovanda vesiculosa is also threatened nationally by swamp reclamation for agriculture and was therefore assessed as nationally Endangered due to a decline in its range (Kalema et al. 2016). Mabamba Bay is one of only three sites in Uganda from which this species is known and is therefore crucial to its conservation nationally. Furthermore, although not threatened or range restricted, Leersia friesii, a very uncommon grass species in Uganda, is only known from Mabamba Bay and around two satellite lakes near Nabugabo and is locally rare in all three localities (Kalema, 2005).

Mpanga Central Forest Reserve (CFR) is a small (453 ha) but important area of intact Medium Altitude Moist Forest, with over 200 tree and shrub species documented to date (Lwanga 1996), including three threatened tree species, namely Cnestis mildbraedii (VU), Entandrophragma cylindricum (VU) and E. utile (VU).

The Mabamba Bay Wetland System is dominated by the grass Miscanthus violaceus (Miscanthidium violaceum), while the edges are largely composed of Cyperus papyrus (Byaruhanga & Kigoolo, 2005). In narrow channels of open water, species such as the waterlily Nymphaea nouchali var. caerulea and the sedge Cladium mariscus are frequent (Ministry of Water and Environment, 2015).

The edges of this wetland would previously have had areas of Piptadeniastrum-Albizia-Celtis forest, as noted in several areas by Langdale-Brown et al. (1964). However, very little of this forest remains and the many, small forest reserves and non-protected forests situated at the fringes of the wetlands appear to now encompass Eucalyptus plantations (Google Earth, 2023; Jones, 2021). A significant exception is the Mpanga CFR which still holds intact moist medium altitude mixed forest with Albizia, Antiaris, Celtis, Entandrophragma and Lovoa amongst the dominant elements (Taylor et al. 2008). Although mapped as Medium Altitude Evergreen Forest, several semi-deciduous forest indicators are present, such as Celtis spp. (Lwanga 1996).

The Mabamba Bay Wetland System was designated as a Ramsar site in 2006 and so is accorded legal protection as a conservation area. The site was also recognised as an Important Bird Area (Byaruhanga et al. 2001), due to the important habitat it provides for birds such as the Vulnerable species Shoebill (Balaeniceps rex), and falls within the Katonga River Mouth Key Biodiversity Area, which is triggered by the presence of Ningu (Labeo victorianus) a species of fish endemic to the Lake Victoria Basin (Plumptre et al. 2017).

Despite its importance for both species and ecosystem services, Mabamba Bay faces numerous threats. Several of these are caused by disturbances in the catchment area and wetland shores. Wetland edge agriculture and horticulture, for instance, may be introducing agrochemicals into the waters, changing nutrient levels and ecological dynamics (Byaruhanga & Kigoolo, 2005). Loss and degradation of forest and bush burning may also lead to disruption of water dynamics in the catchment area, soil erosion and siltation of waterways and wetland areas (Zake, 2014). However, this wetland is known to play a role in water filtration, preventing and so there may be some tolerance of increased siltation (Byaruhanga & Kigoolo, 2005; Zake, 2014). The establishment of Eucalyptus plantations at the edge of the wetlands may well also impact the resilience of this ecosystem. There is evidence that Eucalyptus monocultures have lower bird diversity compared to other habitats around Mabamba Bay, however, it is not known whether planting of these trees also impacts the wider ecosystem, for instance, through altering water dynamics (Jones, 2021).

Alongside disturbances adjacent to Mabamba Bay, several threats are occurring within wetland areas. The invasive water hyacinth, Eichhornia crassipes, is present within this IPA. This species is known to outcompete other macrophytes (Lake Victoria Basin Commission, 2011) and could impact populations of Endangered Aldrovanda vesiculosa at this site.

Furthermore, prolonged drought periods are causing crops to fail and forcing people to encroach into wetland areas to extract resources (Zake, 2014). Livestock are kept in the wetlands during the dry season, while there has been increased papyrus extraction which is increasingly being used as a source of fuel alongside longstanding uses for fibres and crafts (Byaruhanga & Kigoolo, 2005; Zake, 2014). In addition, illegal sand mining threatens parts of the wetlands. Vegetation mats are cleared to access the substrate and the extracted sand is subsequently used in the construction industry (Nile Basin Initiative, 2022). Alongside threatening the ecosystem, this practice may threaten public health as the sand pits left fill with water and become breeding grounds for mosquitos (Akwetaireho & Getzner, 2010). Further research is needed to better understand how this ecosystem can be used sustainably to support livelihoods in the long term and to what extent ecosystem modifications impact the provision of ecosystem services.

In order to increase the sustainability of local livelihoods, the Lake Victoria Environmental Management Project was initiated between the governments of Kenya, Tanzania and Uganda in the late 1990s. The aims of the project include monitoring water quality, control of invasive water hyacinth and managing fisheries and use of land and wetlands (World Bank, 1996). There have since been three phases of this project, including work with stakeholders at Mabamba Bay on sustainable livelihoods (Akwetaireho & Getzner, 2010; World Bank, 2020). Environment Alert, Nature Uganda, Nature Palace and the Ecological Christian Organization in partnership with Pathfinder International have all been involved in biodiversity conservation initiatives in the area, including promoting sustainable livelihoods, upholding the site’s Ramsar status and raising awareness of conservation issues (Zake, 2014).

Mpanga CFR was established in 1932 and was designated in 1951 as a Research Forest Reserve, with the aim to research the productivity of indigenous forest trees. As such, a permanent 80 x 80 m permanent research plot was established there in 1968 and has been subject to long-term survey (Taylor et al. 2008). The forest suffered from pit-sawing of timber trees prior to the 1950s but showed significant regeneration up to the 1990s. Since that time, increasing demand for timber for wood-carving and construction, heightened by proximity to the Kampala-Masaka road, has led to increased illegal logging within Mpanga (Taylor et al. 2008).

Mabamba Bay is a key area for ecosystem service provision. The area is a critical breeding ground and nursery for fish that later migrate into Lake Victoria. Lake Victoria accounts for 58% of Uganda’s fish catch while the fishing activities at the five landing sites operated within the Mabamba Bay area were valued at 561,088 USD in 2008 (Akwetaireho & Getzner, 2010). Arable farming on the fridges of Mabamba Bay relies upon water supply from the wetlands and is also supplemented by nutrients from the marsh. Livestock farmers also depend on pasture, fodder and water collected from the site and, in the dry season, fishing communities keep livestock in the wetlands (Byaruhanga & Kigoolo, 2005). The site also provides a source of drinking water for people, fuelwood and materials. Papyrus is particularly important and is used as material in crafts and, more recently, has been harvested as a fuel source, possibly due to a scarcity of fuelwood (Byaruhanga & Kigoolo, 2005; Zake, 2014). Sand mining takes place at this site, although this activity is prohibited (see Conservation issues). It was estimated by Akwetaireho & Getzner (2010) that the wetland provides an annual 130 USD per capita for the local community through ecosystem services (Akwetaireho & Getzner, 2010).

Mabamba Bay is of cultural significance to the Mamba (lungfish) clan of Buganda Kingdom (Lake Victoria Basin Commission, 2011). There is also tourism in the area, aided by the site’s proximity to Kampala, particularly birdwatching to see the iconic and threatened Shoebill (Balaeniceps rex). Ecotourism, including forest trails, is also established at Mpanga Forest.

The IPA is important for carbon storage and, although there are no estimates yet for the volume of carbon stored within these wetlands, the site has peat soils which are known to be highly effective carbon stores (Elshehawi et al. 2019). The wetland vegetation is also important for filtering sediments from the water before it enters Lake Victoria and stabilising soils (Nile Basin Initiative, 2022). The ecosystem is likely also important in moderation of extreme events, particularly flooding.

Assessed by:

Sophie Richards, Royal Botanic Gardens, Kew

Iain Darbyshire, Royal Botanic Gardens, Kew

Samuel Ojelel, Makerere University Herbarium

James Kalema, Makerere University Herbarium

Date of first assessment: 4th Nov 2024

Reviewed by:

Micheal Kibuule, Nature Uganda