William Okello

William Okello
National Fisheries Resources Research Institute, Jinja, Uganda · Limnology/Water Environment

PhD

About

26
Publications
8,214
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271
Citations
Additional affiliations
June 2006 - January 2010
Austrian Academy of Sciences (OeAW)
Position
  • PhD Student

Publications

Publications (26)
Article
Full-text available
Natural lakes are thought to be globally important sources of greenhouse gases (CO2, CH4, and N2O) to the atmosphere although nearly no data have been previously reported from Africa. We collected CO2, CH4, and N2O data in 24 African lakes that accounted for 49% of total lacustrine surface area of the African continent and covered a wide range of m...
Article
Full-text available
The paper describes a new genus and new species of Cyanoprokaryota, referred to Pleurocapsales incertae sedis-Cyanocystopsis kitagatae gen. et sp. nov. The new taxon is characterized by the presence of two different stages (filamentous, formed by spherical cells and stalked bundles of claviform cells). The branching of filaments, which leads to the...
Article
Full-text available
To ensure the long-term sustainable use of African Great Lakes (AGL), and to better understand the functioning of these ecosystems, authorities, managers and scientists need regularly collected scientific data and information of key environmental indicators over multi-years to make informed decisions. Monitoring is regularly conducted at some sites...
Data
This file includes information on the proposed parameters for the multi-lakes monitoring of the African Great Lakes (Appendix S2). This file is the Electronic Supplemental Material (ESM) of : Plisnier, P.-D., Kayanda, R., MacIntyre, S., Obiero, K., Okello, W., Vodacek, A., Cocquyt, C., Abegaz, H., Achieng, A., Akonkwa, B., Albrecht, C., Balagizi...
Article
Full-text available
The Nyanza Gulf of Lake Victoria is considered eutrophic with degrading water quality, as shown by harmful algal blooms formed by cyanobacteria of the genus Microcystis. The dilution of gulf water occurs mainly through the wide Rusinga Channel, whereas the much narrower and shallower Mbita Channel was reopened in May 2017. Specific conductivity and...
Article
Full-text available
1. Lake Victoria experienced a strong degradation of water quality between the 1960s and the 1990s and, as a consequence of eutrophication, the dominant phytoplankton group changed from diatoms to N2-fixing cyanobacteria and there was a 2- to 10-fold increase in Chlorophyll-a. The goal of this study is to determine whether the 2018-2019 physical- (...
Article
Full-text available
Eutrophication of Lake Victoria led to changes in its phytoplankton communities. However, different levels of eutrophication exist in the open lake and the bays, and between embayments. This study utilized spatial and temporal sampling of Napoleon Gulf and Murchison Bay, exhibiting different trophic conditions. Over one year, we investigated phytop...
Article
Zooplankton community constitutes one of the keystone organisms that are crucial in understanding aquatic ecosystem responses to environmental distresses. The objective of this study was to contribute to the understanding of zooplankton ecological conservation status and assessment of potential impacts of the proposed Hydropower plant on the zoopla...
Article
The unknown status of inland fish stocks hinders their sustainable management. Therefore, increasing stock status information is important for sustainable inland fisheries. Fisheries reference points were estimated for five exploited fish species (11 stocks) in the Lake Edward system, East Africa, which is one of the most productive inland water sy...
Article
Full-text available
Despite growing evidence that methane (CH4) formation could also occur in well-oxygenated surface fresh waters, its significance at the ecosystem scale is uncertain. Empirical models based on data gathered at high latitude predict that the contribution of oxic CH4 increases with lake size and should represent the majority of CH4 emissions in large...
Presentation
Full-text available
The extensive natural ecosystems of tropical Africa are a significant store of carbon, and play a key but uncertain role in the atmospheric budgets of carbon dioxide and methane. Recent studies of satellite observations have concluded that methane emissions from this geographical region have increased since 2010 as a result of increased wetland ext...
Preprint
Despite growing evidence that methane (CH4) formation could also occur in well-oxygenated surface freshwaters, its significance at the ecosystem scale is uncertain. Empirical models based on data gathered at high latitude predict that the contribution of oxic CH4 increases with lake size and should represent the majority of CH4 emissions in large l...
Article
Full-text available
We report a data set of dissolved organic carbon (DOC) concentration and dissolved organic matter (DOM) composition (stable carbon isotope signatures, absorption and fluorescence properties) obtained from samples collected in Lake Victoria, a large lake in East Africa. Samples were collected in 2018-2019 along a bathymetric gradient (bays to open w...
Presentation
Full-text available
The extensive forest ecosystems of tropical Africa are a significant store of carbon, and play a key but uncertain role in the atmospheric budgets of carbon dioxide and methane. Recent studies of satellite observations have concluded that methane emissions from this geographical region have increased since 2010 as a result of increased wetland exte...
Article
Africa is experiencing high annual population growth in its major river basins. This growth has resulted in significant land use change and pollution pressures on the freshwater ecosystems. Among them, the Lake Victoria basin, with more than 42 million people, is a unique and vital resource that provides food and drinking water in East Africa. Howe...
Article
Full-text available
Lake Edward is one of the African Rift Valley lakes draining into the Nile River basin. We conducted three sampling series in Lake seasonal conditions and in several sites varying by depth and proximity to river outlets, including the Kazinga Channel, which connects the hypertrophic Lake George to Lake Edward. The phytoplankton was examined using m...
Article
Full-text available
Lake Victoria in East Africa is a major ecosystem, whose size and importance has warranted the exploration of MODIS imagery to provide continuous and accurate water quality information. To this effect, two sea expeditions (in November 2014 and February 2015) were carried out to collect in situ lake surface temperature (LST), chlorophyll a (Chl) and...
Presentation
Full-text available
Unnoticed by the public, initiatives for oil exploration are advanced in Africa’s largest freshwater reservoirs, including Lakes Tanganyika, Malawi and lately Albert, threatening their ecosystems and biota. It is imperative that environmental impact assessments are conducted by independent organizations to ensure that decisions on this matter are b...
Article
Full-text available
As the world’s demands for hydrocarbons increase, remote areas previously made inaccessible by technological limitations are now being prospected for oil and gas deposits. Virtually unnoticed by the public, such activities are ongoing in the East African Great Lakes region, threatening these ecosystems famed for their hyper-diverse biota, includin...
Article
Full-text available
The Kyoga lake system, which is c. 4 m deep, originally had a diverse fish fauna, extensive macrophytes and wetlands. Most (82%) of its water comes from Lake Victoria, is controlled through three dams and has a short residence time of c. 3 months. Physical and chemical factors, plankton productivity and composition vary across the lake from east to...
Article
Full-text available
This study investigated the seasonal development of phytoplankton and potential microcystin (MC)-producing cyanobacteria and MC concentrations in freshwater lakes in Uganda. During 1 year (May 2007–April 2008), monthly measurements were made of chemical and physical characteristics, phytoplankton composition and MC concentrations in a hypertrophic...
Article
Full-text available
It is generally agreed that the hepatotoxic microcystins (MCs) are the most abundant toxins produced by cyanobacteria in freshwater. In various freshwater lakes in East Africa MC-producing Microcystis has been reported to dominate the phytoplankton, however the regulation of MC production is poorly understood. From May 2007 to April 2008 the Microc...
Article
Full-text available
Microcystins (MCs) are cyclic heptapeptides, which are the most abundant toxins produced by cyanobacteria in freshwater. The phytoplankton of many freshwater lakes in Eastern Africa is dominated by cyanobacteria. Less is known, however, on the occurrence of MC producers and the production of MCs. Twelve Ugandan freshwater habitats ranging from meso...
Article
Full-text available
Bench scale experiments were done to assess the effects of decomposition of water hyacinth on phosphorus release and water quality. Hyacinth plants from the lake were chopped to fine pieces. In replicate incubation tubes, 50 g of plant material was stocked to which 1.6 L of lake water was added. One set was aerated while the other was sealed with r...

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Projects

Projects (4)
Project
Inland waters (streams, rivers, lakes and reservoirs) are important players in the global budgets of long-lived green-house gases (GHGs), acting as vigorous sources to the atmosphere of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). Available data suggest that CH4 emissions from inland waters are highest at tropical latitudes although these are also the regions where data are dramatically scarce and urgently needed to improve accuracy of emission estimates. Available data suggest that CO2 emissions from rivers in tropical latitudes could also be higher than their temperate counterparts. However, tropical lakes could be sinks of atmospheric CO2, which would shift the paradigm that lakes are sources of CO2 to the atmosphere based on data-sets acquired at high- and midlatitudes. The main goal of the LAVIGAS project is to fill an enormous data gap by acquiring a seasonally and spatially resolved data-set of CO2, CH4 and N2O dissolved concentrations in Lake Victoria, the largest lake in the tropics and second largest in the World, where to our best knowledge no data are available on the dissolved concentration of these GHGs. The data-set will allow to compute the GHG fluxes with the atmosphere, and the analysis with ancillary data (O2, nutrients, phytoplankton pigments, organic matter concentration and stable isotopic composition) will also allow todecipher the biogeochemical processes that control the temporal variability and the spatial distribution of these GHGs. Data will also be analysed withdata-sets that are methodologically consistent obtained by our group in other African lakes (Kivu, George, Edward). The project builds on a successful on-going collaboration with the National Fisheries Resources Research Institute (NaFIRRI) on Lake Edward (BELSPO project HIPE).
Archived project
The WaSAf programme (Monitoring and Sustainable Management of Surface Freshwater Sources in Africa) deals with the elaboration of long-term monitoring programs in order to facilitate the sustainable management of surface freshwater resources used (or planned to be used) for drinking water supply in three African countries : Lac de Guiers (Sénégal), Murchinson bay (lake Victoria in Uganda) and Aghien lagoon (Ivory Coast). These three cities share a very high population growth and consequently an increase in their demand for safe water. But the fresh water ecosystems have experienced a decrease in their water quality in the 20 past years as illustrated for example by the occurrence of recurrent cyanobacterial blooms in each of them. The global aims of the Wasaf project is to evaluate the ecological status of these ecosystems and the trends in the evolution of this status in the next years, to implement long term monitoring programs on these resources, to evaluate what are the pressures acting on them and how these pressures have an impact on the water quality and to prepare actions for their protection and/or their restoration. The already available knowledge on the three ecosystems and the actions already implemented for their monitoring and protection are very heterogeneous. Moreover, the geographical and institutional contexts are also very different from one country to another one, which will provide the opportunity for scientists and stakeholders to compare and exchange experience and to built a network on the monitoring and the protection of surface water resources in Africa.
Project
To ensure the long-term sustainable use of African Great Lakes (AGL), and to better understand the functioning of these ecosystems, authorities, managers and scientists need regularly collected scientific data and information of key environmental indicators over multi-years to make informed decisions. Monitoring is regularly conducted at some sites across AGL; while at others sites, it is rare or conducted irregularly in response to sporadic funding or short-term projects/studies. Managers and scientists working on the AGL thus often lack critical long-term data to evaluate and gauge ongoing changes. Hence, we propose a multi-lake approach to harmonize data collection modalities for better understanding of regional and global environmental impacts on AGL. Climate variability has had strong impacts on all AGL in the recent past. Although these lakes have specific characteristics, their limnological cycles show many similarities. Because different anthropogenic pressures take place at the different AGL, harmonized multilake monitoring will provide comparable data to address the main drivers of concern (climate versus regional anthropogenic impact). To realize harmonized long-term multi-lake monitoring, the approach will need: (1) support of a wide community of researchers and managers; (2) political goodwill towards a common goal for such monitoring; and (3) sufficient capacity (e.g., institutional, financial, human and logistic resources) for its implementation. A paper presents an assessment of the state of monitoring the AGL and possible approaches to realize a long-term, multi-lake harmonized monitoring strategy. This paper's title is "Need for harmonized long-term multi-lake monitoring of African Great Lakes" and is available here (+ supplementary material). Key parameters and measurement frequency have been discussed by a wide community and are proposed. The national and regional authorities will of course decide on the possible implementation. Those correspond closely to the goals of the African Union’s blue economy objectives. If you are interested, please complete this survey https://www.agl-acare.org/monitoring-survey-1-en This would be helpfull to develop this proposal. Thank you !