Study of Physical Self-Purification Capability in the Offshore Area of Jiaozhou Bay
Jiaozhou Bay is treasure of Qingdao which is given by nature. As the rapid development of industry and marine aquaculture, water quality has been severely polluted due to the discharge of large quantities of untreated industrial wastewater and urban sewage. Based on the Estuarine, Coastal and Ocean Model (ECOM), a three dimension Lagrangian particle model was built to simulate the trajectory of several pollution sources into Jiaozhou Bay and study the physical self-purification capability. The results presented here provided a scientific basis for the marine environmental protection and management. Jiaozhou Bay (JZB) is a typical semi-enclosed bay situated in the southern part of Shandong Peninsula (35o58´-36o18´N, 120o04´-120o23´E), with an area of 372 km 2 and an average depth of 7 m. In recent years, with the rapid development of industry and marine aquaculture, the pollution of JZB becomes more and more serious. One of the important reasons that cause the water quality deterioration can be attributed to the land source pollutant. The environment pollution problem increasingly aroused people's attention, thus, the research on the transportation of the land source pollutant and the physical self-purification capability has great significance in marine environmental protection and management. The 3-D Lagrange model can be given the 3-D trajectory, residence time, influence scope etc. and has widely applied in the ocean environmental protection realm (1) . The article set a particle tracking model base on the Estuarine, Coastal and Ocean Model (ECOM), simulate the range of the wastewater influence and study the physical self-purification capability of JZB, which provide a science basis for the local marine environmental protection. II. PARTICLE TRACKING MODEL A 3-D particle tracking model coupled with a hydrodynamic model was developed in this study. The hydrodynamic model was modified by introducing dry-wet grid technology (2-3) based on the Estuarine, Coastal and Ocean Model (ECOM), which provided the physical parameters (tidal elevation, current and eddy diffusion coefficients) to drive the particles transport process in the model. The variable boundary ECOM was successfully applied in Jiaozhou bay, Bohai bay and Jiaonan sea area (4-6) , therefore, the article briefly introduced the 3-D Lagrangian particle tracking. The trajectories of the particles were calculated following the scheme given by Dimou and Adam (7) . A random-walk particle tracing scheme has been designed which calculates the displacement of as the sum of an advective deterministic component and an independent, random-walk component which statistically approximates the turbulent eddy diffusion processes. The values of the diffusivities were taken from the hydrodynamic numerical model. Therefore, given the initial position of the particle as P(x,y,z,t), the position of the particles P(x,y,z,t+1) passed by a certain time step t were calculated as: