Abstract

The Lubigi wetland, which is located in the north-western part of Kampala, the capital city of Uganda has been severely strained from anthropogenic encroachment and activities. These activities include harvesting of Cyperus papyrus and other plants, land filling for reclamation, human settlements and disposal of wastewater into the wetland among others. As a result of these anthropogenic activities, the macrophytes diversity and biomass in the wetland have been affected, which in turn affects the effectiveness of wetland for removal of pollutants. It is therefore important to investigate the characteristics of wetland macrophytes in the Lubigi wetland. Pertinent field investigations, surveys, data collection and laboratory tests and analyses were carried out. The problem being addressed was the current lack of information and knowledge about the biomass and biodiversity of the Lubigi wetland to protect the downstream Mayanja River and Lake Kyoga. Three transects each of 1.0 m wide was cut across this zone at about 700 m downstream of the main wastewater inlet, the second at about 1,440 m downstream of the main wastewater inlet and the third at about 1,930 m downstream of the main wastewater inlet. In each of the 3 transects, 5 sampling points were established. Samples were analyzed in order to determine plant biomass, diversity, density and vegetation zonation. The determination of nitrogen content in the biomass parts and sediments was also carried out in accordance with standard methods for the examination of samples. The results show that there are 9 dominant native wetland plants species, which account for about 60% of all the plants species recorded. Of these dominant plant species, three exhibited the monotype form of dominance, one is ubiquitous, the other three were the compressed form of dominance, six are aberrant, two are diffuse and one is patchy. The most dominant species are C. papyrus, Echinochloa pyramidalis, Typha capensis, Rottboellia cochinchinensis and Oldenlandia lancifolia, with biomass production mean values of 1.52±0.13, 0.16±0.03, 0.26±0.04, 0.03±0.01 and 0.37±0.05 kgDWm^-2, respectively. However, there is no statistically significant difference between the biomass of the plant species in the three transects. Plant densities range from 5.0±3.09 to 19.56±15.29 plants/m², with a mean value of 10.19±4.69 plants/m². The overall mean plants and sediments nitrogen content are 67.54±37.9 and 157.5 g/m², respectively.

Key words: Lubigi wetland, plant biodiversity, plant biomass, plant density, vegetation zonation.