Annual cycle of ammonium and phosphate fluxes across the sediment-water interface in coastal marine environment (the Seto Inland Sea)

A study on nutrient regeneration processes and measurement of their fluxes at the sediment-water interface was carried out in two different stations of Shido Bay (the Seto Inland Sea, Japan). Seasonal variations in bottom-water, oxygen uptake and benthic fluxes were measured during 1999 to 2000. The sediment oxygen consumption (soc) ranged from 16.6 to 21.4 mmol m(-2) d(-1). Net fluxes ranged from 471 to 2264 mu mol m(-2) d(-1) for ammonium (NH(4)(+)) and 39 to 216 mu mol m(-2) d(-1) for phosphate (PO(4)(3-)). A step-wise regression model indicated that bottom-water temperature and DO described 73% and 72% of the variability in measured rates of NH(4)(+) and PO(4)(3-), respectively. Concerning the stoichiometry of oxygen (O), nitrogen (N) and phosphorus (P) emission from sediment, an annual average of O:N and O:NH(4)(+) flux ratios is 19.6 and 18.3, respectively, indicating that denitrification was occurring in Shido Bay. N:P ratio showed variable values (9.2 to 22.2), which the yearly average of N:P ratio (13.2) was approached for estimating benthic denitrification, suggested that about 93.4 mu mol m(-2) d(-1) was loss to N(2) gas, which was 7% based on the N flux. An annual average of N and P fluxes showed that the sediments were supplied to the bottom-waters with equivalent to 33% and 22% of primary production N and P. respectively, requirement by phytoplankton of Shido Bay.