Research On The Impact Of The Water-sediment Regulation On Phytoplankton Assemblages And The Environment In The Adjacent Sea Of The Yellow River Mouth

This paper made two surveys on June, 2013(the early stage of the 16 th water-sediment regulation) and July, 2013(the later stage of the16 th water-sediment regulation) in the adjacent sea of the Yellow River mouth. The concentrations of Chlorophyll a and nutrients were measured and phytoplankton species were identified in the laboratory. Biological factors of phytoplankton community structure, including phytoplankton diversity index(H’), evenness index(J), phytoplankton cell abundance were analyzed. Combined with the temperature and salinity data measured on site, the response characteristics of phytoplankton assemblages and the environment in the adjacent sea of the Yellow River mouth to the water-sediment regulation were studied.During the early stage of the 16 th water-sediment regulation, the salinity and DIP(Dissolved Inorganic Phosphate) concentrations were strongly influenced by the input of freshwater in the adjacent sea of the Yellow River mouth. In comparison, the influence on temperature, the concentrations of DIN(Dissolved Inorganic Nitrogen) and DSi(Dissolved Inorganic Silicate) were not very obvious, which only reflected near the entrance. The analysis on nutrients concentrations and structure indicated that there was no DIN limitation, and DIP has an absolute and relative limitation, while DSi limitation only appeared in a few sites. The concentrations of Chlorophyll a and nutrients have a similar spatial distribution. The biomass proportion of Chlorophyceae was the highest in the transections of A, B, F; Dinoflagellates, especially Prorocentrum minimum were dominant in the transection of C; the biomass proportions of Dinoflagellates decreased significantly, while Chlorophyceae and Diatoms were both high in the transections of D and E.During the later stage of the 16 th water-sediment regulation, the result showed that temperature, salinity and nutrients concentrations were strongly influenced by the input of freshwater in the adjacent sea of the Yellow River mouth. The analysis on nutrients concentrations and structure indicated that there was no DIN and DSi limitations, DIP had an absolute and relative limitation. The concentrations of Chlorophyll a and nutrients presented a similar spatial distribution. Diatoms and Dinoflagellates in the transections of A, B, F were dominant.While the biomass proportions of Cyanophyceae and Chlorophyceae increased distinctly in the transections of C, D and E.Based on the research of changing process of phytoplankton assemblages and environmental factors during the water-sediment regulation in 2013, some results can be summarized as below.The change of environmental factors: Temperature, salinity, nutrients concentrations and nutrients structure changed dramatically during the water-sediment regulation. Compared to the environmental factors during the early stage of the water-sediment regulation, water temperature rose during the later stage of the 16 th water-sediment regulation, salinity decreased by 15.8%; DSi concentration increased by nearly three times from 10 μmol/L to 39.6 μmol/L, DIN concentration increased by 35.9% from 30.6 μmol/L to 41.6 μmol/L, DIP concentration increased by 50% from 0.06 μmol/L to 0.09 μmol/L; DIN/DIP decreased by 54.6%, DSi/DIP increased by 43.7%, DSi/DIN increased by two times. The absolute and relative limitation of DSi disappeared, and the absolute limitation of DIP was alleviated to a certain level, while relative limitation of DIP increased. The spatial distribution features of temperature, salinity and nutrients reflected the effect degree of the water-sediment regulation.The change of phytoplankton assemblages: The phytoplankton assemblages changed dramatically during the water-sediment regulation. Shannon-Wiener indices and Pielou’s Evenness indices during the later stage of the water-sediment regulation were higher than those during the early stage of the water-sediment regulation. It proved that the water-sediment regulation can improve the stability of the ecological system in the adjacent sea of the Yellow River mouth.Chlorophyll a concentration doubled; the biomass proportions of Chlorophyceae and Dinoflagellates decreased, while the biomass proportions of Diatoms and Cyanophyceae increased during the later stage of the water-sediment regulation. It showed that the phytoplankton biomass and the assemblage structure had changed, due to the influence of the water-sediment regulation.