College of Agricultural Sciences and Fisheries Technology
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Browsing College of Agricultural Sciences and Fisheries Technology by Subject "Africa"
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Item Cyanobacterial Diversity and Nitrogen Fixation in Coastal Areas around Zanzibar, Tanzania(Schweizerbart, 2001) Lugomela, Charles; Bergman, Birgitta; Waterbury, J.Cyanobacterial diversity and nitrogen fixation were examined in coastal areas around Zanzibar, Tanzania. Samplings were performed intermittently from June 1997 to October, 1999 from plankton, intertidal and subtidal microbial mats as well as from epiphytes on seagrasses and seaweeds. A total of 21 cyanobacterial genera comprising 50 species are described, out of which 64% were filamentous non-heterocystous forms, 24% heterocystous forms and 12% unicellular forms. Non-heterocystous Oscillatoria spp. dominated the microbial mats and epiphytic habitats, and the like-wise non-heterocystous Trichodesmium spp. were the most abundant cyanobacteria in net samples. Fourteen of the species identified were analyzed for the ability to fix dinitrogen using the acetylene reduction assay and eleven species showed nitrogenase activity. Six of these species were also subjected to immuno-blotting. The presence of a nitrogenase (Fe-protein) protein with an average molecular weight of 36 kDa was detected. The results suggest higher cyanobacterial diversity in the area investigated than previously reported and indicate that the capacity to fix molecular nitrogen is present in a number of species that are often prominent in these habitats. It is therefore concluded that cyanobacteria may have an important role and may contribute to new N-production in coastal areas of Tanzania.Item Environmental Assessment of Mercury Contamination from the Rwamagasa Artisanal Gold Mining Centre, Geita District, Tanzania(Elsevier, 2005-05) Taylor, H.; Appleton, J. D.; Lister, R.; Smith, B.; Chitamweba, D.; Mkumbo, O.; Machiwa, John F.; Tesha, A. L.; Beinhoff, C.This study presents the results of an environmental assessment of mercury (Hg) contamination in the Rwamagasa artisanal gold mining area, northwest Tanzania, and the potential downstream dispersion along the River Malagarasi to Lake Tanganyika. At the time of sampling, generally low concentrations of Hg (<0.05 mg/kg) occurred in most cultivated soils although higher Hg (0.05-9.2 mg/kg) was recorded in urban soils and vegetable plot soils where these are impacted by Hg-contaminated water and sediment derived from mineral processing activities. Hg in vegetable and grain samples is mostly below the detection limit of 0.004 mg/kg Hg, apart from 0.007 and 0.092 mg/kg Hg in two yam samples and 0.011 to 0.013 mg/kg Hg in three rice samples. The standardized (i.e., standardized to 10 cm length) Hg concentrations in Clarias spp. increase from about 0.01 mg Hg/kg for the River Malagarasi delta to 0.07, 0.2, and 1.6 mg/kg, respectively, for the Rwamagasa 'background', moderately and most contaminated sites. For piscivorous (Lates, Brycinus, and Hydrocynus spp.), insectivorous (Barbus spp.), and planktivorous (Haplochromis spp.) fish species, the 10-cm standardized Hg concentrations increase from about 0.006 mg/kg for the River Malagarasi-Lake Tanganyika area to 0.5 and 3.5 mg/kg, respectively, for the Rwamagasa moderately and most contaminated sites. The low concentrations of Hg in fish from the Malagarasi River delta and Lake Tanganyika indicate that Hg contamination from the Rwamagasa area does not have a readily discernible impact on the biota of Lake Tanganyika. Many of the fish samples from Rwamagasa exceed guidelines for human consumption (0.5 mg/kg) as well as the WHO recommended limit for vulnerable groups (0.2 mg/kg). Tissue total Hg (THg) of all fish collected from the River Malagarasi-Lake Tanganyika subarea is well below these guidelines. Potential human exposure through consumption of 300 g/day of rice grown on Hg-contaminated soils is 5.5 microg/week. Consumption of 250 g Nile perch (Lates spp.), 500 g tilapia (Oreochromis spp.), and 250 g of catfish (Clarias spp.) each week would result in an intake of 65 microg Hg/week for people consuming only fish from the Mara and Mwanza regions of Lake Victoria and 116 microg Hg/week for people in the Rwamagasa area consuming tilapia and Nile perch from Lake Victoria and catfish from mining-impacted streams. This is lower than the Provisional Tolerable Weekly Intake (PTWI) of 300 microg for Hg in the diet set by the WHO and the FAO. Inadvertent ingestion of soil containing 9 mg Hg/kg at a rate of 80 mg/day would give an additional estimated weekly intake of 5 microg THg, whereas the persistent and purposeful consumption of soil (geophagia) at a rate of 26 g soil/day would produce an additional chemical exposure of 230 microg Hg/day.Item Target strength measurements of Nile perch (Lates niloticus: Linnaeus, 1758) in Lake Victoria, East Africa(2012) Robert, Kayanda; Inigo, Everson; Taabu, Munyaho; Mgaya, Yunus D.Results of estimation of target strength (TS) of physoclistous Nile perch using in situ TS measurements and deformed cylinder model (DCM) at 70 and 120kHz are presented. The results of the two methods are compared with those from cage experiments conducted between 1999 and 2000. Cage experiments that assumed the 20 Log(L) relationship (TS = 20 Log(TL) - 66.55) provided a good fit only over the length range of 18-38 cm total length, but overestimated the length of large fish (>60cm TL). The DCM which lead towards a 30 Log(L) provides more accurate conversion over the full length range of single targets. An in situ study that made no assumptions about the shape, structure or orientation of the fish provided a close fit of acoustically estimated length frequency distributions to net hauls with the equations: It is suggested that using this approach can provide valid TS to length relationships for acoustic surveys on species for which little information exists and there is little opportunity for direct observation of behavioural aspects that are known to affect TS such as tilt angle and vertical migration.