A laboratory study was conducted to determine the denitrification potential of intertidal sediments of the river ScheIdt, to assess how the tidal fresh water wetlands of the river ScheIdt have the potential in controlling nitrogen input to the sea. The potential was estimated by the steam distillation technique during long and shortterm incubation experiments. The method was based on measuring the disappearance of endogenous or added nitrate as KNO3 solution in sediment samples collected at one of the ScheIdt tributaries, the Durme between December 1995 and March 1996. In all experiments where nitrate was added, a rapid decrease of (NO3- + NO2-)-N in the water overlaying the sediments was found. During long-term incubation experiments it was not possible to follow closely how fast the added nitrate was depleted because nitrate was consumed within a few hours after incubation. For that reason short-term incubation experiments with different nitrate concentrations ranging from 5 to 100 mg NO3-N.l-1 were performed. During the short-term incubations, the result shows a systematic rapid disappearance of (NO3- + NO2-)-N in the water overlaying the sediment at all levels of added nitrate.Most of the added NO3-N from the overlaying water disappeared indicating rapid reduction of the NO3-N that is diffused into the underlying sediment column. Linear correlation analysis of the data indicate that, the disappearance rates were 0.5398, 0.7414, 1.3193, 1.8198 and 2.8497 mg NO3-N.l-1 hr-1 for 5, 10, 20, 50 and 100 mg NO3-N.l-1 respectively. The consumption rate varies depending on the initial nitrate concentration. The rate increased as the concentration of nitrate increases. From our data it also appeared that, plotting the log (NO3- + NO2-)-N as a function of time, gave straight lines with high correlation coefficients, indicating the disappearance rate followed the first order kinetics. The results obtained in this study indicate that the intertidal sediments of the river Scheidt can function as an effective sink for NO3-N.
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