| In recent years, influence by the activity of human beings, eutrophication of the marine environment become more serious and enlarge in level and scale as well, in the Changjiang Estuary and adjacent areas. This induced several serious problems in marine environment and ecosystem such as the worsening of seawater, unbanlence of marine ecosystem and high frequency of HAB.On the base of sumering the studies of the relationship of nutrient and phytoplankton inland and overseas, a series of hot point of the marine environmental ecosystem, such as the limitation status of phytoplankton, the influence of nutrient to the biomass and the structure of species, and the transformation of nutrient by phytoplankton, and so on, were studied emphatically in this thesis. The research work would give some scientific foundation to more studies on the mechanism of HAB in Changjiang Estuary and adjancent areas. The main reseach work and conclusions list as follows: 1. Field experiment and field surveys were conducted in Changjiang Estuary and adjacentareas to investagate the limitation status of nutrients to phytoplankton. The result showedthat:1.1 If there is some kind of limiting factors, the growth of phytoplankton will be limited obviously. In case of erasing the limiting factor, the phytoplankton will grow fast.1.2 At the alongshore of Changjiang Estuary, where the seawater transparency was lower than 1m, was the light limited area both in summer and in winter. The high biomass areas were located in the Zhoushan fishing ground and the north of Changjiang Estuary. The salinity of this area is about 28?1. By contrast the high biomass area in winter was moved to the south east of the investigated area, and the primary production was much lower than that in summer.1.3 By the phytoplankton limitation, the investigated area can be plotted out to 4 regions in summer. I, the light limited area. II, Phosphate latent limited area. Ill,nitrate and phosphate latent limited area. IV, nitrate latent limited area.1.4 It can be plotted out to 3 regions in winter. I, the light limited of phytoplankton area. II, P was the latent nutrient limitation area. Ill, non-nutrient latent limitation area. Light is the latent limitation at the area near the estuary; P is the latent limitation at the diluted area, and changes of season are not obvious.1.5 At the both side of the boundary of salinity 31, N and P limitation of phytoplankton changes actively. N and P are latent limited factors in summer; and there is no latent nutrient limitation in winter.1.6 There is no Si and Fe limitation of phytoplankton in the researched area2. A study was conducted to investigate the influence of nutrient to the biomass and the structure of species and the transformation of nutrient by phytoplankton in Changjiang Estuary and adjacent areas. The result showed that:2.1 In the field experiment, the biomass of phytoplankton increase with the increase of concentration of phosphate at the P limited conditios. The biomass of phytoplankton increase with the increase of concentration of nitrate at the N limited conditions.2.2 In the estuary area, under the high nutrient concentration condition the influence of concentration of nutrient is stronger than the influence of nutrient ratios. The promotion to the growth of phytoplankton of adding nutrient at the far area of the estuary is more obvious than that at the near of the estuary.2.3 From the culture results, on the conditions of blooming, the blooming species would keep the dominated species if there were abundant nutrient. It hard for the other species to get the dominated status.2.4 On the conditions that there were no blooms the changes of species of phytoplankton were obvious. Prorocentrum Donghaisense could live strongly on the condition of low nutrient concentration, and it would be replaced by diatom (Skeletonema) on the nutrient enriched condition.2.5 On the condition of high N/P ratio (higher than Redfield ratio), the uptake to n...
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