| As the largest semi enclosed inland sea of our country, Bohai sea is surrounded by 13 major cities which located at its north, south and west; these are Shandong, Hebei, Liaoning, Tianjin cities with high population and developed economy. Also it is the important marine economic zone due to its abundant bait and as the spawning and feeding ground for numerous shrimp. However, kinds of pollutants in sewage are pulled into rivers due to dense population and rapid economic growth and finally via estuary into Bohai sea which leads increasing area of pollutant over standard. Particularly the increasing of nutrient is the most prominent.This paper simulates temperature, salinity and concentrations of nutrients by a three-dimensional ecological model which uses MIKE 3 FM hydrodynamics module coupled with Ecolab eutrophication module under considering input of river source and concludes nutrients’horizontal distribution, change trends with time. These results provide a theoretical method for studying nutrients’ecological changes and impacts on ecological environment, also a technical support for improving quality of marine ecosystem.The main contents and results in this paper are as follows:(1) Three dimensional baroclinic numerical module in MIKE3 FM is established to simulate hydrodynamic and thermohaline results which considering Yellow river as point source and four major tidal (01, K1, M2, S2) as boundary condition, also with wind, precipitation, evaporation and heat exchange. The simulation results were validated of credibility and available for ecological simulation by selecting five stations. (2) Considering heat exchange (shortwave radiation, longwave radiation, latent heat, sensible heat & air condition) and source, Yellow river. The boundary condition is set with average data of temperature and salinity in a year. Thermohaline results show that: in winter, temperature of coastal area is generally low but high in central sea which lowest temperature is -2℃ in Liaodong Bay and higher in center with almost 5℃,and the phenomenon homogeneous mixing in vertical is apparent which present the temperature contour is no large difference at a variety of depths.Average of salinity in winter is about 30.8PSU, it is low value due to runoff of Yellow river. Summer time temperature in central area is low but high in coastal and its contour line is parallel to the coastline, and salinity in Laizhou Bay is lower, and there is obviously thermocline and halocline in vertical.Therefore the hydrodynamic and thermohaline simulation results are reasonable and credible to provide reliable basis for the following simulation of ecological simulation. (3) According to characteristics of ecological process in Bohai Sea, lots of ecological parameters are confirmed by literatures. An EU ecological module which includes 7 state variables (ammonium, nitrate, phosphate, phytoplankton, zooplankton, detritus, DO) is established by Ecolab laboratory to simulate water quality. It presents variables’ "source" and "sink".(4) Using MIKE 3 FM three dimensional baroclinic module coupling with Ecolab ecological module to simulate the horizontal distribution and variation of state variables under conditions that setting point source through collecting concentration data of Yellow river and forcing of solar radiation and wind. With kinds of parameters, module simulates changes of chlorophyll, nitrate, ammonium, phosphate, etc. The results come: Nutrients are absorbed when spring bloom outbreaks and accumulated in winter, chlorophyll is present a corresponding double-peak structure, on the other hand, an obvious growth of zooplankton is present in summer and autumn.(5) The results on space distribution on surface come that:due to point source, diffusion effect of current and ecological process, area closed to estuary has high concentration of chlorophyll, nitrate, ammonium, phosphate, etc. But lower in north-east area. Results present that the module could simulate changes in a year of chlorophyll, nutrients, etc. |
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