Spatial and temporal variations in water column nutrient concentrations in a tidally dominated mangrove creek: Chwaka Bay, Zanzibar

Spatial and temporal variations of dissolved inorganic nutrients, (phosphate, ammonia, nitrate and nitrite) were investigated in the Mapopwe Creek, Chwaka Bay, Zanzibar. Results indicate that there is a strong spatial variability in the nutrients in the creek with concentrations decreasing as the water traverses the waterway towards the open bay. There were significant differences in the concentration of ammonia with respect to wet and dry seasons, with average values of ammonia being higher in the dry season than during the wet season. However, this situation was reversed for nitrate/nitrite. It is thought that this may be due to a number of contributing factors such as changes in benthic oxygen concentrations, differences in water salinity, and changes in water movement and exchange with the open bay. Also, water-column primary production and benthic microbial processes are thought to play a role. Overall, this study showed no net export of these dissolved nutrients from the Mapopwe Creek into the adjacent bay.