African Journals Online
Tanzania Journal of Science

Volume 27A (Special Issue) 2001
CONTENTS

The emplacement age of gabbroic rocks and associated granitoids of the Liganga-Msanyo complex, south eastern Tanzania.

MAH Maboko

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

ABSTRACT

The Msanyo Gabbro and the associated Mdando granitoids, which intrude Paleoproterozoic high-grade metamorphic rocks of the Ubendian Belt in southern Tanzania, yield imprecise Sm-Nd whole rock isochron ages of 1608±134 Ma (ε (Nd) = 2.1) and 1642±100 Ma (ε (Nd) = 1.6), respectively. These ages are indistinguishable at the 95% confidence level, indicating that the two rock suites were intruded at the same time. A more precise estimate of the time of emplacement is provided by a 5-point mineral isochron age of 1505±42 obtained from one of the gabbro samples. Calculated initial ε (Nd) values and mean crustal residence ages are similar for both rock suites and range from –0.7 to 1.5 and 1.7 to 1.9 Ga. Respectively. Initial Sr isotope ratios lie between 0.7032 and 0.7039 and these values are similar to those obtained in the mantle and the lower continental crust. The rather evolved Nd isotope systematics, combined with the relatively non-radiogenic Sr isotopic signature, suggest that both suites cystallised from mantle-derived magma that had assimilated a significant amount of lower continental crustal material. Subsequent to their emplacement, the rocks experienced localised shearing and sericitisation during the Ukingan tectonic event. A Rb-Sr plagioclase-whole rock age dates this event at 1137±50 Ma.

Assessment of heavy metal pollution in the Lupa gold field, SW Tanzania.

SR Mnali

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

ABSTRACT

The concentrations of AS, Cd, Cr, Cu, Hg and Pb were determined in water, stream sediments, soil, and mine tailings from Lupa Gold Field (LGF), SW Tanzania, in order to assess their pollution levels. As, Cd and Cr were determined by automated Graphite Furnace Absorption Spectrophotometry. Cu and Pb were analysed by Air-Acetylene Flame, while Hg was analysed by Cold Vapour Atomic Absorption Spectrophotometry. The mean concentrations obtained were: As: 0.44 ppb (water), 1.2 ppm (sediments), 0.44 ppm (soil) and 5.2 ppm (tailings); Cd: 0.03 ppb (water), 0.03 ppm (sediments), 0.03 ppm (soil) and 0.50 ppm (tailings); Cr: 1.4 ppb (water), 70 ppm (stream sediments), 250 ppm (soil) and 270 ppm (tailings); Cu: 30 ppb (water), 68 ppm (sediments), 66 ppm (soil) and 455 ppm (tailings); Hg: 0.25 ppb (water), 1.1 ppm (sediments), 0.10 ppm (soil) and 8.70 ppm (tailings) and Pb: 0.50 ppb (water), 85 ppm (sediments), 22 ppm (soil) and 275 ppm (tailings). Leaching of As-based mineral flotation reagents as well as the decomposition of accessory As minerals such as arsenopyrite (FeAsS), enargite (Cu₃AsS₄) and tennantite (Cu₁₂As₄S₁₃) most likely contributed to some high As concentrations in the mine tailings. The low Cd content in all samples reflects the low content of sphalerite (in which Cd replaces Zn) typical of the LGF ores. Cromium was low in water, most likely because of its low mobility; it was high in soils and tailings derived from mafic-ultramafic rocks. High Cu levels in tailings came from dissolution of chalcopyrite and bornite. Neutral to alkaline pH conditions (6.5-8.5) of water was most likely responsible for its low Cu levels. Amalgamation of Au concentrate likely introduced Hg into the environment. Dissolution of galena and anglesite was likely the source of Pb into the soils, sediments and tailings. The range of concentrations of the six heavy metals recorded in the Lupa gold field is of great concern to human health.

Tectonic setting and uplift analysis of the Pangani Rift Basin in Northern Tanzania using apatite fission track thermochronology

EI Mbede

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

ABSTRACT

Thirty four new Apatite Fission Track (AFT) ages and 32 track length distributions from samples of basement rocks flanking the Pangani rift, East African Rift System (EARS) are presented, in an attempt to elucidate the uplift and erosion of the rift flanks. The ages fall in the range of 207±15 to 48±4 Ma, spanning from Early Jurassic to Early Tertiary. These ages are much younger than the last termal event in the Mozambique belt that form the basement complex and are interpreted to represent the most recent tectonic events. Track length (TL) distributions suggest that uplift and erosion of the rift flanks are related to three different tectonic events, which are also recorded by the sedimentary units within the adjacent coastal basins. These include the Triassic/Early Jurassic, Late Cretaceous and Early Tertiary tectonic events. Erosion and isostatic rebound have modified the tectonically induced topographic patterns and the highly elevated plateaus flanking the Pangani rift represent an erosional surface referred to as the “Gondwana surface” of eastern and central Africa. The present AFT data suggest that initial exhumation of the “Gondwana surface” from the temperatures above 110º to temperatures less than 60ºC, in this area, took place during Early Jurassic times, but the final sub-aerial exposure of the surface did not take place until Early Tertiary.

Sources and diagenetic alteration of organic matter in coastal waters at the vicinity of Dar es Salaam, Tanzania

ANN Muzuka

Institute of Marine Sciences, University of Dar es Salaam, P.O. Box 668, Zanzibar, Tanzania

ABSTRACT

The stable isotope compositions of organic carbon (OC) and nitrogen, contents of OC and nitrogen, and C/N ratios for four short cores, which were recovered from Msansani Bay (WO 57), off Msimbazi River (WO 76) and Dar es Salaam harbour (WO 62 and WO 74), are used to document temporal variation in the sources and diagenetic alteration of organic matter (OM). The δ¹⁵N and δ¹³C values at sites WO 57, WO 62 and WO 74 show a trend of down-core decrease to the base of the core, and such a down-core trend could be related to diagenetic loss of compounds enriched in ¹³C and ¹⁵N. At site WO 76, the δ¹³C values show two zones that are depleted in ¹³C. These two zones correspond to black-greasy layers that were observed during sampling, and low δ¹³C values probably is an indication that the material was derived from the continent. Furthermore, these two zones have elevated values of OC, nitrogen and C/N ratios. The stable isotopes of OC and nitrogen show inter-sites differences with enrichment in ¹⁵N in the following order: WO 57 < WO 74 < WO 62 < WO 76. A similar inter-core difference is observable for the 13C, but the enrichment show a reversed order. The inter-site differences in 13C and ¹⁵N could be related to the sources of OM. In the Msansani Bay the material is derived from seagrasses while in the Dar es Salaam harbour and Msimbazi micro-bay, large proportion is derived from the continent. Other parameters of OC, nitrogen and C/N ratios for these three sites show a slight down-core decrease to the base of the core, probably the result of diagenetic alteration of OM. Highest contents of OC and nitrogen are observable at site WO 62 owning to preferential preservation of OM due to high input of more refactory material derived from the continent and lack of tidal flushing.

The occurrence of digenean larvae in freshwater snails at Mbezi-Timboni pond, Dar es Salaam

ESP Kigadye

Department of Zoology, The Open University of Tanzania, P.O. Box 23409, Dar es Salaam, Tanzania

G Nkwengulila

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

ABSTRACT:

The abundance of digenean larvae in snails at a pond in Mbezi-Temboni, Dar es Salaam, was investigated from July 1996 to June 1997. A total of 2,112 snails belonging to three species, Bulinus globosus Morelet 1866, Bulinus forskalii Ehrenberg 1869, and Melanoides tuberculata Müller 1774 were examined, and 28 (1.3%) were found infected by four species of digenean trematodes. Trematodes were recovered only from Bulinus species; none of the examined M. tuberculata was infected. B. globosus  was infected by Schistosoma haematobium Bilharz 1852 (1.14%), unidentified furcocercous cercariae (0.4%), and echinostome cercariae (0.76%). B. forskalii was infected by echinostome cercariae (0.25%) only, Generally, prevalence of digenean larvae in their host snails was very low and varied with the seasons. Variation of prevalence with the seasons was probably influenced by factors such as rainfall, population dynamics of host, and temporal availability of definitive hosts. Furthermore, S. haematobium and echinostome cercariae from B. globosus occurred alternately but not concurrently, suggesting a possible presence of intramolluscan competition.

Experimental spat collecting of the edible oyster, Saccostrea cucullata born (Bivalvia) in the Kunduchi Creek, Dar es Salaam

YD Mgaya

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

ABSTRACT

A one year study was carried out at Kunduchi Creek, Dar es Salaam, to determine spat settlement using the three different substrates (clutches): coconut shells, asbestos and cockle shells, set at three different depths, 0.5 m, 1 m, and 1.5 m. The experiment was set up at three different sites within the creek. There were no significant differences among treatments (sites, depths, clutches). However, spat settlement exhibited seasonal differences, with peak spatfall recorded during the long rains (April to May). There were significant differences in the number of spat between the upper and lower surfaces of the substrates, with more spat preferring the underside. It was concluded that the Kunduchi Creek is a potential site for oyster farming. However, since the area is heavily used by artisanal fisherfolk, any future plans to establish mariculture operations would have to take into consideration potential conflicts with other user groups.

Combined chemical and biological treatment of recalcitrant industrial effluents: a case study on kraft pulp wastewater

GYS Mtui

Department of Botany and Applied Microbiology, University of Dar es Salaam, P.O. Box 35060, Dar es Salaam, Tanzania

ABSTRACT

The chemical degradation of lignin-rich kraft pulp wastewater was carried out by ozonation process flowed by biological treatment using activated sludge. The effects of pH on the degradation of lignin and the production of organic acids were examined experimentally in the ozonolysis of wastewater. The strong alkaline condition enhanced not only the degradation of lignin but also the production of organic acids. The maximum value of BOD₅/COD obtained after 12 hours of ozonation was 0.41, indicating that ozone treatment improved the biodegradability of the kraft pulp wastewater. The dynamic behaviours of microbial growth and substrate consumption were investigated in the biodegradation of organic acids using activated sludge. Maleic acid and oxalic acid in the ozonized wastewater were degraded completely by the activated sludge in shake-flasks and bench-scale aerated bioreactor experiments. The immobilized activated sludge culture using polyurethane foam (PUF) was most effective in degrading organic acids in continuous culture condition at an optimum hydraulic retention time (HRT) of 14 hours. The study confirmed that consecutive treatments by ozone and activated sludge are effective methods to treat industrial effluents containing recalcitrant environmental pollutants such as kraft pulp wastewater.