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Nakivubo Wetland, Uganda
Many wetland ecosystems in Uganda are under threat of being lost primarily as a result of infilling or drainage to create land for agricultural use or urban development. These wetlands perform important socio-economic and ecological functions such as maintenance of surface and groundwater supplies, water purification, flood control, edge cultivation and habitat functions. In rural and urban areas, many Ugandan people are engaged in wetland farming, papyrus harvesting, pottery, brick making and sand mining. In urban areas wetlands purify industrial, commercial and domestic effluents like sewage and dirt washed down with rainstorms through urban centre drainage systems.Nakivubo wetland, a proposed case study is an urban wetland located in Kampala Uganda.




Geographic location:
  • Located between latitudes 00° 17' and 00° 19' N and longitudes 32°37' and 32°39' E, at an altitude of 1135 m above sea level, Nakivubo wetland lies about 5 km south-east of Uganda's capital city, Kampala (Figure 1). It separates the city with the Inner Murchison Bay and Lake Victoria. The 5.29 km2 swamp drains a total catchment area of about 50 km2 from the rapidly growing affluent Kampala City.
  •  Nakivubo wetland is bisected by a railway line running through Central Kampala to Port Bell on Lake Victoria (Figure 2). While areas to the north of the railway have been substantially modified, to the south the wetland is relatively intact. Much of the shallow upper part of the wetland has been reclaimed for settlement and industrial development, or is under cultivation. Deeper parts of the wetland between the railway line and Murchison Bay comprise a floating papyrus swamp, and contain only small amounts of cultivation on their fringes. Unconverted parts of Nakivubo wetland are dominated by papyrus (Cyperus papyrus) grading to dry land through cattails (Typha sp.) and common reeds (Phragmites sp.), with a large area on the north east side covered by Miscanthidium grass.



Ecosystem services current status

Wastewater Treatment by the Nakivubo Wetland

According to Emerton et al. (1999), the highest economic value (90% of the total value) that Nakivubo wetland provides as a service is that of wastewater treatment whereas agriculture dominated resource utilisation value in the wetland. Recent research (Kansiime and Nalubega, 1999) showed that the Nakivubo wetland performs considerable tertiary treatment of the effluents it receives from the sewage works and Kampala. As such the wetland protects the Inner Murchison Bay from eutrophication and excessive loads of pathogens which otherwise may be transported to the nearby Gaba waterworks, posing a threat to public health.

Farming in the Nakivubo Wetland
There are several farming activities in and around the wetland. Coco yam growing accounts for 70 - 80% of the agricultural activities in the wetland. Other cultivated crops include cassava, potatoes and sugarcanes and these are grown at the edges or where the wetland has been completely drained (e.g. in Kitintale). In the past (pre-1991), the farming used to be localised on the upper part of the wetland, but it is currently proceeding towards Inner Murchison Bay at an alarming rate. The only restriction to extensive wetland reclamation is the water in the lower wetland, which becomes deeper towards the Inner Murchison Bay.

Papyrus Versus Coco yams in Wastewater Treatment
There has been a standing question as to which of the plants (Coco yam and papyrus) is a better candidate for wastewater treatment. From the research carried out carried in Nakivubo wetland and other wetlands around Lake Victoria, papyrus seem to be a better option for wastewater treatment.
Papyrus is characterised by a loose mat (a compartment where floating aquatic plants are anchored) and strong rhizomes (Azza, 1996; Kipkemboi, 1999; Azza et al, 2000) and has one of the highest biomass productivity reported for wetland plants (Howard-Williams and Gaudet, 1985). The loose mat allows the wastewater to easily interact with the plant roots. During this interaction plants take up nutrients and other processes like attachment and sedimentation are enhanced. The latter two processes are important for the retention of pathogens and suspended solids.
Yams are grown in mounds, which do not hold the solids particle together. These results flushing out of suspended matter and loose sediment as the water flows through the wetland. This situation becomes worse during the storm events whereby some yam plants are carried with storm water downstream. This implies the plants are not firmly held in the soil.

Biomass Harvesting
Papyrus harvesting is dominant activity in the wetland and is currently concentrated in the lower wetland. Papyrus plants are harvested by local people and sold for craft making, thatching houses and making fences. The practice of cutting and clearing wetland vegetation for domestic use is widespread and has been on the increase since imported building materials are expensive. Iron sheets for roofing houses, for example, has often been replaced by papyrus thatching especially for the low-income earners. In addition to the income obtained from selling papyrus products, harvesting removes nutrients from the wetland. Up to 50% (annual nitrogen load entering the Nakivubo wetland can be maximally removed from the wetland through papyrus harvesting.
 
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The project is funded by and is part of
WLE Nile and East Africa
Regional programme.