Browsing by Author "Lugomela, C."

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    The influence of physical-chemical variables on the spatial and seasonal variation of Chlorophyll-a in coastal waters of Unguja, Zanzibar, Tanzania
    (WIOMSA, 2018) Peter, N.; Semba, M.; Lugomela, C.; Kyewalyanga, M.S.
    Chlorophyll-a (Chl-a) concentrations were measured at four sites around Unguja, Zanzibar during the northeast (NE) and southeast (SE) monsoon seasons. Data for Chl-a, nitrate, phosphate, ammonia, dissolved oxygen, sea sur face temperature, pH and salinity were collected once a month from March 2008 to March 2009. The SE monsoon had insignificantly higher Chl-a compared to the NE monsoon season when Chl-a for Bawe, Chumbe, Pongwe and Mnemba were combined (W = 234, p = 0.93). The drivers of high Chl-a during the SE monsoon were ammonia and nitrate. Results from individual sites showed that Pongwe and Mnemba had higher median Chl-a during the SE than the NE monsoon season. Temperature, dissolved oxygen and ammonia were the major factors that influenced high Chl-a at these sites. In contrast, Chumbe and Bawe had higher median Chl-a during the NE- than the SE mon soon season. The major factors influencing high Chl-a in the NE at Chumbe and Bawe were high levels of nutrients, mainly from sewage effluent and various human activities around the coast in Zanzibar town. The interaction of Chl-a between monsoon seasons (NE and SE) and sites (Bawe, Chumbe, Pongwe and Mnemba) was insignificant (F(1,3) = 1.3144, p = 0.2949). The principal component analysis revealed that different physical and chemical environmental variables affect Chl-a concentration over time and location.
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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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    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.