Tidal residual is very important to the transport of water particles, nutrients, plank-ton, etc. in the coastal sea. Eulerian scheme and Lagrangian scheme are two different ways to get thetime averaged residual. Solution of the Bohai Sea's hydrodynamic system using a semi-implicit layer aver-aged numerical model yielded different direction Eulerian and Lagrangian tidal residuals. The latter werestronger than the former in most sea areas. Their different directions produced different circulation patternin some areas. Compared with the Eulerian residual, the Lagrangian residual seemed to be more in accordwith the observation.

建立了一个与水动力模型耦合的、以浮游植物生物量、无机氯浓度、磷酸盐浓度、底碎屑含碳量为变量的三维生态模型，模拟出了与观测基本相符的渤海浮游植物量和初级生产年变化规律、水平及垂直分布的季节变化。渤海的浮游植物生物量和初级生产均呈双峰结构，夏季为高生产季节。垂直湍流混合与生物量密切相关，水体越稳定越有利于生物量的增加。模型对于磷与碳之比及无机氮半饱和常数比较敏感，需加强对敏感参数的实验测定。该模型可以用于浮游植物动力学过程的研究.

以所建立的三维生物- 物理耦合模型估算了渤海碳循环过程，探讨了水平对流、河流输入、氮磷循环、非保守输运等过程对渤海低营养级系统的影响。渤海是大气二氧化碳微弱的汇。在碳循环中，总光合生产的13.7%进入营养的高一级，76.8%被自身呼吸消耗。营养盐再生主要源于内部生物地球化学循环，有机物的矿化过程是营养盐从有机向无机形态转换的主要机制. 水平对流过程降低了海域生物量，有利于减轻局部海域的富营养化程度。河流输入只引起局部海域系统调整，渤海生物自净能力十分有限，控制限制生物生长的营养盐的排放有利于减少浮游植物的生物量。

Long-term transport processes in coastal seas with time scales from weeks to seasons time scale are controlled by residualcirculation. In the Bohai Sea, an ultrashallow shelf sea of China, tidal residual is almost the dominant factor to the circulationdue to slight stratification and weak wind in summer. In order to establish an adequate hydrodynamic base to the ecosystemdynamics of the Bohai Sea, the differences of tide-induced Lagrangian and Eulerian mean circulation are discussed andcalculated in this contribution. The Stokes drift is analyzed theoretically. According to Longuet-Higgins [Deep-Sea Res. 16 (1969) 431], the Lagrangian flow is the sum of the Eulerian flow and the Stokes drift that is induced by the mean kinetic energyand coastal nonlinear interaction. Stokes drift is large in the coastal sea and in areas where the vorticity and/or divergence arelarge. Vertical mass transports by Stokes drift are also the result of nonlinear interaction of current, water level and topography.Hamburg Shelf Ocean Model (HAMSOM) is applied in the Bohai Sea to simulate the tides and tidal currents. The tide-inducedLagrangian mean circulation and the Eulerian one are calculated at the same time. In the area where the Stokes drift is in thesame direction as the Eulerian residual, the Lagrangian one is stronger than the Eulerian one. Where they are pointing inopposite directions, the Lagrangian one is small, like in the southwest of the Bohai Bay, Liaodong Bay and Bohai Strait. TheLagrangian residual current flows into the Bohai Bay along its southern bank causing deposition of Huanghe River sediments.This is in agreement with observations.