Biogeochemical budgets and processes in Bandon Bay, Suratthani, Thailand

Water, salt, dissolved nitrogen, and dissolved phosphorus budgets have been constructed for Bandon Bay for the wet and dry periods of 1997 and 1998. The two-box model shows that while most of the dissolved N and P loading is taken up in the estuarine section of Tapi River and Bandon Bay, a significant portion is exported to the Gulf of Thailand. In general, the export fluxes are higher during the wet season than in the dry season. The export flux of DIN is normally dominated by NH4, and generally greater than the export flux of DON, while DIP is exported at about the same rate as that of DOP. Bandon Bay appears to be in balance metabolically (p−r=0), suggesting a very high efficiency within the Bay for recycling organic material. The system consumes about 3% more organic matter than it produces in the dry season and produces about 4% more organic matter than it consumes in the wet season. Tapi Estuary is a net denitrifying system while Bandon Bay is slightly net nitrogen fixing. The presence of benthic algae on the mud flats and the mangrove fringe around the bay could account for nitrogen fixation in the bay. Seasonal variations in biogeochemical rates were attributable to differences in magnitude of freshwater inputs. Under conditions of high river flow, overall rates of net production were enhanced by increased nutrient delivery.