As part of an EIA approval process A/S Fynsværket has commissioned DHI to evaluate the effect of an increased cooling water discharge into Odense Fiord, Denmark. The increased discharge has lead to a concern that the water quality in Odense Fiord may deteriorate due to an increased eutrophication level.

Using a three-dimanensional modelling approach that linked the hydrographical, chemical and biological systems it was possible to establish interannual nutrient budgets for the entire fiord as well as for sections of the fiord. To allow for a complete mass balance for nitrogen (N) and phosphorus (P) and to enable calculations of the transport of nutrients across sections, a sophisticated description of exchangeable pools of N and P in the sediment was included.

The nutrient budgets revealed a significant internal loading of P from the sediment after implementation of N and P treatments of domestic sewage years ago and a retention of nitrogen in the range of 15-35 % of the load from land.