Competitive interaction between Eichhornia crassipes and Pistia stratiotes at two different nutrient levels and the socioeconomic importance of Eichhornia crassipes in the Winam Gulf, Lake Victoria, Kenya
Onwong'a, R. (2012). Competitive interaction between Eichhornia crassipes and Pistia stratiotes at two different nutrient levels and the socioeconomic importance of Eichhornia crassipes in the Winam Gulf, Lake Victoria, Kenya.. MSc Thesis. VUB: Brussel. 76 pp.
The impacts of invasive alien species (IAS) on the ecosystems, health and economies may prevent developing countries from achieving their Millennium Development Goals. Various methods have been put into place to control these IAS because eradication is not easy once the species has established itself. Water hyacinth Eichhornia crassipes is the most problematic invasive alien macrophyte found in Lake Victoria. We sought to investigate whether nutrient reduction and water hyacinth utilization could have an effect on the growth of water hyacinth. Specifically, we sought to compare the performance of Eichhornia crassipes and Pistia stratiotes in mesotrophic and eutrophic conditions. We further sought to understand the mechanisms of interactions and population dynamics between E. crassipes and P. stratiotes. Growth experiments of the two species were conducted in outdoor tanks at the Winam Gulf, Kenya and competition experiments were conducted at the Vrije Universiteit Brussel greenhouse. For competition experiments, a complete additive design with factorial combinations of the two species was followed. Hoagland solution with modified P was used to supply the nutrients. Using a questionnaire that had closed and open-ended questions, water hyacinth utilization, impacts of water hyacinth to the local communities and the communities’ perceptions towards the macrophyte was assessed. Our results showed that nutrient reduction negatively affected the performance of both species. However, dry biomass accumulated by E. crassipes was not affected by nutrient treatment and at the end of the experiments, there was no significant difference in dry biomass in all-planting densities between the two nutrient levels. Overall, P. stratiotes had a higher RGR than E. crassipes in all planting densities and in both nutrient conditions. At the end of the experiment, standing composition shifted towards P. stratiotes. The socio-economic survey indicated that water hyacinth utilization did not control the dense mats of the macrophyte and despite the negative impacts of water hyacinth; majority of the respondents did not want the macrophyte eliminated. From our study, it was evident that nutrient reduction and water hyacinth utilization cannot control the dense mats of water hyacinth. Therefore, these two can only compliment other methods of water hyacinth control.
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