太湖梅梁湾三维水动力学模型的研究　Ⅱ.营养盐随三维湖流的扩散规律

STUDIES ON THREE-DIMENSIONAL HYDRO-DYNAMIC MODEL IN MEILIANG BAY OF TAIHU LAKE Ⅱ. The Diffusion of Nutrient Salt Under the Action of Three-Dimensional Currents

建立了太湖梅梁湾三维营养盐浓度扩散模型，研究了在三维湖流的作用下，营养盐随风场的扩散情况。结果表明：（1）当梁溪河和闽江口两个污染源同时存在时，西北风最有利于营养盐浓度的扩散，顺着风向形成了一条西北一东南走向的污染带；而东南风却最不利于营养盐浓度的扩散，使得污染范围仅局限于污染源附近。（2）太湖海梁湾冬季比夏季更利于污染源浓度的扩散。（3）当风向有利于污染源浓度扩散时，随着风场强度的加大，污染源的扩散范围逐渐增大；反之当风向不利于污染源浓度扩散时，随着风场强度的加大，污染源的扩散范围反而减小。（4）当风向有利于污染源浓度扩散时，营养盐浓度的分布是自上而下递减的；反之当风向不利于污染源浓度扩散时，营养盐浓度的分布是自上而下递增的。

This three-dimensional diffusion model was developed to mainly study the distributionof nutrient salts under the achon of three-dimensional curmnts in Meiliang Bay of Taihu Lake.Regarding the pollution soaree in the Liangxi fover, the northeast wind is the most (the southwestWind is the least) benefical to the diffusion of pollutants. In genend, two pollution sourees exist inMeiliang Bay at the same time, in which case the northwest wind is the most (the southast wind isthe least) benefical to the diffusion of pollutants, and forms a pollution zone along the direction ofwind. As the northem wind prevails in winter and the southem wind in summer, winter is moreedvantageous to the diffusion of pollutant than summr.The variation of wind speed also affects the diffusion of pollutan. The extent of pollutionincreases with the increase of wind speed when the direction of wind is favourable, but decreaseswith the increases of wind speed when the direction of wind is utifavourabe. Ih addition, theconcentration of pollution decreases from the surfase to the bottom in the case of the direction ofwind being favourable to the diffusion of pollutant but increases from the surfase to the bottom inthe case of the direction of wind being unfavourable.