Research On Modelling Water Exchange And Nutrient Budget In Jiaozhou Bay

A three-dimensional dispersion model and a physical-biological coupled model were developed and applied to Jiaozhou Bay in order to study the water exchange and nutrient budget that are closely related to eutrophication processes. This study lays a constructive foundation for further research on the decadal variation of coastal eutrophication and its mechanism in the near future. Significant results and useful conclusions have been achieved in the following aspects:Firstly, Princenton Ocean Model was applied to Jiaozhou Bay in order to provide the physical parameters, i.e., elevation, velocity and diffusivity, for the study of water exchange and nutrient budget. The tidal simulation agreed quite well with drift experiments and water elevation observations at the Dagang tide station. It indicates stationary wave features control the propagation of the tidally-driven system. Tidal currents in most areas flow back and forth. The modelled coamplitude and cophase of the M2 component shows that tidal currents turn clockwise as they propagate in JZB, with maximal phase and amplitude difference of 3.0 and 5 cm, respectively.Secondly, the modelled average residence time was about 52 days, ranging from less than 20 days in the deep part near the bay channel, the only passage connecting the bay to the Yellow Sea, to over 100 days in the shallow area in the northwest. The spatial difference of average residence time was controlled by tidal residual currents and the distance to the bay channel. The average residence time between surface and near bottom waters was similar due to strong vertical tidal mixing. The modelled tidal exchange rate was uneven in the bay, and consistent with 228Ra observations. The temporal evolution of the passive tracer accords with the evolution of the rain fraction after the rainstorm in August 2001.Thirdly, methods for calculating environmental capacity were summarized and discussed. The author points out, for the first time, that environmental capacity cannot just simply be taken as the maximum permitted discharge amount for the marine environment to meet the determined standard. To clarify, the environmental capacity defined here is the discharge amount for normal environmental functions, and for the total economic production value of the companies (or communities) generating pollutants to maximize at the same time. The methods in determining the reasonable seaward pollutant discharge are suggested, for the above point of view.Fourthly, the long-term change in water temperature was simulated and the heat budget discussed. This part is necessary for the model study of nutrient seasonal variation and the basis of the long-term eutrophication process in Jiaozhou Bay. Temperature decreasing in 1960s and 1970s and continual increasing in the recent 20 years accords with the climate change in the in the adjacent sea area, i.e., Yellow Sea. EOF analysis was used to obtain the eigenvectors and their time coefficients of the temperature in winter and summer, respectively. The first mode satisfactorilydescribes the spatiotemporal variation, since its significant percentages of the accumulated variances > 98%.Fifthly, the diapycnal eddy diffusivity was calculated based on the intensive observation of vertical diffusion conducted in August 2001 in Jiaozhou Bay. The results show that the temporal variation rate of the vertical diffusion coefficient is so complicated that the diapycnal eddy diffusivity could change by one order of magnitude per tidal cycle. This work helps to provide significant background for the further research on sensitive analysis of vertical diffusion.Sixthly, after establishing a physical-biological coupled model, the sensitivity of its parameters was discussed and variation in limitation factors including light density and nutrient concentration are analyzed. The coupled model is more sensitive to phytoplankton maximum growth rate, respiration rate, death rate and zooplankton grazing rate, while other parameters such as half saturation constants and remineralization rate a...