Temporal And Spatial Variations Of Phytoplankton Community In Response To The Water-sediment Regulation Event In The Adjacent Sea Of The Yellow River Estuary

Estuaries are the intermediate zone which are the connection of terrestrial and ocean ecosystem.With the construction of dams and reservoir in the up-and middle stream of the river,the amount of sediment that flow into ocean was decreased sharply which would bring about significant influence on the estuary ecosystem.The present investigations were performed in Yellow River estuary at April,June,July and September 2013,and in Laizhou Bay at May and September 2014 along with water and sediment regulation event(WSRE).The temperature,salinity,nutrients,chlorophyll a and the structure of phytoplankton community were analyzed and compared variations of environmental factors and phytoplankton community before and after WSRE.The results could provide the basic information for understanding the mechanisms of phytoplankton response and ecological impact of the event.The results showed that before WSRE(in April),the average values of temperature and salinity were 8.01 °C and 26.2,with higher temperature and lower salinity appeared the northern estuary.The analyzing of nutrient structure indicated that there was no dissloved inorganic nitrogen(DIN)limitation but occurred dissloved inorganic phosphorus(DIP)and dissloved silicate(DSi)limitation.After WSRE(June,July andSeptember),the highest average temperature(25.2 °C)and salinity(20.8)appeared in July.The lower values of salinity appeared inshore of the estuary.There was no DIN limitation but occurred DIP limitation,and DSi limitation only emerged in the northwest part of estuary in June.By analyzing the variations of phytoplankton community,42 species of phytoplankton were identified and Paralia sulcata was emerged as dominant species before WSRE;the total cell abundance was 1.65 × 105 cells/L and distributed evenly;the average of Shanno-Wiener index(H?)was 1.14 and higher value appeared in northwest of estuary;the average concentration of chlorophyll a was 2.98 ?g/L and higher value appeared in southwest of estuary.After WSRE,95,100 and 56 species of phytoplankton were identified in June,July and September,respectively;the green algae were emerged as dominant species due to the low salinity at June and July while the dominant species was diatom at September.The highest total cells abundance was 27.0 × 105 cells/L in June and the highest value distributed in north area of Yellow River estuary at June;the highest value of total cell abundance of July distributed in southeast area while the total cell abundance of September was lower than April and distributed evenly.The July with highest H? and higher value emerged in the north area of the estuary whereas higher value of H? of June and September distributed in the east,and east and north part of estuary.The highest value of chlorophyll a was 15.5 ?g/L and appeared at September,and higher value existed at the northwest and southeast part of the estuary.The results of Canonical Correspondence Analysis between phytoplankton assemblages and environmental factors indicated that temperature,DIN,and DIP were the dominant factors which affect the structure of phytoplankton community before WSRE but salinity,DSi,and DIP were the factors after WSRE.Comparing the temporal variation of environmental factors and the structure of phytoplankton before WSRE with after WSRE,the salinity was obviously decreased after WSRE and DSi limitation was alleviated,and the abundance of phytoplankton was increased;among the phytoplankton,the abundance of freshwater species increased as the result of declination of salinity,then weaken the competitive advantage of diatom;thus the percentage of diatom in the composition of species decreased 30%.The survey was carried out in Laizhou Bay in order to further explore the impact of WSRE.The results showed that before WSRE(in May),the average value of temperature and salinity were 14.8 °C and 27.9,with lower salinity appeared seawater which between estuaries of Yellow River and Xiaoqing River.The analyzing of nutrient structure indicated that there was no DIN limitation and only one site with DIP limitation,while up to 80% sites showed DSi limitation.After WSRE(in September),the average value of temperature and salinity were 25.8 °C and 28.7,with lower salinity appeared seawater the same with before WSRE.The analyzing of nutrient structure indicated that there was no DIN limitation and 86.7% of the sites had DIP limitation,but only one site had DSi limitation.By analyzing the variations of phytoplankton community,86 species were identified and Navicula sp.was emerged as dominant species before WSRE;the total cell abundance was 1.80 × 105 cells/L with high value distributed in middle and bottom of the lay;the average of H? was 2.47 and higher value appeared in the mouth of lay;the average concentration of chlorophyll a was 4.62 ?g/L and higher value appeared in Xiaoqing River estuary.After WSRE,112 species were identified and the dominant species belong to diatoms while there was not higher dominance index;the total cell abundance was 3.40 × 105 cells/L with high value distributed inshore;the average of H? was 3.28 and higher value appeared in seawater which between estuaries of Yellow River and Xiaoqing River;the average concentration of chlorophyll a was 4.35 ?g/L and higher value appeared in estuaries of Bailang River and Jiaolai River.The results of Canonical Correspondence Analysis between phytoplankton assemblages and environmental factors indicated that temperature,DIN,and DIP were the dominant factors which affect the structure of phytoplankton community before WSRE but DSi,and DIP were the factors after WSRE.Comparing the temporal variation of environmental factors and the structure of phytoplankton before WSRE with after WSRE,the salinity was not changed obviously and DSi limitation was alleviated which might be result in increasing the abundance and biomass of phytoplankton.In conclusion,WSRE could affect the Yellow River estuary and Laizhou Bay.The WSRE was likely affect the zone from the northwest of the Yellow River estuary to the bottom of Laizhou Bay in spatial,and the influence might last until September in temporal.