Release of nitrogen compounds following resuspension of sediment: Model predictions

Simulation models were used to predict the concentrations of dissolved organic nitrogen (DON), ammonium and nitrate in sediment pore waters, under various conditions. The quantity of particulate organic matter (POM) undergoing decomposition varied from 5–85 mmol C m−2 d−1; this POM had C:N ratios of 5 or 10, and was distributed in three different ways. The POM was either located close to the sediment surface, or decreased linearly from the surface, or was completely mixed into the sediment. The effect of resuspending the sediment to various depths, for this suite of profiles, was determined. The different distributions gave unique patterns, but it was concluded that sediment must be resuspended to considerable depth before any major contribution was made to the overlying water. Thus, at the highest POM degradation rate, in order to get a liberation of ΣN of 5 mmol m−2, it was necessary to resuspend the top, linear and mixed distributions to depths of 2.4, 1.2 and 0.8 cm respectively. The model predicted that after mixing of the latter to 2.4 cm, profiles of ammonium and other molecules had returned to pre-mixing values after 5 h. It was predicted that resuspension would not increase the quantity of nitrogen molecules exported to the overlying water, but it would affect the timing.