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Management implications of the physical limnological studies of Rusinga Channel and Winam Gulf in Lake Victoria

Sun, 01 Jan 2006 00:00:00 GMT

Title: Management implications of the physical limnological studies of Rusinga Channel and Winam Gulf in Lake Victoria Authors: Romero, J.R.; Alexander, R. Abstract: During April, May and August 2005 intensive field investigations were undertaken to characterize the physical limnology of Winam Gulf and Rusinga Channel regions of Lake Victoria in Kenya. Both the field data and numerical simulations with the three-dimensional (3D) hydrodynamics model, ELCOM (Estuary, Lake and Coastal Ocean Model), during these two field studies led to two major conclusions. First, though water currents in Rusinga Channel can be quite large (ca. 10-50 cm s-1), exchange through the channel is low because the tidal-like oscillations result in low net transport over a 24 hour period. Second, Winam Gulf can be segmented into four regions, two of which have relatively low flushing rates as compared to time scales of biogeochemical processing. Regionally, on the basis of these physical limological findings the implications for water quality management strategies for Winam Gulf are presented. Internationally, the role of Winam Gulf as a net source or sink of nutrients and pollutants to the open waters of Lake Victoria is addressed.

Systematics and distribution of zooplankton in Lake Victoria basin, Kenya

Sun, 01 Jan 2006 00:00:00 GMT

Title: Systematics and distribution of zooplankton in Lake Victoria basin, Kenya Authors: Masai, D.M.; Omondi, R.; Owili, M. Abstract: Zooplankton samples were collected, using a 60~km nansen net, from Lake Victoria (Kenya) and adjacent water bodies with emphasis being placed on the different habitats within the ecosystems. A total of 116 species were identified, 63 rotifers, 24 cladocerans and 29 copepods. A number of these were new records for the zooplankton fauna for the country.

Distribution and association of Tilapine unit stocks in the Lake Victoria catchment (Kenya)

Sun, 01 Jan 2006 00:00:00 GMT

Title: Distribution and association of Tilapine unit stocks in the Lake Victoria catchment (Kenya) Authors: Jembe, B.T.; Boera, P.N.; Okeyo Owuor, J.B. Abstract: The Lake Victoria Catchment (Kenya) harbours six species of tilapia. Two species Oreochromis variabilis (L) and Oreochromis esculentus (L) are endemic while four species Oreochromis niloticus, Oreochromis leucostictus, Tilapia zillii(Gervais) and Tilapia rendalli(Gervais) were variously introduced in 1950s and early 1960s. The existence of six tilapia species in the same geographical range has had significant ecological and economical implications. The study investigated the ecological impacts by determining species diversity, distribution, association (allopatric, sympatric and parapatric) and habitat preferences for the six-tilapia species. Shannon-wiener index was used to determine diversity, while species distribution was evaluated on the basis of 39 habitats (dams and satellite lakes) within the catchment. Species associations were determined using Cole’s Cab index. The Shannon Weiner function values of 2.44-2.7 indicate relatively high species diversity in 15% of 33 habitats where Tilapia were resident. Cole’s Cab indices showed significant relationships in O. esculentus X O. variabilis, O.leucostictus X O. esculentus, O. niloticus X O. variabilis and O. niloticus X O. leucostictus at P < 0.05. Habitat preference for the six species is provided.

The effect of turbid inflows into Winam Gulf, Lake Victoria: a 3D modeling study with ELCOM-CAEDYM

Sun, 01 Jan 2006 00:00:00 GMT

Title: The effect of turbid inflows into Winam Gulf, Lake Victoria: a 3D modeling study with ELCOM-CAEDYM Authors: Njuguna, H.; Romero, J.R.; Khisa, P. Abstract: The catchment of Winam Gulf in Kenya supports a population of 4.5 million inhabitants. Much of the population practices subsistence agriculture in the catchment that has led to high rates of sediment erosion and ultimately highly turbid rivers. Hence, every year during the two equatorial wet seasons, large quantities of catchment sediments are deposited into Winam Gulf. In Apr.-May 2005 an intensive field investigation was undertaken to determine the exchange dynamics between the northeastern offshore waters of Lake Victoria and Winam Gulf through Rusinga Channel. One of the outcomes of this scientific study was the validation of ELCOM (Estuary, Lake and Coastal Ocean Model), a three-dimensional (3D) hydrodynamics model, over Rusinga Channel and Winam Gulf. CAEDYM (Computational Aquatic Ecological DYnamic Model) is a water quality model that can be readily linked to ELCOM. In this modeling study we linked ELCOM and CAEDYM to evaluate the transport and fate of riverine sediments in Winam Gulf from several of the large rivers. Several size classes of suspended solids were evaluated. The extent and concentrations of sediment plumes were modeled over a range of riverine discharge. Further, simulations were run with reduced riverine sediment concentrations to evaluate the effect of turbidity levels in Winam Gulf if catchment improvement practices were implemented. This study illustrates that application of coupled 3D hydrodynamic and water quality models can serve to improve understanding of sediment plume dynamics in tropical lakes.