Modelling of an estuarine eutrophication gradient

Roskilde Fjord represents an estuarine eutrophication gradient with annual average salinities varying from 11 to 18°C and average summer chlorophyll concentrations ranging from 3 to 25 mg m−3. A PC based one-layer and one-dimensional hydrodynamic model and a transport/dispersion model served as the basis for a eutrophication process model with 12 state variables. Water levels and salinities were well predicted. Objective function yielded values of 0.13 for dissolved oxygen, 3.63 for chlorophyll, 8.44 for inorganic nitrogen and 3.68 for phosphate for the water quality model during a design period covering the spring 1985. Comparisons with mass balances calculated by means of a simple box model indicated the necessity of including a resuspension and sediment transport description.