The effect of wastewater discharge on biomass production and nutrient content of Cyperus papyrus and Miscanthidium violaceum in the Nakivubo wetland, Kampala, Uganda

The nutrient content of representative plant parts and biomass production in the Nakivubo wetland, correlation of these with the wastewater flow patterns and determination of nutrient uptake, storage and biomass production of Cyperus papyrus (papyrus) and Miscanthidium violaceum was studied. On average papyrus vegetation under the influence of wastewater had higher nutrient content in the above ground biomass (1.6% N and 0.23% P on dry weight basis) than those not affected (0.98% N and 0.18% P). The biomass varied between 3,529-5,844 g/m² and 883-1,156 g/m² in the two respective sites. The juvenile plants of papyrus and Miscanthidium had higher concentrations of P and N in their organs compared to the mature ones. Considering the nutrients stored by the dominant vegetation and the current flow patterns of wastewater in the Nakivubo wetland, harvesting of the above ground biomass once a year, would remove 7.7% of the N input and 15.8% of the P input of the annual total load entering the wetland. However, if the wetland is bio-manipulated and the wastewater flow distributed over the whole wetland, up to 70% nitrogen and 76% phosphorus would be removed by harvesting above ground papyrus biomass.