African Journal of Tropical Hydrobiology and Fisheries

Spatial Distribution and Potential Risks of Mercury in Surficial Sediments of the Kenyan Waters of Lake Victoria

Job Mwamburi — Wed, 20 Jun 2018 00:00:00 +0000

Mercury is among the potentially harmful elements of concern globally, with known toxicity and potential for bio-magnification in aquatic food webs.In Lake Victoria, initial sediment core total Hg data has been provided, but THg distribution in Nyanza gulf are not well known, despite the available data from Napoleon gulf, Uganda, and its reported occurrences around gold mining areas. Surficial lake sediments were collected in 2012 and 2010 (from 26 and 24 sites respectively) from the Kenyan portion of Lake Victoria (East Africa) and the sedimentary characteristics and THg contents determined. The detectable THg concentrations had a spatial mean (±standard deviation) of 167±21ng/g dry weight. Surficial sediments contained high organic matter contents, which were positively correlated to THg. The sediments enrichment factors ranged from 0.4 to 33.8 showing anthropogenic effects although levels measured were similar to those found in other lakes. An assessment of the potential ecological effects for bottom dwelling organisms was made based on the mercury concentrations. There is need of continued awareness creation on improved waste management and treatment technologies, and the use of better techniques in Au mineral processing.

Keywords: Lake Victoria, Mercury concentration, Nyanza gulf, Sediment quality, Surficial sediments

Evidence of eutrophication in the Tanzania sector of Lake Victoria

Omari I. Myanza, Rosemary Rwebugisa, Omari Mwinjaka — Wed, 20 Jun 2018 00:00:00 +0000

Lake Victoria has experienced accelerated eutrophication with elevated phosphorus, nitrogen and chlorophyll-a concentrations, coupled with decreased transparency as a result of the growing human activities in the catchment area. A survey in Tanzanian waters from 2011-2016 provided data on phosphorus, nitrogen, dissolved oxygen and transparency from littoral (bays and gulfs) and pelagic stations. The differences between the two groups of stations were generally small, with the exception of chlorophyll-a, which was generally higher at the littoral stations. The molar TN:TP ratio indicated nitrogen limitation in most of the lake thus favouring the dominance of nitrogen-fixing cyanobacteria, which currently dominate the phytoplankton. The trophic status of the lake was assessed using the OECD criteria, yielding four ‘eutrophic’ and two ‘hypertrophic’ assessments. A similar assessment in 2005-2005 gave two ‘eutrophic’ and four ‘hypertrophic’ classifications, suggesting that the lake may have not deteriorated over the last decade and may have stabilised.

Keywords: Eutrophication, Lake Victoria; Nitrogen, Phosphorus, Transparency, Trophic status

Heavy metal contamination at dumpsites at Eldoret, Kenya, in the Lake Victoria Basin

This study assessed the heavy metals concentrations in municipal solid wastes at Eldoret Mwenderi dumpsites located at the shores of river Sosiani within the Lake Victoria Basin, Kenya. Concentrations of the three heavy metals analysed (lead, arsenic and cadmium) in water and leachate were higher than the WHO acceptable standards. Lead concentrations in solid wastes were slightly above East African acceptable standards but well above the US EPA compost standards. The wastes dumped in this site are not sorted and the dumpsite lacks a leachate collection and removal system. Lack of composite liners at the bottom and side of the dumpsite allow leachates to move into the ground water around the dumpsite. These metals are a potential threat to Lake Victoria and regular monitoring of ground and surface water of the surrounding area should be done to detect any heavy metals escaping the dumpsite.

Keywords: Heavy metals; Leachate; Management; Pollution; Wastes

A Review of Co-Management Interventions in the Lake Victoria Basin, Tanzania

William. J.S. Mwegoha

This paper presents appraisal of Co-Management Interventions (CMI) focusing on their successes and challenges associated with the environmental and social aspects carried out as part of the Lake Victoria Environmental Management Project, Phase Two (LVEMP-II) in Tanzania. A total of 23 sub-projects were appraised in accordance with the Environmental Management Act in four regions in Tanzania. The effectiveness of the appraisal process, including involvement of different parties, was assessed during the whole project cycle. Long delays in the process by the National Environment Management Council have often created a time conflict with the implementation schedule falling behind and delaying projects. Challenges relating to policy, regulatory and institutional issues for selected projects are discussed and recommendations for refining the assessment process are made.

Keywords: Environmental impact assessment, Planning, Reviews, Stakeholder consultation

The Potential of Anaerobic Digestion for Managing the Organic Fraction of Municipal Solid Waste: The Case of Kisumu City

Austin Omutto

The city of Kisumu, Kenya, generates about 400 t/day of solid waste of which 60% is organic. Most of this waste is deposited in undesignated dump sites, posing an environmental threat from methane emissions. Solid waste management is a major challenge in Kisumu and will worsen as the population grows. This paper explores the practicality of treating the city’s organic waste by anaerobic digestion as a means of waste management and energy production in the form of biogas. Since 1 tonne of organic waste produces 110 m3 of biogas, Kisumu could potentially produce 26,400 m3/day of biogas and as 1 m3 of biogas produces 2 kWh of electricity Kisumu could generate 52,800 kWh/day. In addition, 1 tonne of organic waste emits 1102 kg CO2 equivalent into the atmosphere but when converted to biogas through anaerobic digestion this is reduced to 181kg CO2e. Embracing anaerobic digestion would therefore provide a permanent, viable long-term solution to the management of organic waste with both environmental and economic benefits.

Keywords: Anaerobic digestion, Biogas, CO2 equivalent, Electricity, Environment, Organic waste

Impacts of Human Activities on Biodiversity of the Simiyu Wetland, Tanzania

Anna Masasi, Alfred Gobolo, Ignath Rwiza

Human activities such as intensive agriculture, grazing and settlements have degraded the ecological integrity of biotic communities in the Simiyu wetland by altering niche in terms of quality and quantity leading to a loss of biodiversity. Monitoring of vegetation types, game animals and bird species was carried out to determine the impact of human activities in the wetland. Biodiversity monitoring of Simiyu wetland showed an increase of species richness, abundance and diversity. Granivorous bird species increased by 18% while waterbirds decreased by 6% between 2010 and 2016. Similarly, invasive plant species increased by 42%, heavy feeders by 55% and shallow feeders by 26% between 2010 and 2016. The increase in granivorous bird species, invasive and heavy feeders indicate degradation of the wetland. Restoration of ecological character and management measures to Simiyu wetland are required in order to restore the values and functions of the wetland.

Keywords: Biodiversity, Birds, Habitat, Human activities, Vegetation