| 其他摘要 | The spatial distribution characteristics for the surface sediment samples from Sishili Bay and northern Yellow Sea, and temporal distribution characteristics for the century-long time core sediment from Sishili Bay were researched in this thesis. It was analysed how the different kind and extent human activities, sedimental environmental and climate change had impacted the diatom assemblage in the sediment. Furethermore, it was discussed how to use the recent diatom assemblage in the sediment to indicate the environmental changes in a relatively appropriate way.In spatial scale, based on the kind and scale of human activities (wastewater discharge, shipping travel, marnie aquaculture and waste dumping), 20 sites were selected in the Sishili Bay; in addition, 8 sites in the central northern Yellow Sea that was less impacted by human activities were also chosen as a contrast zone to study the indication of environmental changes from recent siliceous assemblages. For the surface sediment of Sishili Bay, totally, 85 micro-phytoplankton silicious species were discovered including 12 dominant species, and the species diversity and richness index was 3.45 and 7.04, respectively. The cell abundance of diatom and silicoflagellate in inshore areas ranged from 368 to 20335valves/g DW with an average of 3909valves/g DW with a trend of zone A (6886 valves/g DW, near the household wastewater outfall) > Zone D (6406 valves/g DW, near the marine waste dumping site) > Zone B (2494 valves/g DW, around the Yantai Port channel) > Zone E (2097 valves/g DW, near the industrial wastewater outfall) > Zone C (1573 valves/g DW, the marine aquaculture area). The diatom distribution characteristics in the inshore area were closely related with the sediment grain size and human activities. The household wastewater discharge in Zone A and marine waste dumping in Zone D had caused nutrient enrichment in these two zones, which may partly lead to the fact that the cell abundances of diatom and silicoflagellate in Zone A and Zone D were higher than other zones. The sediments in zones mainly affected by the marine aquaculture and industrial wastewater discharge were coarser than other zones in the inshore area, so the diatom and silicoflagellate debris had less abundance in these two zones. The high frequency of ship movements in Zone B can disturb the deposition of diatoms in the surface sediment and thus decrease the diatom abundance. The aquaculture of filtering species could cause phytoplankton density to drop. The high grazing pressure from the scallops in Zone C can significantly decrease the abundance of phytoplankton in the water column and consequently reduce the amount of diatom deposited in the sediment. Thus, the study for the surface sediment of Sishili Bay well showed how the different kind of human activities impacted the diatom assemblage in distinct ways.For the surface sediment of contrast zone of northern Yellow Sea, only 39 species were found, including 3 domiannt species, and the species diversity and richness index was 2.04 and 3.6 respectively. The cell abundance in the offshore area ranged from 716-2060 valves/g DW，averaged 1509 valves/g DW. The difference of diatom assemblages between the inshore and offhosre areas was found closely related with the impact gradient of human activities. Correlation analysis showed that the diatom abundance in the sediment was positively related with the nutrient level in the water column; the nutrient concentrations in the inshore area were higher than offshore due to the intense human activities such as wastewater discharge and waste dumping. Thus, the comparisons of inshore and offshore area presented that the spatial distribution of diatom assemblage in different zones could well indicate the impact gradient of human activities. In temporal scale, totally, 62 species were identified from the two core sediment. It was found that the diatom assemblages in the cores kept relatively stable before the 1980s and were dominanted mainly by planktonic species with the cell abundances generally belower than 10000 valves/g DW. However, from 1980, significant changes had occurred for the diatom assemblages. For example, the percentage of planktonic dominant species reduced with the increasing percentage of the tychoplanktonic species and benthic species, and the cell abundances were higher than 10000 valves/g DW after 1980. The eutrophication indicative species Paralia sulcata and warmwater species Cyclotella stylorum and Dictyocha fibula had also experienced an increasing trend from the 1980s. Additionally, the diversity and richness index were higher compared with that before 1980. The temporal distribution characteristics of diatom assemblage in the cores had well indicated the human activities and climate changes after the 1980 in some degree. Since the reform and opening up in the end of 1970s, Yantai city has been experiencing great development, with the establishment and usage of the wasterwater treatment plant and waste dumping zone, more and more waste were put into the bay, which definitely increased the trophic status of the coastal area and caused the higher concentration of of diatom assemblages in the sediment. The large area culturing of filtering bivalve species and shipping business in the bay since that period also experienced blooming, as we discussed for the surface sediment, these two kind human activities could decrease the recent preservation in the sediment in some scale; however, they were useful for the species diversity to keep a high value. Two warm water species were identified in the core sediments, Cyclotella stylorum and Dictyocha fibula. The distribution trend of the two species during 1960-2008 were similar with that of the air temperature record, especially after 1989; both cell abundances of the two species and the air temperature had an obvious increase and matched very well from that time. Thus, the indicative species in the sediment of Sishili Bay had a good potential to trace back the local climate changes.Summarily, by comparing the spatial differences of diatom and silicoflagellate in the modern surface sediments of different zones which were under distinct human activities and the temporal differences of them in two core sediments, this thesis not only showed the temporal and spatial distribution characteristics of diatom silicoflagellate in Sishili Bay and adjacent area of northern Yellow Sea and fill a vacancy for that research in those areas, but also set an example for similar research of tracing back the coastal environmental changes of the coast through the recent diatom in the sediment. Furthermore, the study of core sediment research in the Sishili Bay, which analyzed the relationship between the recent flora and human activities and climate changes, had collected some useful data and experiences for the future paleoenvironmental construction of local environment. |
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