Modeling And Analysis Of The Change Of Plankton Ecosystem In Jiaozhou Bay For 40 Years

The Jiaozhou Bay (JZB), as a representative embayment in China, is focus research for oceanographers for long time. With the development of industry and agriculture around the bay during last decades, environment and ecosystem in the bay have been severe problems for us. Many achievements have been achieved on physical and biochemical oceanography in the bay according to observation and the numerical studies. However, there is seldom study on the change of ecosystem of JZB with a view to long time, such as interannual and decadal. The main purpose of this paper is to construct an eco-dynamics model that is fit for JZB, to explore the seasonal variation of each variable and the flow characteristics of matter and energy in the ecosystem based on the model, and to analyze the controlling mechanism on long-term variation.We get a review about the physical and biochemical change in the bay according to the former studies and observation first. Then the theoretical model is designed based on NEMURO prototype lower trophic level model. The main features of the modified model are: energy cycling of phosphor is included in, nutrients from riverine input, atmospheric deposition and the Yellow Sea are considered, phytoplanktons and zooplanktons are divided into 2 and 3 groups respectively according to the particle sizes.The seasonal variation of each variable of the ecosystem in JZB during 1995~1996 is simulated by the modified model, and the results matches well with the observational data and the related literatures, which indicated that the model could depicts the main characters of seasonal variation of JZB ecosystem. There are two peaks of phytoplankton mass annually in the bay in 1990s. One is appears in February, when seawater temperature and light intensity of sea surface raise up quickly. At that time, both small phytoplankton (PS) and large phytoplankton (PL) reach a high level of biomass. The other peak appears at about August, because of a large amount of nutrients recruited into JZB from the rivers around. However, the biomass of PL, that is consisted of diatom mainly, stays at a lower level still because riverine input is not main resource of silicate. Results of sensitivity analysis on biology parameters show that the ecosystem is sensitive to the maximum rate photosynthesis of phytoplankton, the optimum light intensity for phytoplankton and half saturation constant for the nutrients, and we should pay more attention on the evaluation of them.The results of 40-year modeling reveal a trend from PL-dominated to PS-dominated in JZB because of differences between variations of riverine input of nutrients. Anthropogenic activities (land-resource nutrients discharge) have a leading influence on the changing trend of ecosystem structure in long-term.