| Aimed at the hot topic of the marine pollution ecology, this paper mainlydiscussed the influence of nutrients on historical succession of phytoplanktoncommunities in Yangtze estuary and its adjacent sea areas (122-123°E,30.5-32°N), bycollecting the historical data (50years ago) of nutrient and phytoplanktoncommunities. Combined with field survey data from four cruises in April, May andJuly and October of2010, the relationship between nutrients and phytoplanktoncommunities is analyzed; further more, the nutrient influence on succession ofSkeletonema costatum and Prorocentrum donghaiense Lu is discussed in typical area.Main conclusions are as follows:1. In about50years, the concentrations of DIN increased seven times higher above,DIP increased two times or so, SiO3-Si concentration rised slow, and phytoplanktoncells abundance increased rapidly, at the mouth of Yangtze River. The nutrientsconcentration, structure (N/P) and phytoplankton cells abundance were higher inspring and summer, smaller in autumn, but minimum in winter. At the same time, thequantity proportion of diatoms in the total phytoplankton abundance showed a declineand the percentage of dinoflagellate increases, which explained that the N/P ratioincrease made the change ratio of diatom abundance in this area.2. In nearly50years, the HAB mainly occured in spring and summer, the seasonalfrequency had a good relativity with the seasonal nutrient flux from Yangtze River tothe East China Sea. Furthermore, the interannual variability of HAB frequency andthe Yangtze River nutrient flux were also related. These data all showed that theincrease of Yangtze River nutrient flux might be the main influencing factor of thehigh HAB frequency.3. According to distribution of nutrients data in four cruises in April, May and Julyand October of2010, surface concentrations of dissolved inorganic nutrient declinedfrom inshore to offshore areas, the concentration were extremely high and gradientwas large around the area from inshore to122.5oE. The average concentration waslower in10m layer and the distribution was similar to the surface, except less influence by coastal currents and Yangtze River fresh water. The distribution ofDON(dissolved orgnanic nitrogen) and DOP (dissolved organic phosphorus) waspathness. The contour lines N/P indicated a tendency of increase from coast tooffshore. The N/P ratio of10m layer was similar to surface in vertical profile. For thephytoplankton growth, the concentration of DIP was the limingting factor in mostresearch areas, especially the southern area in May.4. In April and July, in the area where diatom was the dominant species (in April andJuly), the surface diatom average density was about10~5cells/L (obvious higher than10m layer), which mainly gathered inshore area where the nutrient conversations werehigh, and N/P, Si/N, Si/P ratios were low due to the influenced by coastal currents. Asfor the area where dinoflagellate dominant (in May), the surface average densityreached to106cells/L (similar to10m layer), mainly gathered in the water influencedby Kuroshio Current, Taiwan warm current and coastal currents, where concentrationsof dissolved inorganic nutrient and DON were minimum, DOP was higher, N/P, Si/N,Si/P ratios were the highest. And the DIP was the linmiting factors for thepyhtyoplankton growth in this area. The results showed that low DIP and high N/Pratio were major cause of the succession of dominant species in phyplanktoncomposition.5. Through analysis of succession of Skeletonema costatum and Prorocentrumdonghaiense Lu in typical area, concentrations of DIN and DIP were high whenSkeletonema costatum growed, DIN and DIP droped rapidly during the successionfrom Skeletonema costatum to Prorocentrum donghaiense Lu, and into the lowestlevel when the Prorocentrum donghaiense Lu cell density was the highest, meanwhilethe DON and DOP increased higher, but SiO3-Si changed slow. DON and DOP mightbe the significant N source and P source. |
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