Browsing by Author "Yohana, Lawi"

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    An investigation on the effects of edaphic and anthropogenic factors on woody plant species distribution in pande game reserve, Dar es Salaam region
    (University of Dar es Salaam, 2004) Yohana, Lawi
    The relationship between environmental variables and woody plant species distribution in Pande Game reserve was studied using multivariate gradient analysis. Vegetation data were collected in 20 established releves using the stratified random sampling method. For each releve established environmental data on edaphic factors and anthropogenic disturbances were also collected. The plant species were classified using a FORTRAN computer program TWINSPAN and detrended correspondence analysis (DCA) in which three major plant communities were identified. Canonical correspondence analysis (CCA) revealed significant relationship between environmental factors and the distribution of woody plant species in which, phosphorus (p < 0.015). disturbance (p < 0.01). clay (p< 0.035), and soil moisture (p < 0.01) were the most significant factors at the respective levels. The Shannon - Weaver species diversity index was used to find the mean a- diversity of the woody plant species in the three communities identified. The Moderately disturbed community had the highest mean a-diversity (1.5007 ± 0.1272). followed by the undisturbed community (1.4787±0.241) and the highly disturbed community had the lowest mean value (0.7282 ± 0.4230). The Turkey - Kramer Multiple Comparison test showed that, there were significant differences in a-diversity between the highly disturbed forest community and the moderately disturbed forest community (p < 0.05). Furthermore, there was a very significant difference in a-diversity between the undisturbed forest and the highly disturbed forest (p < 0.01). But there was no significant difference between the a- diversity indices of the undisturbed community and the moderately disturbed community despite the fact that the index of the moderately disturbed community was slightly higher. Thus, moderate anthropogenic disturbances increased species diversity in the study area but severe disturbance decreased the species diversity of the woody plants that constitute typical forest vegetation.
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    Potential re-use of treated wastewater from a horizontal subsurface flow constructed wetland for aquaculture production: modeling of nitrogen dynamics and removal in aquaculture pond
    (University of Dar es Salaam, 2009) Yohana, Lawi
    The re-use of treated wastewater from a constructed wetland for aquaculture production has been investigated. Data were collected from an experimental fishpond constructed downstream the HSSFCW at UDSM-WSP system stocked with cichlid fish Oreochromis urolepis. Water quality from the treatment system, within fish pond and outlet of the fish pond were analyzed in accordance with the Standard Methods for the Examination of Water and Waste water (APHA, 1998) and included Nitrate, Turbidity, Organic nitrogen, pH Temperature, Dissolved oxygen, Biological oxygen demand, Total kjeldahl nitrogen, Ammonia, Nitrite and Total nitrogen. Furthermore, an ecological model to simulate nitrogen dynamics and removal in such a fish pond was developed. Results show that, constructed wetland can effectively polish waste water that can be re-used for fishpond culture and that fish can feed exclusively on phytoplankton and grow up to 200g in a period of 120 days. A dynamic and mechanistic mass balance model for nitrogen dynamics in fishpond was developed and simulated using STELLA modeling software and predicted the concentration of organic nitrogen (〖(r〗^2=0.99), nitrate (〖(r〗^2=0.65), and ammonia (〖(r〗^2=0.51). model output predicted that nitrate uptake, decaying and nitrification were the major pathways accounting for nitrogen transformation. They all together account for 62.15 of nitrogen transformation. Sensitivity of model parameters indicated that average nitrogen concentration was most sensitive to phytoplankton specific uptake rate. Further sensitivity analysis revealed that the concentration of nitrogen in any state variable is more affected bi changes in specific parameters included in the fishpond model than other forms of nitrogen in the pond. Model output and results of the processes affecting nitrogen transformations in fishponds and offer possibilities for the most effective management intervention. It is recommended from this study that a more complete integration of the model with respect to other nitrogen pool is required. Also other water quality with respect to fish production such as heavy metals and environmental estrogenicity be investigated.