Effects of hydrological changes on water quality and cyanotoxins in Nyanza Gulf, L.Victoria,Kenya

Session: Harmful Algal Blooms: From Ecosystem Drivers to Ecosystem Impacts (2)

Benard Mucholwa, The Research Department for Limnology, Mondsee, University of Innsbruck, [email protected]
Rainer Kurmayer, Research Department for Limnology, Mondsee, University of Innsbruck, [email protected]

Abstract

In the past few decades Nyanza Gulf of Lake Victoria has shown severe signs of eutrophication by regular occurrence of cyanobacterial blooms dominated by the microcystin-producing buoyant colony-forming genus Microcystis spp. Cyanobacterial blooms in the Gulf have been associated with shutdown of water treatment, fish kills, and occurrence of microcystins in fish tissue. The eutrophication in the Gulf is partly associated with limited water exchange with the main lake basin after the construction of a Causeway in 1983 which blocked Mbita channel, that links the Gulf to the main basin besides Rusinga channel. In May 2017 the Mbita channel was partly reopened by a 150 m wide entrance to the main basin. It was expected that this dam (re)opening might increase the hydrological connectivity of the Gulf with the main basin and thus reduce phytoplankton growth by increased dilution effects. Monthly investigation on physical-chemical parameters, phytoplankton composition, and resulting cyanotoxins was done for a period of one year in 2017/2018. The study reports the changes in physicochemical parameters, spatial phytoplankton composition and cyanobacterial toxin concentrations in relation to hydrological changes in the Gulf. The study  contributes towards understanding water quality assessment and monitoring using spatio-temporal distribution  and composition of phytoplankton.