Ecosystem Dynamic Models For South Yellow Sea And An Aquaculture Bay

South Yellow Sea(SSY) is an important offshore sea for China, and it is significant to study its ecosystem processes for understanding ecological mechanisms. Sanggou Bay(SB) is a typical aquaculture coastal area, and research on its ecosystem status is helpful to appropriate culturing activities in a such sea. The dissertation aims to model ecosystem processes for each of seas in different scale. The fist step is establishing a hydrodynamic model to reproduce physical processes of each sea. Based on the model, an ecosystem model is then developed by selecting variables and parameterizing bio-chemical processes. After validation, the model results are used to analysis the ecological characters for both seas.The hydrodynamic model of SYS almost completely includes the physical processes, such as tides, wind force, wave mixing, circulations, and so on. Variables of the SYS ecosystem model are phytoplankton, zooplankton, nutrients and detritus. For SB models, the effect of aquaculture to hydrodynamics is taken into account, and ecological elements include dissolved organic matter in addition to above variables. The processes of depletion or expiration of baits and nutrients by shellfish and large algae are parameterized. Based on the ecosystem model, the evaluation models of carrying capacity(CC) of shellfish, large algae, and fish are setup according to balance relationships between substance supply and demand or a nutrition dynamic relation respectively. The followings are obtained:For SYS:1) The wave mixing and tidal current make vertical diffusion coefficients crease with 10-3～10-1 m2/s in upper layers and lower layers respectively. They mix the coastal waters more uniform vertically, and enlarge the thickness of the mixed layers of both surface and bottom and increase the thermocline strength in deep sea areas. With tides, the SYS warm circulation and coastal circulations in winter, and Taiwan warm circulation, China's coastal circulation and circulations of SYS central areas in summer are all weakened compared with results without tides. Besides, the direction of Korea coastal circulation in summer is reversed in counterclockwise. In this case, circulations of SYS central areas are southward and with lower velocities, while northward lack of tidal forces. 2) Both the primary production and the phytoplankton biomass are highest in spring, and second highest in summer, lowest in winter. A significant bloom happens in mid-April. In spring, the net inflow of phytoplankton of SYS is always positive and great, which is helpful to bloom formation. While in summer the net inflow is often negative. In most areas of SYS, the phytoplankton growth is limited to phosphorus.3) In the west coastal area, phytoplankton biomass is high from late April to early September, and stratification is unobvious. In areas near Changjiang River the biomass is highest on the whole in SYS, and the significant bloom appears in May. Along with distance increase from the river inlet, the biomass generally increases firstly and then falls. In the area, phytoplankton growths object to light limitation, and strong mixing processes preclude accumulation of phytoplankton. In SYS central areas, the stratification of phytoplankton is obvious from April to November, and the prominent bloom happens in late April. From May the subsurface layer, which has the highest biomass, deepens gradually. In August and September, the layer's top is up to 30 m deep. For east areas, the ecological features are similar to central areas. The low layer exist upwelling flows, where nutrient concentration is high.4) Wave mixings and tides play important roles in formation of ecological characters. Wave mixings delay and strengthen the spring bloom. Regardless of the mixings, the bloom moves up 13d. The rationality of addition of the mixing to the model is analyzed.5) Runoff increases SYS biomass, especially for estuary.For SB:1) Observation indicates aquaculture activities reduce flows of culturing layers. By laying porous plates with friction, a model is developed to reproduce physical processes of the area. The friction coefficients are given. The half-exchange duration of SB is 7d without aquaculture,12d with shellfish only, and 16d with both shellfish and kelp culturing. In northwest and southwest areas of SB the water exchange ability is poor.2) As a whole, the phytoplankton biomass is relatively low in winter and high in summer, and appears a weak peak in February and a maximum in September. This is a common feature for culture areas of kelp, oyster and scallop. The ecological characters are related to aquaculture. In shellfish-culture areas, nutrient densities are high in summer and autumn, which is related with shellfish excretion.3) The CC of scallop is great in winter and autumn, small in spring and summer, and minimum in April. The annually averaged CC is 53 ind/m2, and the total CC is 10.1 billion individuals. The present density should not be enlarged. The CC of oyster is high in winter, low in summer, and lowest in late August and highest in mid-February. The CC is 76 ind/m2, and a total CC is 41.1～51.7 billion individuals for oyster-culture areas. The recommended density is 39333 ind per MU. The total CC of kelp is 21250 t, and the CC in density is 384 g/m2 i.e.3.84 ind/m2. A recommended seedling density is 4 ind/m2. Without addition of baits, the CC in a fish cage is 6.81 g/(a·m2). SB may stock 850t/a fish.