Study On Water Environment Effects Of Coastline Changes In Liaodong Bay

Liaodong Bay is located in northeastern of the Bohai Sea. It is a typical semi-closed and shallow bay. With the rapid development of local economy in Liaodong Bay, a huge amount of pollutants were poured into the bay which made the concentration level of nutrients getting higher and higher. So, it is very important to build a model to simulate the hydrodynamic situation and water environment in Liaodong Bay.Based on MIKE, a three-dimensional baroclinic model of the Bohai Sea was constructed with unstructed triangular mesh, considering the factors of precipitation, evaporation, cloud cover, relative humidity, air temperature, river discharge and so on. The model was calibrated by the validation of measured data of 12 tidal stations,4 current stations, and 4 ocean stations of temperature and salinity. The results showed that the model could reproduce the hydrodynamic and thermohaline characteristics of the Bohai Sea well, so it could be used to provide hydrodynamic and thermohaline background field for the hydrodynamic and water quality model of Liaodong Bay.Depending on the hydrodynamic model of the Bohai Sea, a small model concentrated on water quality for Liaodong Bay was built and then the simulated tidal current field and nutrients as well as chlorophyll-a were mainly analyzed. The results show that the tidal current of Liaodong Bay is a regular semi-diurnal current, whose main feature is the reciprocating flow and direction is NE-SW. Simulation of water quality reproduced change process of phytoplankton and nutrients in Liaodong Bay in 2005. The model showed the typical bimodal phenomenon of phytoplankton well and the mechanism of this phenomenon was explained combining the change process of nitrogen and phosphorus nutrients. The nutrient composition structure of Liaodong Bay was analyzed according to N/P ratio (ratio of nitrogen to phosphorus). The results show that Liaodong Bay can be classified as a phosphate-limiting moderate-level nutrient area.With the application of the model, the impact of coastline changes on hydrodynamic environment in Liaodong Bay is predicted from three aspects of flow field, water quality and nutrient composition in Liaodong Bay. The results show that coastline changes won't change the hydrodynamic characteristics widely in Liaodong Bay, with affection mainly concentrated in the vicinity of offshore area. Coastline changes may exacerbate water pollution. Besides this, it leads to the decrease of average chlorophyll-a concentration, the increase of average active phosphate concentration and inorganic nitrogen concentration. The value of D/P rises in spring, summer and autumn but it decreases in winter. Coastline changes make the role of phosphorus restriction generally strengthened.