Abstract:

An effort to understand the composition and distribution of benthic invertebrate and fish communities as indication of water quality spectra in three bays: Murchison Bay associated with urban, Fielding Bay with semi-urban and Hannington Bay with rural catchment land use patterns in Victoria Basin is the main purpose of this thesis. In view of the dramatic ecological changes such as unprecedented loss of biodiversity and deterioration of water quality that have happened in Lake Victoria since 1960's, this study introduces biological monitoring as a tool for assessing water quality in Lake Victoria and its environs in the management of the basin waters. As initial recipients of watershed inputs, nearshore areas in the bays were the main focus of the study for assessing water quality changes and the associated macro-invertebrate and fish community components. Water quality and macro-invertebrate and fish assessments in nearshore areas of three bays were conducted eight times between June 2001 and May 2002 at three sites in the respective bays. The sites were Portbell, Nakivubo channel mouth and Kawuku in Murchison Bay; Kakira, Wanyange Masese and Wanyange in Fielding Bay; and Kitovu, Lwanika and Namavundu in Hannington Bay. The observed water quality, benthic macro-invertebrate and fish diversity and abundance variables were delineated within the bays and spatial patterns displayed on maps. Five chapters comprise this thesis. Chapter one offers a general introduction about Lake Victoria, its changes in water quality and fisheries and the conceptual background to thematic areas covered in the subsequent chapters. Chapter two illustrates the spatial patterns of water quality within and among bays relative to catchment urban rural land use and identifies patterns in trophic states. Chapter three defines spatial and temporal variation of composition and mean densities of benthic macroinvertebrates in the sampled areas of three bays, and use presence or absence of certain taxa to predict the trophic status relative to catchment land use gradient. Chapter four describes and compares at the sample sites, the composition of fish, fish diversity and abundance indices within and among bays. Chapter 5 is a general discussion and conclusions tying up possible correspondence between water quality and biota, and implications of biodiversity and environmental conservation of Lake Victoria ecosystem. The primary water quality results demonstrated that the extent of eutrophication was highest in Murchison Bay, moderate in Fielding Bay and least in Hannington Bay. The macro-invertebrate assemblage index was sensitive to escalating extent of eutrophication as noted in Murchison bay with low diversity (mainly comprised by Chironomus sp.