Study of the microbial population and decomposition of leaf litter in the mangrove ecosystem along the Dar es Salaam coast.

The in situ methane measurements, methane production from both continuous (fermentor) and batch cultures were carried out using leaf litter and other soluble materials as substrates. At both concentrations of 1:5 or 2 grams of leaf litter were found to inhibit methanogenesis in batch cultures. From these results it was concluded that mangrove leaf litter is not a good substrate for methane production. For the soluble substrate trimethylamine with 3 methyl group was found to produce more methane followed by formate and lastly acetate. In the fermentor the methane content was found to be low with the maximum of 0.02 ml per day of methane. This is probably due to low pH observed at the early stages or competition between methanogenic bacteria and sulphate reducing bacteria. In situ values of methane production were found to be variable along the mangrove area with values ranging from 0 to 2.09 ml m-2 day -1. Higher values were measured in the middle part of the mangrove and decreased landward also toward the sea. Mangrove sediments have been found to produce limited quantities of methane and large amounts of sulphide and that the production levels varies within the mangrove areas. The rate of leaf decomposition was studied in situ using litter bag method. Rapid loss in weight was found to occur in the early days of incubation but slowed down with time: Difference in decomposition rates were observed among the three mangrove species studied with decomposition rates of 0.047 %, 0.038 % and 0.015 % per day for Sonneratia alba, Avicennia marina and Rhizophora mucronata, respectively. The presence of high populations of macro-invertebrates and microbial population facilitated the rate of decomposition of the leaf litter in the mangrove sediment. Litter degradation and productivity in mangroves is influenced by many factors and as such we find within the mangroves pockets of varying biological diversity and activities. About 23 species of microalgae were identified using various keys and their biomass was estimated by the amount of chlorophyll extraction from the sediment ranged from 0.27 to 1.33 mg/g. The mangroves toward the sea was to have higher biomass of algae than landward mangroves and in the tidal pools. Generally microalgae species diversity in the mangrove sediment was found to be low as compared to the open waters where hundreds of species have been reported. Pennate diatoms and filamentous cyanobacteria were dominant algal species in Mtoni sediment and were the epiphytic algae found to of and extreme environmental parameters found in the mangrove ecosystems limit the diversity of microalgae in the sediment algae. The thesis is organised in monograph. Chapter one comprise the general introduction and literature review, chapter two is materials and methods used in this research, chapter three is the results and chapter four is the discussion section. At the end there are summary and conclusion.