Research Repository :: Browsing by Author "Machiwa, John F."

Browsing by Author "Machiwa, John F."

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Anthropogenic Pollution in the Dar es Salaam Harbour Area, Tanzania.
(Elsevier, 1992-11) Machiwa, John F.
Man-made pollutants, namely, petroleum hydrocarbons, polychlorinated biphenyls (PCBs), and heavy metals as well as microbial pollution in the sediments of the harbour channel have been evaluated. Petroleum hydrocarbons, PCBs and heavy metals (Fe, Pb, Cu, and Zn) are at elevated levels in the port area used for loading and unloading activities. The concentration of the chemicals decreases further offshore, with the exception of cadmium which, surprisingly, is enriched in the sediments at the ship outer anchorage zone. The concentration-depth profile of the sediment core samples show that in general metals are uniformly distributed with depth in the sediment. The between station variation of Mn, Cr and Ni is strongly influenced by grain size differences. Total and faecal coliform bacteria are few in the port area but are extremely abundant at the fish landing beach and close to the sewer outfall
Assessment of Heavy Metal Pollution in Sediment and Polychaete Worms from the Mzinga Creek and Ras Dege Mangrove Ecosystems, Dar es Salaam, Tanzania
(University of Dar Es Salaam, 2008) Mtanga, A.; Machiwa, John F.
Metal pollution in the Mzinga creek mangrove stand was assessed and compared with a relatively pristine mangrove forest at Ras Dege in Dar es Salaam. The concentrations of cadmium, chromium, copper, lead and zinc in sediment and polychaete worms (Capitella sp.) were analyzed by ICP-AES and mercury was analyzed by a semi-automatic analyzer. Concentrations of most of the metals analyzed were higher in samples from Mzinga creek than from Ras Dege. Sediment samples from the Mzinga creek were enriched with Cu (EF = 7.4), Hg (EF = 5.3) and Cr (EF = 3.3) relative to sediment samples from Ras Dege, which were mostly at natural background levels. Polychaete worm samples from the Mzinga creek also accumulated high amounts of metals when compared to samples from Ras Dege. The data show perturbation of the Mzinga creek from human activities in the catchment.
Coastal Marine Pollution in Dar es Salaam (Tanzania) relative to Recommended Environmental Quality Targets for the Western Indian Ocean
(University of Dar Es Salaam, 2010) Machiwa, John F.
Pollution surveys were undertaken during 2007 and 2008 in the coastal marine environment of Dar es Salaam and the remote Ras Dege Creek. The objective was to determine the levels of microbial contamination, heavy metals and persistent organic pollutants and compare these with the recommended environmental quality targets (EQTs) for the West Indian Ocean (WIO). Levels of microbial pollution in urban coastal waters off Dar es Salaam were excessive, indicating that water within the port channel was not safe for contact recreation. Seafood from areas adjacent to Msimbazi Creek and the Ocean Road sewer outfall was unfit for human consumption. Conversely, the water quality of Ras Dege Creek was excellent for contact recreation as well as for the collection of seafood. Concentrations of heavy metals, even in the coastal marine environment off Dar es Salaam, were not significantly high compared with the recommended EQTs. Although some persistent organic pollutants exceeded the recommended EQTs in sediment and oysters along the coast of Dar es Salaam, this was not the case at Ras Dege. The lack of sufficient wastewater treatment facilities is the main cause of current levels of some pollution in the coastal marine environment off Dar es Salaam. The implementation of industrial and municipal wastewater management would greatly improve this situation. The results show that the proposed EQTs would constitute appropriate standards for coastal marine water quality in Tanzania.
Concentrations of Metals in River Sediment and Wetland Vegetations in Mining, Lake Victoria basin, Tanzania
(University of Dar Es Salaam, 2003) Machiwa, John F.
Levels of metals were determined in river sediment, rice and sugarcane juice from Lake Victoria basin where small-scale gold processing activities are carried out to assess levels of contamination. Concentrations of metals in river sediments were generally high in areas that were closest to gold ore processing sites. For instance, mercury was highest (36.3 ±12.8 mg/g dw) in river sediments of Tigiti River in Mugumu District. Other heavy metals (Cd, Pb, Zn and Cu) had highest concentrations (2.20±0.71, 208±19.3, 412±20.1 and 132.7±11.9mg/g dw, respectively) in sediment samples from Kagota. The concentration of arsenic was highest (985.0±67.2 mg/g dw) in Mugusu River sediment. Mercury concentration in rice was highest (378.5±15.1mg/kg dw) in samples from Lwamgasa wetland and lowest (47.9±2.9 mg/kg dw) in samples from Saragurwa wetland. Cadmium concentrations in rice ranged from 2.3-5.5mg/kg dw, Zn and Cu ranged from 16340-27280mg/kg dw and 1150-2240mg/kg respectively. Arsenic was not detected in any rice sample. Lead was only detected in rice from Sengerema (150±12mg/kg dw), in a wetland that is close to the main road. Mercury concentrations in sugarcane juice were below the limit of detection (0.01mg/l) in all samples even those that were harvested closest to the gold ore-washing site at Samina. It is concluded that small-scale gold mining activities contaminate watercourses close to ore washing sites.
d13C Signatures of Flora, Macrofauna and Sediment of a Mangrove Forest Partly Affected by Sewage Wastes
(2004) Machiwa, John F.
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.
Developing Human Capital for Successful Implementation of International Marine Scientific Research Projects
(University of Wollongong, 2013) Morrison, R. J.; Zhang, J.; Urban, E. R.; Hall, J.; Ittekkot, V.; Avril, B.; Hu, L.; Hong, G. H.; Kidwai, S.; Lange, C. B.; Lobanov, V.; Machiwa, John F.; San Diego-Mcglone, M. L.; Oguz, T.; Plumley, F. G.; Yeemin, T.; Zhu, W.; Zuo, F.
The oceans play a crucial role in the global environment and the sustainability of human populations, because of their involvement in climate regulation and provision of living and non-living resources to humans. Maintenance of healthy oceans in an era of increasing human pressure requires a high-level understanding of the processes occurring in the marine environment and the impacts of anthropogenic activities. Effective protection and sustainable resource management must be based, in part, on knowledge derived from successful research. Current marine research activities are being limited by a need for high-quality researchers capable of addressing critical issues in broad multidisciplinary research activities. This is particularly true for developing countries which will require the building of capacity for marine scientific research. This paper reviews the current activities aimed at increasing marine research capacity in developing and emerging countries and analyses the challenges faced, including: appropriate alignment of the research goals and societal and policy-relevant needs; training in multidisciplinary research; increasing capacity for overall synthesis of scientific data; building the capacity of technical staff; keeping highly qualified personnel in marine scientific research roles; cross-cultural issues in training; minimising duplication in training activities; improving linkages among human capital, project resources and infrastructure. Potential solutions to these challenges are provided, along with some priorities for action aimed at improving the overall research effort.
Distribution and Remineralization of Organic Carbon in Sediments of a Mangrove Stand Partly Contaminated with Sewage Waste
(Springer, 1998-12-01) Machiwa, John F.
The distribution of soil organic carbon in a mangrove forest partly contaminated with raw sewage shows that a high proportion of the carbon in the landward zones of the forest was organic. Relative content of inorganic carbon increased seawards. Carbonate from the shells of gastropods, oysters, and corals contribute to the inorganic carbon pool. The vertical profiles of organic carbon showed a general surface enrichment and subsurface depletion. An extremely high organic carbon content up to 19% of sediment (dry weight) was found at the sewage dump site. Peat formation was not evident and the organic carbon content decreased with depth of burial in the sediment. The interstitial water at the terrestrial mangrove fringe with sewage waste was relatively more acidic (pH 4-5) and strongly reducing (Eh - 300 mV). The pH in the terrestrial fringe that had no sewage influence was close to neutral values (pH > 6). There was no significant difference between the rates of organic matter remineralization in the forest zones. Relative values, however, indicate that mineralization was slowest in sewage-contaminated areas compared to areas without exposure to sewage. The rate of remineralization was high in the frequently inundated mangrove areas.
Distribution of heavy metals in sediments of Mwanza Gulf of Lake Victoria, Tanzania
(Elsevier, 2003-02) Kishe, M. A.; Machiwa, John F.
Sediment samples were analyzed for Cd, Cr, Cu, Pb, Hg and Zn by AAS. The highest concentrations (ppm) for Cu (26.1F4.8), Hg (0.2F0.05), Pb (30.7F5.6) and Zn (45.4F13.1) were found at approximately 25 m from the shoreline. Generally, heavy metals concentration in the sediment decreased with increasing distance from the shoreline except for Cd and Cr whose highest concentrations were found at approximately 2000 m from the shoreline. The data also indicated that sediment samples which were collected at the shores within the urban area of Mwanza showed elevated levels of Pb (54.6F11.1 ppm) and Zn (83.7F21.5 ppm). However, the highest concentrations of Cd (7.0F2.1 ppm), Cr (12. 9F1.0 ppm) and Hg (2.8F0.8 ppm) were recorded at sampling stations which were adjacent to river mouths.
Effect of an Impoundment on Nutrient Dynamics in the Kihansi River, Tanzania
(Taylor & Francis Group, 2008) Ideva, R. J.; Machiwa, John F.; Schiemer, F.; Hein, T.
The impact of the Kihansi Dam on electrical conductivity, pH, temperature and dissolved oxygen in the Kihansi River was assessed in 2005 after 85% of the original river flow had been diverted to the Lower Kihansi power plant. The results are compared with the data obtained in 1995 before the dam was constructed. Primary production and nitrogen and phosphorus concentrations from sites upstream and downstream of the dam as well as in the reservoir were compared. Phosphorus fractions were determined in the reservoir's sediment. Electrical conductivity and pH values were higher in 2005 than in 1995, whereas oxygen concentrations were lower. Primary production, nitrogen and phosphorus concentrations were lower at stations downstream of the dam than at upstream stations. High fractions of iron- and manganese-bound phosphorus in the reservoir sediment suggest a potential for phosphorus retention. Concentrations of nitrogen and phosphorus along the Kihansi River were higher during the dry season than in the wet season. These results contribute to the documented baseline data on environmental changes in tropical river systems after flow diversion and reservoir development.
An Empirical Model of the Fate of Organic Carbon in a Mangrove Forest Partly Affected by Anthropogenic Activity
(2002-01) Machiwa, John F.; Hallberg, Rolf O.
A model of biogeochemical and hydrological processes that drive organic carbon dynamics of a mangrove ecosystem has been developed. Tidal regime parameters as well as biological factors related to macrofauna and microbiota are described within the model. The model includes three sub-models, each representing a major form of organic carbon in the mangrove ecosystem; litter organic carbon, particulate organic carbon and dissolved organic carbon (DOC). Results from the model reveal that discharge of DOC to the adjacent ocean may be one of the dominant outputs of a mangrove forest. The model confirms the observed data that DOC accounts for 80% of total organic carbon export. In order to balance the standing crop of DOC in the marine fringe zone, the model suggested that 40% is removed in this zone by microorganisms as well as resident and tidal migrant fauna.
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.
Flora and Crabs in a Mangrove Forest Partly Distorted by Human Activities, Zanzibar.
(Elsevier, 1995-12) Machiwa, John F.; Hallberg, Rolf O.
A preliminary study on flora and fauna in a disturbed mangrove ecosystem is presented. The zonation of mangrove flora in the forest is clearly displayed by two dominant species, Avicennia marina and Sonneratia alba. A. marina forms an almost pure stand at the terrestrial edge of the forest, but the species is ubiquitous in the area. S. alba almost exclusively occupies the marine fringe of the forest.
Heavy Metal Contamination of Mangrove Sediments and the Associated Biota in Dar es Salaam, Tanzania
(University of Dar Es Salaam, 2004-10) Mremi, S. D.; Machiwa, John F.
Mangrove wetlands are efficient in trapping pollutants that may have detrimental effects on mangrove dependent food chains. Mangrove ecosystems that are within urban areas are likely to suffer more from chemical pollution than those in rural areas. Heavy metals in mangrove plant parts, sediments and crabs from mbweni, msimbazi and mtoni mangrove ecosystems in Dar es salaam were analysed using an atomic absorption spectrophotometer, in order to assess the impact of heavy metal pollution on mangrove biota. Sediment samples from msimbazi and mtoni mangrove areas which are located within the city, had higher levels of pb, zn and cu than those from mbweni mangrove stand, which is far from the city centre. For instance, the concentration of pb was 31.6 ± 9.6 µgg-1 dw at msimbazi, 17.9 ± 10.7 µgg-1 dw at mtoni and 13.3 ± 3.5 µgg-1 dw at mbweni mangrove area. Crabs generally contained higher concentrations of heavy metals (pb, zn and cu) on dry weight basis compared with sediment and mangrove plant parts. Copper enrichment in crabs, for example, was more than six times compared with the concentration in sediment samples from msimbazi mangrove mangrove forest. Of the seven heavy metals (pb, zn, cu, co, ni, cr and v), only pb, zn and cu were found to be of anthropogenic origin. Overall, the mangroves and associated biota in mangrove forests, that are within the city, had higher levels of heavy metals compared with mangrove forests growing away from the city.
Heavy Metal Levels in Paddy Soils and Rice (Oryza Sativa (L)) From Wetlands of Lake Victoria Basin, Tanzania
(University of Dar Es Salaam, 2010) Machiwa, John F.
A survey of paddy fields in Lake Victoria Basin (LVB) wetlands was conducted at a wider scale in different locations including closer to mining and within urbanized areas in Tanzania. The objective of the study was mainly to assess the present situation with regard to levels of heavy metals in O. sativa grains harvested locally as well as to set the baseline levels of some heavy metals in paddy fields. The results showed that the levels of Cadmium, Chromium, Copper, Lead, Zinc and total Mercury in brown rice are generally within the acceptable levels for human food. However, higher concentration of Hg was found in the husks, suggesting the significance of atmospheric dispersal of Hg in the basin. It is also worthwhile noting that all the sampled paddy fields in LVB have heavy metal concentrations within limits for production of safe rice for human consumption.
Heavy Metal Pollution Levels in Water and Oysters, Saccostrea Cucullata, from Mzinga Creek and Ras Dege Mangrove Ecosystems, Tanzania
(Taylor & Francis Group, 2007-11) Mtanga, Augustina; Machiwa, John F.
Heavy metal (cadmium, chromium, copper, mercury, lead and zinc) concentrations in mangrove forests were investigated in water, suspended particulate matter (SPM) and oyster samples from the Mzinga Creek and Ras Dege mangrove stands, Tanzania, using Inductively Coupled Plasma–Atomic Emission Spectroscopy. With the exception of Zn, the concentrations of dissolved metals were generally less than 1μg l–1 in all samples. Higher concentrations of metals were recorded in SPM in samples from the Mzinga Creek mangrove forest, on ebb tides during the rainy season. Concentrations of Cd in SPM ranged from 33.9–85.5μg g–1 dw and, for Cr, from 23.9–138.1μg g–1 dw. The concentration of Pb ranged from 56.5–114.0μg g–1 dw and the concentration of Zn in SPM from Mzinga Creek was 35 times higher than that of Ras Dege, with concentration ranges between 229.8 and 1 427.3μg g–1 dw. In Ras Dege, concentrations of Cd, Cr, Cu and Pb in SPM were generally lower than those of Mzinga Creek. Metal concentrations in oysters were of an order of magnitude higher in Mzinga Creek than in Ras Dege. These results are indicative of the contributions of heavy metal pollution from several anthropogenic sources, such as industrial and agricultural activities, in the Mtoni Creek catchment. Dar es Salaam seaport is a potential source of heavy metals to the Mzinga Creek mangrove stand. In comparison with the less-impacted Ras Dege mangrove stand, Mzinga Creek's environmental condition calls for urgent management intervention.
Heavy Metals and Organic Pollutants in Sediments of Dar es Salaam Harbour Prior to Dredging in 1999
(2004) Machiwa, John F.
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.
Influence of Land Use Patterns on some Limnological Characteristics in the South-Eastern Part of Lake Victoria, Tanzania
(Taylor & Francis Group, 2011-09-08) Shayoa, Salome D.; Lugomela, Charles; Machiwa, John F.
To investigate the influence of human activities on limnological characteristics of Lake Victoria, we analyzed inorganic nutrient concentrations, phytoplankton diversity and biomass at three locations with different land use patterns: Mwanza (urban/industrial), Magu (agricultural) and Kayenze (sparsely populated). Mwanza had significantly higher ammonia concentration compared to Kayenze and Magu. At the shoreline stations, significantly higher nitrate concentration was observed at Mwanza compared to Kayenze and Magu. Similarly, Mwanza had significantly higher concentrations of soluble reactive phosphorous in the shoreline stations compared to Magu and Kayenze, but not in the open waters stations. Shoreline stations also showed significant differences in phytoplankton diversity among sites. The shoreline station at Mwanza also showed significantly higher levels of Chl. a compared to those at Magu and Kayenze. However, in the open water stations Chl. a concentrations did not differ significantly among sites. The results suggested that urban pollution in Mwanza and agricultural activities in River Simiyu catchment strongly influence the limnology of Lake Victoria and that the nearshore waters, which are the receiving points, were highly impacted compared to the waters outside bays. Thus, proper urban waste management and sustainable land management practices are critical for reducing point and non-point sources of pollution into Lake Victoria.
The Influence of Land-Use Patterns in the Ruvu River Watershed on Water Quality in the River System
(Elsevier, 2004-10) Ngoye, Elizabeth; Machiwa, John F.
This work assessed the impacts of land-use patterns in the Ruvu river basin on water quality in the river system. Seasonal changes in water quality parameters were also investigated. Ten river water-sampling stations were selected and samples were collected and analysed according to standard analytical procedures. The results showed that physico-chemical parameters of river water ranged as follows: pH, from 6.95 ± 0.09 to 8.07 ± 0.23; temperature, from 14.0 ± 0.06 to 31.1 ± 0.4 °C; EC, from 39.8 ± 0.8 to 48,734 306 μs/cm; TDS, from 19.9 ± 0.4 to 24,367 ± 152.9 mg/l; turbidity, from 3.0 ± 0.6 to 840 ± 69.3 NTU and DO, from 6.8 ± 0.02 to 16.78 mg/l. The ranges for nutrient concentrations were NO3–N, from 0.006 ± 0.0003 to 0.62 ± 0.3 mg/l; NH4–N, from 0.34 ± 0.17 to 16.2 ± 0.5 mg/l; PO4–P, from 0.009 ± 0.001 to 1.75 ± 0.2 mg/l and TP, from 0.02 ± 0.003 to 3.56 ± 0.38 mg/l. Generally, water samples from stations with forested catchments had high levels of DO and low levels of NH4–N and NO3–N compared to those from farmland, industrial, residential and market places. There were clear seasonal variations showing an increase in the concentrations of nutrients during rainy season. The results show impairment of the water quality of the river by anthropogenic activities in the catchment. Water pollution prevention strategies to ensure prevention of pollution and protection of water resources in the Ruvu river watershed are recommended.
Investigating the distribution and fate of Al, Cd, Cr, Cu, Mn, Ni, Pb and Zn in sewage-impacted mangrove-fringed creeks of Kenya, Tanzania and Mozambique
(Springer Berlin Heidelberg, 2015-12) Kamau, JN; Kuschk, P; Machiwa, John F.; Macia, A; Mothes, S; Mwangi, S; Munga, D; Kappelmeyer, U
Purpose Coastal towns in the developing world are faced with the challenge of wastewater treatment. Most of the domestic wastewater generated in these urban areas is discharged raw into the surrounding mangrove forest. The local communities living near mangrove-fringed creeks are artisanal fishers and rely on fish as a source of protein. It is therefore important to determine the impact of sewage input on metal mobility/bioavailability in these mangrove systems. Materials and methods The fate of heavy metals was investigated in peri-urban mangrove systems of Kenya, Tanzania and Mozambique. Enrichment factors (EF) and pollution factors (PF) were applied to investigate the pollution status of selected metals in sewage-impacted creeks of the three countries. The spatial distribution patterns of metals in sediments and in the water column were determined. A sewage factor (SF) index was derived to determine the impact of sewage input on the water column. Results and discussion Data obtained from sediment analysis revealed that Cd was highly depleted (EF 0.1) at Costa do Sol in Mozambique, inferring that it is highly labile under the prevailing onsite physicochemical parameters. Comparatively, Cr was more enriched in Mozambique sediments than in Kenya and Tanzania. In Tanzania; Zn showed the highest pollution levels (PF, 3.20), with reference to Ras Dege. While in Kenya, zinc was the most polluting metal in all of the sediment segments at Tudor Creek with reference to Gazi Creek. There was a conservative mixing of sediment/particulate-hosted heavy metals at Tudor and Ras Dege. This behaviour was observed for all the metals analysed. At Mtoni, however, the conservative behaviour was only pronounced for Pb and Zn, while for all three sites in Mozambique, metals were distributed evenly across the creeks indicating sinking tendencies. Sewage discharge influenced the concentration of dissolved Cr and Pb at Fort Jesus station during both flood and ebb tide. Conclusions Changes in physicochemical parameters strongly influence the fate of sediment-hosted Cd as observed at Costa do Sol. The preferential association of Cd onto carbonates enhances Cd enrichment in sediments rich in carbonates. Input of domestic sewage contributes to dissolved Al loading, which is attributed to the use of alumina in fresh water treatment plants.
Lateral Fluxes of Organic Carbon in a Mangrove Forest Partly Contaminated with Sewage Wastes
(1999-06) Machiwa, John F.
Lateral fluxes of macrodetritus, particulate matter and dissolved organic carbon were determined. Samples were collected monthly at the mangrove forest–inshore water boundary and within the forest. Floating macrodetritus (mainly mangrove leaves) was collected by a net (2 mm mesh size). Dissolved and particulate matter were separated by filtration (0.45 µm filter) and centrifugation. Dissolved and particulate carbon were determined by a total organic carbon analyser (SHIMADZU model TOC-5000). There was a significant export of mangrove litter to the adjacent marine environment during spring tides. Rates of import and export of particulate matter in the forest were not statistically different. Trans-location of material within the forest was clearly demonstrated. A relatively high export of macrodetritus was recorded at the marine fringe (mainly colonised by Sonneratia alba). There was low export of litter in the terrestrial fringe zone, a mono-specific stand occupied by Avicennia marina (Forsk) Vierh. Net organic carbon export from the entire forest was 79 × 106gCy−1, dissolved organic carbon accounted for about 78% of the total export.

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