Studies On Community Structure And Size-fractioned Structure Of Phytoplankton In Yellow River Estuary And Its Adjacent Area In Summer And Autumn

In this thesis, the species composition, cell abundance, dominant species and biodiversity of phytoplankton in Yellow River estuary and its adjacent area were studied based on the samples collected during two cruises in July 2009 and September 2010 (net-phytoplankton samples for Jul. 2009, water samples for Sep. 2010). The correlations between phytoplankton and environmental factors were discussed. The method of Chlorophyll a sizing was applied to study size-fractioned structure of phytoplankton in Yellow River estuary and its adjacent area. The major objective of this study is to understand the phytoplankton community structure more comprehensively and provide fundamental information for further research about the influences of environmental changes on phytoplankton community in Yellow River Estuary and its adjacent area.A total of 53 species (including 13 undetermined species) which belong to 29 genera of 5 phyla were identified in Jul. 2009. Bacillariophyta and Pyrrophyta accounted for 81.1% and 11.3% respectively. The phytoplankton concentrated in the northern and southern near shore area of the estuary with average cell abundance of 21.23×104 cells/m3. The diatom and dinoflagellate took 40.9% and 6.0% in total cell abundance respectively. In Sep. 2010, a total of 77 species (including 14 undetermined species) which belong to 44 genera of 5 phyla were identified. Bacillariophyta and Pyrrophyta accounted for 87.0% and 11.7% respectively. The phytoplankton concentrated in the northwestern, southwestern near shore area of the estuary and the eastern waters with average cell abundance of 17.03×104 cells/L. The diatom and dinoflagellate took a percentage of 82.6% and 15.2% in total cell abundance respectively. In these two cruises, diatom played a dominant role both in species number and cell abundance. There were fresh water and brackish water species of phytoplankton in the study area, especially in Jul. 2009, abundant freshwater phytoplankton belonged to Cyanophyta occured because of the influence of the ninth water regulation of Yellow River.In Jul. 2009, the main dominant species were Nostocaceae, Actinocyclus octonarius, Thalassionema frauenfeldii, Chaetoceros castracanei and so on. The dominant species were Chaetoceros debilis, Ceratium furca and Eucampia zodiacus in Sep. 2010. For dominant species, there was significant difference between the distribution of carbon biomass and cell abundance and the species with large cell size dominated the distribution trend of carbon biomass.There was a significant negative correlation between phytoplankton abundance and phosphate (R=-0.488,P<0.01) in Sep. 2010. Also, a negative relationship between abundance and silicate was found (R=-0.402,P<0.05). These results indicated that phytoplankton in the study area was limited by this two kinds of nutrients. In this cruise, microphytoplankton and nanophytoplankton were major contributors to the total Chl. a. Near the area of estuary, microphytoplankton made more contribution to the total Chl. a, while nanophytoplankton contributed a higher percentage of the total Chl. a in the southwestern area.