Nutrient status and retention in pristine and disturbed wetlands in Uganda: management implications |
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Authors: | F Kansiime E Kateyo H Oryem-Origa P Mucunguzi |
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Institution: | (1) Institute of Environment and Natural Resources, Makerere University, P.O. Box 7062 Kampala, Uganda;(2) Department of Botany, Makerere University, P.O. Box 7062 Kampala, Uganda |
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Abstract: | Wetlands in Uganda experience different forms of human pressure ranging from drainage for agriculture and industrial development
to over harvesting of wetland products. In order to develop sustainable management tools for wetland ecosystems in Uganda
and the Lake Victoria Region, water quality analyses were carried out in a rural undisturbed (pristine) wetland (Nabugabo
wetland in Masaka) and two urban wetlands that are experiencing human and urban development pressure (the Nakivubo wetland
in Kampala and Kirinya wetland in Jinja). The former wetland forms the main inflow into Lake Nabugabo while the other two
border the northern shore of Lake Victoria, Uganda. Nabugabo wetland buffers Lake Nabugabo against surface runoff from the
catchment, while Nakivubo and Kirinya wetlands provides a water treatment function for wastewater from Kampala City and Jinja
town respectively, in addition to buffering Lake Victoria against surface runoff. Water quality was assessed in all the wetland
sites, and in addition nutrient content and storage was investigated in the main plant species (papyrus, Phragmites, Miscanthidium and cocoyam) in Nakivubo and Kirinya wetlands. A pilot experiment was also carried out to assess the wastewater treatment
potential of both the papyrus vegetation and an important agricultural crop Colocasia esculenta (cocoyam). Low electrical conductivity, ammonium–nitrogen and ortho-phosphate concentrations were recorded at the inflow
into Nabugabo wetland (41.5 μS/cm; 0.91 mg/l and 0.42 mg/l respectively) compared to the Nakivubo and Kirinya wetlands (335 μS/cm;
31.68 mg/l and 2.83 mg/l and 502 μS/cm; 10 mg/l and 1.87 mg/l respectively). The papyrus vegetation had higher biomass in
Nakivubo and Kirinya wetlands (6.7 kg DW m−2; 7.2 kg DW m−2 respectively), followed by Phragmites (6.5, 6.7), cocoyams (6.4, 6.6) and Miscanthidium (4.0, 4.2). The papyrus vegetation also exhibited a higher wastewater treatment potential than the agricultural crop (cocoyam)
during the pilot experiment (maximum removal degree of ammonium–nitrogen being 95% and 67% for papyrus and yams). It was concluded
that urbanisation pressure reduces natural wetland functioning either through the discharge of wastewater effluent or the
degradation of natural wetland vegetation. It is recommended that wetland vegetation be restored to enhance wetland ecosystem
functioning and for wetlands that are not yet under agricultural pressure, efforts should be made to halt any future encroachment. |
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Keywords: | Wetlands Nutrient retention Wetland degradation Wastewater treatment Management implications Sustainable development Uganda |
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