TEMPORAL VARIATIONS IN MICROBENTHIC METABOLISM AND INORGANIC NITROGENFLUXES IN SANDY AND MUDDY SEDIMENTS OF A TIDALLY DOMINATED BAY IN THENORTHERN WADDEN SEA

Factors controlling seasonal variations in benthic metabolism (O-2 flu x) and dissolved inorganic nitrogen (DIN) fluxes were examined during a 12-14 month period at three intertidal Wadden Sea stations. Since th e flux measurements were made as small-scale laboratory core incubatio ns, the results are primarily related to the microbenthic community (m icroalgae, bacteria, micro-, meio- and small macrofauna) and cannot be considered representative of the total benthic community in the Wadde n Sea. Furthermore, it has to be emphasized that Light intensity durin g daytime simulations were constant and saturating at all times. Benth ic primary production and oxygen uptake appeared to be temperature dep endent with a 'seasonal Q(10)' of 1.7-1.8 and 2.7-4.3, respectively. I nundation had no effect on oxygen fluxes as evidenced by similar sedim ent respiration with and without water cover. A stronger temperature d ependence of primary production in muddy than in sandy sediment indica ted that the overall control in the latter may be complex due to facto rs like macrofaunal grazing and nutrient availability Benthic respirat ion may not be controlled by temperature alone, as sedimentary organic matter content correlated significantly with both temperature and ben thic respiration. Annual gross primary production in high intertidal s andy sediment was 10 and 50 % higher than in low intertidal sandy and muddy sediments, respectively. Since annual benthic community respirat ion was 2 times higher in muddy than sandy sediments, the annual net p rimary production was about 0 in the former and 17-19 mol C m(-2) yr(- 1) in the latter. However, heterotrophic contribution by larger faunal components as well as removal of organic carbon by waves and tidal cu rrents, which are not included here, may balance the budget at the san dy stations. There was no or only weak relationships between (light an d dark) DIN exchange and factors like temperature, sedimentary organic content, and oxygen fluxes. Factors related to nutrient fluxes, such as denitrification and nutrient concentration in the overlying water, may have hampered any such relationships. In fact, DW fluxes at all th ree stations appeared to be strongly controlled by DIN concentrations in the overlying water. On an annual basis, the sediment appeared to b e a net sink for DIN.