SEASONAL-VARIATION IN DENITRIFICATION RATES AND NITROUS-OXIDE FLUXES IN INTERTIDAL SEDIMENTS OF THE WESTERN WADDEN SEA

Variation in denitrification rates, nitrous oxide fluxes and nitrate concentration of the overlying water were studied over 1 yr in sediments from the intertidal zone in the western Wadden Sea, The Netherlands. Denitrification rates were highest in winter and early spring, while in summer the rates were low. Maximum rate was 55-mu-mol N m-2 h-1 minimum rate was 1-mu-mol N m-2 h-1. N2O fluxes were from the sediment to the water column in winter and early spring (maximum 0.6-mu-mol N m-2 h-1), while in summer fluxes from the water column to the sediment were recorded (maximum -0.3-mu-mol N m-2 h-1). For marine systems this is the first time that N2O influxes into the sediment over a considerable part of the year are reported. On an annual basis the denitrification rate and N2O flux were 110 mmol N m-2 yr-1 and O.3 mmol N m-2 yr-1 respectively. Denitrification rates and NO3- fluxes were coupled to the NO3- concentration in the overlying water, as confirmed by NO3- enrichment experiments.