Study On Water Exchange Characteristics And Its Effects Of Coastal Waters

Sea water exchange capacity can partly reflect the physical self-purificationability of the seas. Study of the hydrodynamic characteristics and water exchangecapacity is of great significance for the people to understand the migration andtransformation of pollutants in the water bodies. It can provide strong scientific basisto set up the policies and methods for controlling and reducing the pollution intomarine environment. But for different types of seas, it needs to be researched thatwhat kind of water exchange method is selected to describe its hydrodynamiccharacteristics. The water exchange relation matrix and time scale are applied to studythe water exchange characteristics in Tianjin coastal waters and Pearl River Estuary(PRE) adjacent sea area, and the water exchange influence to the water body functionand the ecological environment is discussed.The concepts, calculation methods and the application scope of water exchangematrix and time scale are described and compared. Both of them could be calculatedby the results of numerical simulation based on the hydrodynamic model andadvection-diffusion model, and could be considered as the extraction and conclusionof the water exchange characteristics, but they focus on different anchor point andtheir data-handing methods are different. Which method is suitable to reveal the seawaters feature should be considered in the study of different water exchangeconditions.The water exchange matrix, which is aimed at the large sea area with weakhydrodynamic effect and uneven mixing phenomenon, was applied to study the waterexchange characteristics of Tianjin coastal waters among the different sub-sea areas.According to the location of main outlet along the coast and residual currentscharacteristics, Tianjin coast shore waters of Bohai bay was divided into9-areas. Thewater exchange matrix was set up to study the water exchange in Bohai bay under theeffects of tidal flow and monsoon wind.The time scale, which is aimed at the small sea area with strong hydrodynamiceffect in PRE and its adjacent sea area, was applied to count the water residence timeof inner, outer and whole Lingding yang with different freshwater discharge andinitial time. The models were validated against the measured data, and the dominantfactors affecting the water exchange characteristics in dry and wet seasons were alsorevealed. Under the influence of seasonal different residence time, the seasonal-spatialvariations of nutrient and Chlorophyll-a around the PRE and the effects on thephytoplankton growth were investigated against the ecological environment surveydata. The relationship were addressed between Environmental factors, the nutrientconcentration, the ratio of nitrogen to phosphorus, the Chlorophyll-a concentrationand the diversity of species of phytoplankton community, and the effects of nutrienton the phytoplankton growth were taken into account.