Browsing by Author "Muzuka, Alfred N. N."

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    Impact of hydrographic parameters and seasonal variation in sediment fluxes on coral status at Chumbe and Bawe reefs, Zanzibar, Tanzania
    (Elsevier, 2010) Muzuka, Alfred N. N.; Dubi, Alfonse M.; Muhando, Christopher A.; Shaghude, Yohanna W.
    Coral reefs which are an important resource to coastal communities and nation at large are adversely affected by rate of sediment flux to the reefs. However, there is little information on seasonal trend in sediment flux and its impact at the reefs off Zanzibar. Two years’ monthly data on sedimentation at Chumbe and Bawe reefs were used to assess seasonal variability in sediment flux and its implication on the coral status. Sediment flux to the Bawe reefs for the duration of the study ranged from 0.2 to 41.5 mg cm 2 d 1, while it ranged from 0.8 to 65.8 mg cm 2 d 1 at the Chumbe reefs. Sediment fluxes at Bawe reefs were highest between November and March, while they were highest between April and September at Chumbe reefs. Generally, sediment fluxes at Bawe reefs were low compared to those at Chumbe. The total sediment input to the reefs ranged from 4615 to 123,403 kg d 1 for Bawe reefs and 2750 to 79,636 kg d 1 for Chumbe reefs. High sediment fluxes at Bawe reefs between November and March; and the Chumbe reefs between April and September can be attributed to water currents and wind pattern in the east African region which are under the influence of the monsoons. The observed trend suggests that the period for coral transplant as a management option for the two sites should be different. Coral transplant can be undertaken in such a way that stress of the corals due to sedimentation can be felt after they have overcome stress from transplant process and temperature. The results from this study contribute to the much needed information for coral transplant, restoration, and management.
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    Phytoplankton and Nutrients Studies in Magu bay, Speke gulf, Lake Victoria, (Tanzania) following the 2001 principal Rain Season
    (University of Dar Es Salaam, 2005) Machiwa, John F.; Lugomela, C.; Muzuka, Alfred N. N.
    Phytoplankton abundance and species composition in relation to some physico-chemical parameters were studied in Magu Bay, Lake Victoria, in May 2001. Investigations on the influence of Simiyu River on the biological and physical characteristics of the Bay were carried out. Surface and bottom currents flowed in the northeast direction close to the river mouth but were completely reversed after about 1.5 km from the river mouth. Most suspended particles brought in by the river were deposited within 0.5 km after entering the lake. Nutrient concentrations were generally high towards the eastern part of the bay as compared to the rest of the bay area probably due to the reversal in the direction of current flow. Phytoplankton were generally dominated by the cyanobacteria Microcystis and Anabaena species though the diatoms Nitzschia and Melosira species were more abundant in some sampling stations. Phytoplankton abundance ranged from 500 cells ml-1 at stations LV36 and LV37 to 1440000 cells ml-1 at station LV1. The high abundance encountered at stations LV1, LV2, and LV3 is assumed to be due to formation of surface scum of the gas vacuolated Microcystis cells as a result of wind action. Phytoplankton production was possibly light limited in areas with simultaneously high nutrient concentrations and high turbidity. More data are required to corroborate the current study and to have a full picture of the influence of the river during different seasons.
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    Preliminary investigation on the Pleistocene/Holocene Sea-Level Changes along the Coastline of Tanzania, with reference to Unguja and Pemba Islands
    (2007) Muzuka, Alfred N. N.; Nyandwi, Ntahondi; Shaghude, Yohanna W.
    Along the coast of Tanzania, coral reefs, marine terraces and beach ridges are among the most important geomorphological features indicative of the Pleistocene/Holocene sea level changes. Three major terrace units can easily be identified on the mainland coast, namely, Mtoni (youngest), Tanga and Sakura (oldest). Three terrace units have also been identified on the Islands of Unguja and Pemba. On the basis of the difference in the terrace elevations between the two terrace systems it is postulated that the marine terraces on the islands probably represent minor fluctuations of sea level, rather than major phases of sea level fluctuation. A sand beach on the seaward side and several sand ridges on the landward side represent the Recent phase. The oldest Palaeoshoreline is approximately 5 m above the present sea level, and extends landward to more than 1 km. Specific localities around the two islands where Pleistocene/Holocene sea level changes has been preserved in the form of marine terraces and/or beach ridges include Chwaka, Uroa, Jambiani, Paje and Nungwi (Unguja island) and Vumawimbi and Kiuyu (Pemba island).
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    Preliminary investigation on the Pleistocene/Holocene Sea-Level Changes along the Coastline of Tanzania, with reference to Unguja and Pemba Islands
    (2003) Muzuka, Alfred N. N.; Nyandwi, Ntahondi; Shaghude, Yohanna W.
    Along the coast of Tanzania, coral reefs, marine terraces and beach ridges are among the most important geomorphological features indicative of the Pleistocene/Holocene sea level changes. Three major terrace units can easily be identified on the mainland coast, namely, Mtoni (youngest), Tanga and Sakura (oldest). Three terrace units have also been identified on the Islands of Unguja and Pemba. On the basis of the difference in the terrace elevations between the two terrace systems it is postulated that the marine terraces on the islands probably represent minor fluctuations of sea level, rather than major phases of sea level fluctuation. A sand beach on the seaward side and several sand ridges on the landward side represent the Recent phase. The oldest Palaeoshoreline is approximately 5 m above the present sea level, and extends landward to more than 1 km. Specific localities around the two islands where Pleistocene/Holocene sea level changes has been preserved in the form of marine terraces and/or beach ridges include Chwaka, Uroa, Jambiani, Paje and Nungwi (Unguja island) and Vumawimbi and Kiuyu (Pemba island).
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    Recent Trends in Accumulation Rate, Elemental and Isotopic Composition of Organic Matter in the Magu Bay, Lake Victoria
    (University of Dar Es Salaam, 2005) Muzuka, Alfred N. N.; Machiwa, John F.; Lugomela, C.
    Stable isotope composition of organic carbon (OC), 14C data, OC and nitrogen content of recently deposited sediments in Magu Bay of Speke Gulf, Lake Victoria are used to document accumulation rates, sources and distribution of organic matter in the bay. The stable isotope values of both organic carbon and nitrogen decrease towards offshore, and this trend is associated with increase in the contents of organic carbon and nitrogen. The isotope results show that the organic material deposited in the bay are generally derived from C4 type of plants and are not transported far from the river mouth. Also the results show that preservation of organic matter is high in open water probably due to high primary productivity owing to high concentration of nutrients and low in turbidity. Low isotope values in offshore sites indicate that the available stock of nutrients far exceeds the demand. Sedimentation rates in the bay are not high and range from 5 to 54 cm/ka. This could be attributed to trapping efficiency by shoreline aquatic macrophyte. Furthermore, the mean accumulation rates of organic carbon and nitrogen for the bay, range from 6.92 to 57.25 gC/m2/yr and 0.51 to 4.37 gN/m2/yr, respectively, and show that Magu Bay is currently experiencing eutrophication.
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    Sediment sources and their Distribution in Chwaka Bay, Zanzibar Island
    (WIOMSA, 2007) Muzuka, Alfred N. N.; Shaghude, Yohanna W.; Wannäs, Kjell O.; Nyandwi, Ntahondi
    This work establishes sediment sources, character and their distribution in Chwaka Bay using (i) stable isotopes compositions of organic carbon (OC) and nitrogen, (ii) contents of OC, nitrogen and CaCO3, (iii) C/N ratios, (iv) distribution of sediment mean grain size and sorting, and (v) thickness of unconsolidated sediments. The Chwaka Bay is located on the eastern coast of Zanzibar Island and is about 50 km2. It is a shallow partly sheltered lagoon with large intertidal area and fringing mangrove forest. The stable isotope values of nitrogen and OC, which averages 1.5±0.9‰ and -17.5±2.3‰ respectively, increases offshore indicating decrease in the influence of terrestrial material. Furthermore, nitrogen isotope values ranging from 0.3 to 3.9% suggest that the values result from nitrogen fixing plants. Because the bay has high abundance of calcareous green algae Halimeda plants, most likely low δ15N values reflect the influence of this photosynthetic plant to the total sediment budget. This inference is supported by low C/N ratio values that averages 7.9 ± 1.4 and with highest values being confined close to the mangrove forest. The contents of OC and nitrogen, which averages 0.75±0.60% and 0.11±0.08% respectively, are highest close to the mangrove forest. The sediment thickness in the Bay is higher in the northern part than in the southern part. The character of sediments in terms of grain size differs between eastern and western parts of the Bay. The eastern part is characterized by medium to fine white carbonate sand with mean grain size higher than 2φ, whereas coarse sediments with mean values less than 2φ characterize the western part. The content of calcium carbonate is very high with values being higher than 90% for the whole Bay owing to high concentration of carbonate sand-forming Halimeda.