African Journals Online
Tanzania Journal of Science

Volume 26 2000
Abstracts

SUBSIDENCE HISTORY OF THE RUKWA RIFT IN SOUTH WEST TANZANIA ANALYSED FROM IVUNA WELL
EI Mbede
Department of Geology, University of Dar es Salaam, 
P.O. Box 35052, Dar es Salaam, Tanzania.

ABSTRACT
The variation in subsidence rate during rift basin development is a good indication for the Geodynamic history of a sedimentary basin. The sedimentary section of Ivuna Well is herein used to explain the structural evolution of Rukwa Basin within the Western Rift of the East African Rift System. The sedimentary record of Ivuna Well is extracted from published information. The effects of sedimentary load, corrected for compaction and variation in water depth, and lake-level have been removed to obtain the "tectonic subsidence." Curves show two phases of accelerated subsidence related to the fault controlled rifting phases: The Karoo rifting and the Late Cenozoic rifting. Though several phases of rifting are proposed within Karoo time in eastern and southern Africa, it is difficult, with the present information from Ivuna well, to infer them. But the change of gradient of the Geohistory plots within the Karoo section does suggest at least variations of sedimentation rates. The Karoo rifting phase is followed by a steady subsidence which resulted from thermal contraction of the lithosphere thinned during Karoo crustal and lithospheric stretching, while Late Cenozoic rifting is still young at its initial phase of rifting (t = 0).

d13C SIGNATURES OF FLORA, MACROFAUNA AND SEDIMENT OF A MANGROVE FOREST PARTLY AFFECTED BY SEWAGE WASTES

JF Machiwa
Department of Zoology and Marine Biology, University of Dar es Salaam
P. O. Box 35064 Dar es Salaam, Tanzania.

ABSTRACT
Stable carbon isotope ratios (d13C) of sediments, suspended particulate matter, and crab gut content from Maruhubi mangrove forest, Zanzibar, were determined. Stable carbon isotope ratios were used to determine sources of organic matter in the forest. Mangrove organic carbon (d13C±SD = - 27.97±0.25) was found to be an important component of the sediment organic matter except at the marine fringe zone (d13C±SD = - 17.26±0.83). The areal distribution of d13C values show that the marine fringe zone was rich in organic carbon of marine origin. The terrestrial fringe zone was dominated by a mixed source of sediment organic carbon (d13C±SD =-24.89± 0.72). Vertical variations in d13C were not so obvious, showing a diminishing importance of mangrove organic matter below 60 cm in the sediments of the terrestrial fringe zone. Stable carbon isotope ratios of the major primary producers in the mangrove forest were reflected to a reasonable extent in the terrestrial fringe surficial sediment organic carbon. Stable carbon isotope ratios for plant and sediment organic carbon gave values in the range of - 27.67 to - 28.31 o/oo for mangroves and - 17.57 to - 24.89 o/oo for surface sediment (0 - 5 cm). Marine fringe sediments receive organic matter of marine origin to a large extent, in comparison to terrestrial fringe sediments, which contain mainly organic matter of mangrove origin.

HEAVY METALS AND ORGANIC POLLUTANTS IN SEDIMENTS OF DAR ES SALAAM HARBOUR PRIOR TO DREDGING IN 1999

JF Machiwa
Department of Zoology and Marine Biology, University of Dar es Salaam
P.O. Box 35064 Dar es Salaam, Tanzania

ABSTRACT
Heavy metals and organic contaminants were analysed in the sediments of the inner area of the Dar es Salaam harbour. Complementary analytical parameters, such as, the organic carbon content and the silt/clay fraction of the sediments showed good positive correlation (r = 0.64). Stations that had high content of fine grain material in the sediment also indicated relatively high level of organic carbon and pollutants. The Florida criteria (MacDonald 1993) for assessment of pollution of tropical marine sediments was adopted in oredr to evaluate the extent of pollution in Dar es Salaam harbour sediments. The Florida criteria is one of the established references for sediment quality assessment. Heavy metals that had concentrations above the Florida no effect level were chromium, copper, lead, mercury and zinc. Mercury exceeded the Florida no effect level (0.1 mgkg-1) at 18 of 22 sampling stations, but the Florida probable effect level (1.4 mgkg-1) was not closely reached at any station. Lead and chromium exceeded the Florida no effect level (21 mgkg-1and 33 mgkg-1respectively) at 15 stations. Copper and zinc exceeded the Florida no effect level (28 mgkg-1and 68 mgkg-1respectively) at 12 and 16 stations respectively. Levels of pollutants in the study area were generally lower than in the sediments of some major harbours of the world.

THERMOGRAVIMETRICAL STUDY OF GADOLINIUM CHLOROTUNGSTATE IN AIR BETWEEN 25 AND 1500°C


FN Ngassapa
Department of Chemistry, University of Dar es Salaam
P. O. Box 35061, Dar es Salaam, Tanzania

and

NU Venskovskii
Russian Peoples Friendship University, Moscow , Russia

ABSTRACT
Using DTA, X-ray powder diffraction, chemical and optical methods, the thermostability of Gd3WO6Cl3 was investigated. The compound was relatively stable on heating in air up to 710oC. Above this temperature it exhibited two decomposition temperature ranges (710-900oC and 900-1130oC). The final product consisted of a mixture of gadolinium tungstate of different composition. This suggests the decomposition scheme of polyphase products


PRELIMINARY EVIDENCE FOR A SECOND ~525-545 Ma OLD EVENT OF GRANULITE FACIES METAMORPHISM IN THE MOZAMBIQUE BELT OF TANZANIA AND ITS IMPLICATIONS FOR A TWO-STAGE MODEL FOR GONDWANA ASSEMBLY


MAH Maboko
Department of Geology, University of Dar Es Salaam
P.O. Box 35052 Dar es Salaam, Tanzania


ABSTRACT
Garnets from two samples of the Kitumbi granulites in the Mozambique Belt of north eastern Tanzania yield Sm-Nd ages of 525±15 Ma and 545±15 Ma. At the 95% confidence level, these ages are younger than the 576 ±15 to 634±16 Ma (Mean 606±12 Ma) ages previously reported from the more extensive Eastern Granulites. The Kitumbi garnets are therefore interpreted as dating cooling from a granulite facies event that is distinctly younger than the 630-700 Ma event that produced the Eastern Granulites. Unlike the Eastern Granulites, the Kitumbi rocks occur as small enclaves not separated from the surrounding amphibolite facies gneisses by any obvious structural discontinuity, lack the continental margin geochemical signatures that characterise the Eastern Granulites and yield late Archean depleted mantle crustal formation ages, similar to those obtained from the surrounding gneisses. These characteristics suggest that, unlike the Eastern Granulites that are isotopically exotic slices emplaced onto the surrounding amphibolite facies gneisses, the Kitumbi granulites are products of ~550 Ma old in situ granulite facies metamorphism of the surrounding country rocks. The existence of a regional granulite facies event at ~530-550 Ma offers a way of reconciling the palaeomagnetic and petrological/geochronological evidence for Gondwana assembly. Thus, as has been previously proposed by Meert et al. (1995), the 630-700 Ma old event that produced the Eastern Granulites may record regional crustal thickening arising out of collision of India, Madagascar, parts of Easten Antarctica and the Kalahari craton (IMSLEK terranes) with the Congo craton and the Arabian Nubian Shield (ANS). The younger granulite event recorded in the Kitumbi area could then mark a younger collision between Australo-Antarctica and the combined IMSLEK-Congo-ANS collage marking the final assembly of Gondwana.

COMPOSITION AND ANAEROBIC DIGESTION OF SINGLE AND COMBINED ORGANIC FRACTIONS OF MUNICIPAL SOLID WASTE OF DAR ES SALAAM

AK Kivaisi and J Mukisa
Applied Microbiology Unit, University of Dar es Salaam,
P.O. Box 35060, Dar es Salaam, Tanzania

ABSTRACT
The composition of major categories of municipal solid waste (MSW) of Dar es salaam city was determined. Food remains and vegetable matter constituted 80-90% of the categories. Organic fractions of the individual categories contained 18-20 % total solid (TS), 30-50 % (dry weight) total fibre and 1-1.3 % nitrogen. The assorted organic fractions were tested for anaerobic conversion into biogas at 55°C in batch cultures for 14 days with a mixed population of microorganisms. At a substrate concentration of 6-8 g volatile solids per litre fermenter volume (g VS l-1 FV) individual fractions were degraded by 51-75% and gave methane yields in the range of 390-492 ml per gram VS added. Combining individual fractions with chicken manure at a ratio of 1:1 (TS) increased the N-content of the fractions by 16-133% and the VS content of the fermenting substrate doubled. Overall methane production by the combined fractions increased by 8-20% over that measured for the individual fraction incubations, but methane yields decreased by 30-50%. The mixed waste category constituting a substrate concentration of 6 g VS l-1 FV was degraded by 65% and gave a yield of 428 ml CH4 per gram VS added. This study concludes that individual fractions of MSW of Dar es salaam city are suitable as feedstocks for biogas digesters. The decreased overall conversion of the fractions when combined with chicken manure was attributed to high ash content of the manure. 

INFLUENCE OF ENDOCRINE ACTIVITY ON LARVAL DEVELOPMENT IN BUSSEOLA FUSCA (FULLER)(LEPIDOPTERA:NOCTUIDAE)

MA Njau
Department of Zoology and Marine Biology, University of Dar es Salaam 
P.O. Box 35064. Dar es Salaam, Tanzania

ABSTRACT
The present study investigated the role of juvenile and moulting hormones in development of Busseola fusca. Morphometric measurements were used to distinguish differences in endocrine activity between non-diapause and diapause development with regard to the prothoracic glands and the corpora allata. The corpora allata of non-diapause larvae were similar in size to those of diapause larvae. The critical period for the prothoracic glands to produce the required titer of ecdysone for further development was by the third day after ecdysis to the last larval instar. Juvenile hormone extracts from haemolymph of Busseola fusca larvae in non-diapause and diapause development had morphometric effects on last instar nymphs of Dysdercus cingulatus. The extent of juvenilization of nymphs by these extracts was a measure of relative titer of juvenile hormone present. Extracts of JH from the fifth instar larvae of Busseola fusca and larvae in early diapause gave higher juvenilizing scores than JH from non-diapause sixth instar larvae.