Fluxes of dissolved inorganic nutrients: NH+4, NO-2, N-3, PO34 and Si(OH)4 from near shore sediments of Gazi Bay were measured in situ within mangrove, sea grass and coral reef biotopes using benthic flux bell-jar chambers of cross-sectional area 0.066 m2 and volume 0.0132 m3. The objectives were: (1) to determine the influence of benthic fluxes, fluvial discharge and seasonal variations on the nutrient budget in the Bay waters; (2) to determine the effect of tidal and spatial variations on nutrient loads in the water column and (3) to establish the relative importance of the nutrient sources with regard to total community production of the Bay.
The directly measured fluxes ranged from -270 to +148 µmol NH+4-N/m2/h; -60 to +63 µmol NO-2-N/m2/h; -79 to +41 µmol N-3-N/m2/h; -79 to +75 µmol PO34-P/m2/h and +30 to +350 µmol Si(OH)4-Si/m2/h for and respectively. It was established that benthic fluxes are the major sources of dissolved inorganic NH+4, NO-2and Si(OH)4 while fluvial sources are important for N-3 and PO34into Gazi Bay waters. Seasonal variations had an appreciable effect on the PO3-4, fluxes, N:Si ratio, river nutrient discharge, plankton productivity and important environmental factors such as salinity and temperature. Tidal and spatial variations had no significant effect on nutrient concentrations and net fluxes within the water column. The results imply that benthic fluxes are largely responsible for the nutrient dynamics of the near shore coastal ecosystems especially where direct terrestrial inputs do not contribute significantly to the nutrient budget.
© 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Gazi bay; Nutrient sources; Benthic fluxes; Fluvial discharge; Community production; Coastal ecosystems