Ecological modeling of Lake Victoria

Lake Victoria is of immense ecological and socio-economic significance for the riparian communities. However, the lake is faced with human induced pressures such as overfishing, introduction of alien species, increased eutrophication and climate change impacts. Its large spatial extent and complex ecology have also limited the understanding of the system dynamics, major processes, drivers and responses. To address this challenge, Atlantis, the first end-to-end whole ecosystem model for the lake was developed. First, a Regional Oceanographic Model System (ROMS) for the lake was developed to provide hydrodynamic forcing data for the ecosystem model. The ROMS model was based on real bathymetry, river runoff and atmospheric forcing data. Results from this model revealed diverse spatial and temporal water circulation patterns and temperature trends in Lake Victoria. The ROMS output provided water currents and temperature forcing data for the Atlantis model. The Lake Victoria Atlantis model was spatially resolved into 12 unique dynamic areas based mainly on their biophysical attributes. A total of 38 functional groups constituted the biological model while fishing was implemented by four fleets with different targeting options. The model was validated by fitting simulated output to available observational data sets. Simulations showed elevated nutrients and primary production in inshore areas and gulfs that can be linked to point sources of pollution and limited flushing. The model also revealed complex inter-specific relationships among the biological groups. For example, the introduced Nile perch (\emph{Lates niloticus}) exhibited a strong negative correlation with haplochromine cichlids (their prey) as well as most of other fish groups. This brings to fore the significance of predator-prey relationships and the impact of introduced species; information that is critical for effective fisheries and ecosystem management. The model was then used to simulate the impact of different fishing scenarios on the ecosystem. Scenarios tested included varied fishing pressure for Nile perch (the main predator at the top of the food chain), key prey species (haplochromines) and other species. The effects of these scenarios were tested using six common ecosystem-level indicators. Predictions showed that no particular scenario excels in all the six indicators. However, halting harvesting of haplochromines results in the best overall ecosystem performance. This scenario is projected to result in the highest yield of commercially important species and possibly cause minimal disruption to fishing activities. Findings of this study reinforce the need for an ecosystem approach to fisheries management in Lake Victoria.Viktoríuvatn er mikilvægt strandbyggjum sínum, vistfræðilega, félagslega og efnahagslega. Talsvert álag er á vistkerfið sakir ofveiði, innleiðingar framandi tegunda, mengunar og loftlagsbreytinga. Breytingar af þeim sökum, auk flókinnar vistfræði, hafa takmarkað möguleika á skilning á kerfinu sjálfu, helstu ferlum, áhrifavöldum og viðbrögð kerfisins við breytingum. Til að mæta þessari áskorun hefur heildstætt vistkerfislíkan (Atlantis) verið þróað fyrir vatnið. Sérstakt straumalíkan var þróað fyrir vatnið til að setja upp straumkerfi gögn fyrir vistkerfislíkanið. Straumalíkanið var byggt á upplýsingum um dýpi, rennsli áa ásamt upplýsingum um loftþrýsting og úrkomu. Straumkerfislíkanið sýndi hringrás vatns og þróun hitastigs í vatninu. Atlantis líkanið fyrir Viktoríuvatn inniheldur 12 svæði, byggt á líf- og eðlisfræðilegum eiginleikum. Notast var við 38 hópa lífvera og fjóra veiðiflota með ólíkt valmynstur. Líkanið var mátað við ýmis fyrirliggjandi gögn. Útreikningar sýna aukið magn næringarefna og frumframleiðslu, bæði á grunnslóð og dýpi, sem tengist þekktum uppsprettum mengunar og takmörkuðu gegnumstreymi. Í líkaninu komu einnig fram flókin tiltekin tengsl milli líffræðilegra hópa. Þannig sýndi Nílarkarfi sterka neikvæða fylgni við bráð (haplochromines) og raunar flesta hópa fiska. Þetta sýnir vel mikilvægi samspils afræningja og bráða auk áhrifa innfluttra tegunda og nauðsyn þess að líta á allt vistkerfið þegar v stjórna skal veiðum. Líkanið var síðan notað til að prófa áhrif mismunandi veiðistjórnunar á lífríkið. Sviðsmyndir voru m.a. breytilegt veiðiálag á Nílarkarfa (ránfiskur og efstur í fæðukeðjunni), lykilbráð (haplochromines) og aðrar tegundir. Áhrif sviðsmyndanna voru metin með sex algengum mælikvörðum. Niðurstöðurnar bentu ekki til þess að nein stjórnunaraðferðanna bæri af í öllum sex mælikvörðunum. Prófanir sýna hins vegar að sú aðferð að stöðva veiðar á helstu bráð gefi bestan almennan árangur. Hér fæst mestur afli úr efnahagslega mikilvægum stofnum og lágmarks röskun á veiðum. Niðurstöður rannsóknarinnar sýna vel þörfina fyrir vistkerfisnálgun við stjórnun fiskveiða í Viktoríuvatni.United Nation University - Fisheries Training Programm

High-resolution bathymetries and shorelines for the Great Lakes of the White Nile basin

This article is licensed under a Creative Commons Attribution 4.0 International License.HRBS-GLWNB 2020 presents the first open-source and high-resolution bathymetry, shoreline, and water level data for Lakes Victoria, Albert, Edward, and George in East Africa. For each Lake, these data have three primary products collected for this project. The bathymetric datasets were created from approximately 18 million acoustic soundings. Over 8,200 km of shorelines are delineated across the three lakes from high-resolution satellite systems and uncrewed aerial vehicles. Finally, these data are tied together by creating lake surface elevation models collected from GPS and altimeter measures. The data repository includes additional derived products, including surface areas, water volumes, shoreline lengths, lake elevation levels, and geodetic information. These data can be used to make allocation decisions regarding the freshwater resources within Africa, manage food resources on which many tens of millions of people rely, and help preserve the region’s endemic biodiversity. Finally, as these data are tied to globally consistent geodetic models, they can be used in future global and regional climate change models.ECU Open Access Publishing Support Fun

Lake Victoria Atlantis model output

This is a netcdf file with the Lake Victoria Atlantis model. There is a graph showing  the evolution of biomass of the biological groups used in the mode

Lake Victoria Hydrodynamics

This is ROMS for Lake Victoria output, validation data and gis mapping shape file

Observed and modeled vertical temperature profiles in Lake Victoria during the months of February and August 2008.

<p>Observed and modeled vertical temperature profiles in Lake Victoria during the months of February and August 2008.</p

Modeled 20 day averaged wind curl (vectors) in Lake Victoria in different seasons of 2008.

<p>Modeled 20 day averaged wind curl (vectors) in Lake Victoria in different seasons of 2008.</p

Simulation of Lake Victoria Circulation Patterns Using the Regional Ocean Modeling System (ROMS)

<div><p>Lake Victoria provides important ecosystem services including transport, water for domestic and industrial uses and fisheries to about 33 million inhabitants in three East African countries. The lake plays an important role in modulating regional climate. Its thermodynamics and hydrodynamics are also influenced by prevailing climatic and weather conditions on diel, seasonal and annual scales. However, information on water temperature and circulation in the lake is limited in space and time. We use a Regional Oceanographic Model System (ROMS) to simulate these processes from 1^st January 2000 to 31^st December 2014. The model is based on real bathymetry, river runoff and atmospheric forcing data using the bulk flux algorithm. Simulations show that the water column exhibits annual cycles of thermo-stratification (September–May) and mixing (June–August). Surface water currents take different patterns ranging from a lake-wide northward flow to gyres that vary in size and number. An under flow exists that leads to the formation of upwelling and downwelling regions. Current velocities are highest at the center of the lake and on the western inshore waters indicating enhanced water circulation in those areas. However, there is little exchange of water between the major gulfs (especially Nyanza) and the open lake, a factor that could be responsible for the different water quality reported in those regions. Findings of the present study enhance understanding of the physical processes (temperature and currents) that have an effect on diel, seasonal, and annual variations in stratification, vertical mixing, inshore—offshore exchanges and fluxes of nutrients that ultimately influence the biotic distribution and trophic structure. For instance information on areas/timing of upwelling and vertical mixing obtained from this study will help predict locations/seasons of high primary production and ultimately fisheries productivity in Lake Victoria.</p></div

Modeled 20 day verically averaged currents (vectors) in Lake Victoria in different seasons of 2008.

<p>Modeled 20 day verically averaged currents (vectors) in Lake Victoria in different seasons of 2008.</p

Map of Lake Victoria, its major rivers and bathymetry.

<p>Map of Lake Victoria, its major rivers and bathymetry.</p

The modeled daily averaged water temperature (shaded, in °C) and vertical velocity (contour, in cm/day and positive upward) in Lake Victoria in stratified (upper row) and isothermal (lower row) conditions in 2008.

<p>The west—east section (left) is along 1.0°S while the south—north section (right) is along 33.2°E.</p