National Agricultural Research Organisation (NARO), Fisheries Resources Research Institute (FIRRI),
P.O. Box 343, Jinja, Uganda. E-mail: firi@infocom.co.ug

Factors influencing proliferation of water hyacinth in Lake Victoria, Uganda

This study examined factors influencing proliferation of water hyacinth in Lake Victoria, Uganda. In less than 10 years since mid 1980s, more than 80% of Lake Victoria shoreline had been colonized by water hyacinth. Proliferation was associated with sheltered shallow (< 5m) bays and muddy lake bottom. Characteristic of these habitats were native macrophytes notably Cyperus papyrus in addition to ample SRP concentrations. This paper reports on data of SRP and its role in water hyacinth proliferation. Water samples were collected from 9 bays on a monthly basis for a year and analyzed for SRP and TP. SRP was positively correlated with weed biomass and growth vigour. Proliferation was remarkable at SRP concentrations above 10µg l-1. Murchison and Namirembe bays had average SRP concentrations above 400µg l-1 and 50µg l-1, respectively and were the major production centres for water hyacinth. Other bays were characterised as storage centres for water hyacinth because SRP concentrations were in most cases below 10µgl-1 and were characterised by arrested weed recruitment. With the rich Total Phosphorus (TP) reserves (>1000µg l-1 in Nakivubo Channel of Murchison Bay and >50µg l-1 in other bays) in surface sediments, the potential for proliferation of water hyacinth is high if these nutrient pools are biologically available for water hyacinth. However, management interventions through biological control have brought water hyacinth proliferation under control especially in storage bays (with <10µg l-1of SRP). In Murchison Bay, biological control has been established but its impact on water hyacinth growth and cover is minimal due to high concentrations of SRP that correlate strongly with luxuriant weed growth and recruitment.

Nutrients, notably SRP and probably NO3-N strongly influence proliferation of water hyacinth. Weed management should partly focus on the role of nutrients, their sources and how these can be reduced to mitigate enhanced proliferation.