Benthic nutrient flux in a shallow coastal environment.

Ammonia and nitrate efflux from a fine sand in Carmarthen Bay was studied by incubating undisturbed cores of sediment on board ship. At the end of each incubation, the macrofaunal and bacterial biomass in each core and the organic content of the sediment were determined. Oxygen consumption was measured in another series of cores. The relationship between ammonia flux and biomass was investigated using a lattice of hypotheses approach to multiple linear regression, where all possible submodels of a general model are fitted. Ammonia flux was significantly related to the biomass of polychaetes and molluscs and "other macrofauna" but the inclusion of bacterial biomass did not improve the regressions. The estimated annual efflux of ammonia was 778 mmol N m-2 which is 44% of the estimated annual nitrogen demand of the phytoplankton. However, at the time of maximum primary production in June, only 16% of the phytoplankton requirement for nitrogen was met by benthic ammonia flux. Nitrate efflux was an order of magnitude less than that of ammonia and reached a maximum in the autumn. No significant relationship was found between oxygen consumption and macrofaunal or bacterial biomass at any time of the year.