Title: Assessment of the impact of flower farming on wetland ecosystems and ecosystems services: a case study of Lutembe Bay wetland, Uganda
Author: David Were
Supervising Institution: IHE Delft - Institute for Water Education
Wetland ecosystems support livelihoods through provision of economic, social, environmental and cultural benefits. They can provide all these benefits simultaneously if they are sustainably exploited. However, most current wetland exploitation decisions are being based more on a response to economic and political pressures than on the sustainable benefits obtained from these ecosystems. As a result, some benefits are prioritized over others. The aims of this study were 1) to assess the impact of expansion of flower farming on wetland hydrology and vegetation, 2) to assess the impact of expansion of flower farming on selected provisioning, cultural and regulating ecosystem services, and 3) to develop and apply a checklist for assessing the impact of the prioritized ecosystem service on other ecosystem services, vegetation and hydrology. The study was done in Lutembe Bay wetland ecosystem in Uganda, where flower farming had been the prioritized ecosystem service. It focussed on comparing the condition of hydrology, vegetation and ecosystem services before and after expansion of flower farming into the wetland. To assess the impact of expansion of flower farming on wetland water quality, water sampling was done in three streams which discharged into the wetland. Two streams were effluent streams originating from two flower farms, while the third stream did not originate from a flower farm. Nitrogen (NH4-N, NO3-N and TN) and phosphorus (SRP and TP) concentrations were measured. Concentrations of the same forms of nitrogen and phosphorus were also measured in the Bay and compared to those measured before expansion of flower farming. Semistructured interviews were used to assess the impact of expansion of flower farming on wetland water levels, vegetation, and ecosystem services. To develop and apply the checklist for assessing the impact of the prioritized ecosystem service on other ecosystem services, vegetation and hydrology, I selected indicators of the condition of ecosystems services, vegetation and hydrology. Using the interview data obtained from objectives 1 and 2, I created a table which reflected the trends and magnitudes of change of these indicators, and which also gave a link between the trends of these indicators to the prioritized ecosystem service. The results showed that nutrient concentrations in effluent streams from flower farms were not significantly different from those in the stream which did not originate from a flower farm (p>0.05), except for SRP and TP in effluent stream from one flower farm which were significantly higher (p<0.05). There was also no significant difference in nutrient concentrations measured in the Bay before and after expansion of flower farming (p>0.05), except for TP, which was significantly higher (p<0.05). Most respondents showed that surface water levels and water flow alterations in the wetland had increased. They also observed that vegetation health and percentage cover of the dominant species had decreased, while species composition and incidence of invasive species had not changed. Provisioning services of fishing, crop cultivation, papyrus harvesting, clay mining and water abstraction had decreased, while sand mining had increased. Cultural services of ecotourism and education had increased, while spiritual value had decreased. Regulating services of flood and soil erosion regulation had not changed, while water purification had decreased. The developed checklist showed that most respondents linked the decrease in fishing, crop cultivation, clay mining, water abstraction, spiritual value, water purification, vegetation health and percentage cover of dominant vegetation species, and the increase in water flow alterations, ecotourism and education values to expansion of flower farming. The checklist further showed that most respondents recognized that their magnitudes of change had been big, except for vegetation health (which had decreased by a small magnitude). In conclusion, the study indicates that expansion of flower farming has not significantly impacted on nutrient concentration in the wetland, except SRP and TP, while it has increased water flow alterations by a big magnitude. It has also decreased vegetation health, but by a small magnitude, while percentage cover of dominant vegetation has been decreased by a big magnitude. It has also decreased provisioning services of fishing, crop cultivation, water abstraction and clay mining by a big magnitude. Cultural ecosystem services of ecotourism and education have been increased by a big magnitude, while spiritual value has been decreased by a big magnitude. Water quality regulation has also been decreased by a big magnitude. The developed checklist gives a clear picture of how wetland users relate the trends of the condition of ecosystem services, vegetation and hydrology to the prioritized ecosystem services, in a summarized way. It was recommended that more studies should be done especially looking at the possible impacts of pesticides used by these flowers farms on vegetation, bees, fish, and human health.
Key words: wetland, ecosystem, ecosystem services, expansion, flower farming