3D model system for hydrodynamics, eutrophication and nutrient transport

摘要

The existing MIKE 3 model system consisting of modules for hydrodynamics and eutrophication has been improved to include a description of exchangeable pools of nitrogen (N) and phosphorus (P) in the sediment. It is now possible to make a complete mass balance for N and P in a model area and to make calculations of the transport of nutrients across sections in the model. Besides the new feature the model system is also able to simulate water levels, current fields, concentrations of nutrients, chlorophyll, dissolved oxygen, biomass of eelgrass and benthic macroalgae. The model system has been calibrated (1998) and validated (1997) on a temperate shallow Danish fjord, (Odense Fjord, Funen). The fjord, which covers 64 km~2 and has an average depth of 2.5 m, is connected to the sea through a narrow entrance. The hydrodynamic module was able to reproduce the water levels and the salinity satisfactorily at three stations in the fjord for both years. At two stations weekly data of water chemical parameters, such as total P & N and inorganic nutrients, were available for the calibration and validation of the eutrophication module. Based on model results a nutrient budget was set up for 1997 and 1998. Due to low precipitation the 1997 load of N and P was about 60 % lower than in 1998. The yearly retention of N for the two years was 35 % and 15 % and was caused by the burial of N in the sediment and denitrification. The yearly retention of P was negative,-121% and -28 %, for the two years due to the release of P from the sediment. This is consistent with the implementation of the nutrient treatment of domestic sewage in the early 1990's.