The Primary Study On Residual Flux Of Silicate And Particualte Biogenic Silica In The Changjiang Estuary

The thesis mainly focus on the two important parts of silica cycle in the Changjiang estuary and its adjacent sea.:the particulate biogenic silica and the residual flux of silicate.In the first part,2-4 stations of XuLiuJin were settled for continuous observation during spring tide of every month.PBSi,DSi,DIN,DIP,SPM,POC%,PN%and Chla were determined and the relativity between the parameters are also discussed.In the second part,the three cruises were carried out in the Yangtze Estuary and its adjacent sea in summer,autumn and spring.There were 49 stations for underway observation and 12 anchor stations for continuous observation.Residual fluxes of DSi were calculated using data of flow rate,flow direction,salinity and concentration of silicate.The seasonal variation and within-tide variation of PBSi is similar to SPM,POC%and PN%.The linear relationships between PBSi in surface layer,middle layer and bottom layer of water column and POC%are good.Especially,the linear relationship between PBSi in surface layer and POC%is best.From the sectional view of distribution of PBSi in September,PBSi is less in the deep water.The average concentrations of the Buoy 2# and 4# are 0.826μmol/L and 0.796μmol/L in April,0.865μmol/L and 0.752μmol/L in July,1.138μmol/L and 1.968μmol/L in September respectively.The general tendency is autumn＞summer＞spring and flood season＞dry season.The maximum concentration of PBSi in the area is 2.36μmol/L and the average is 0.82μmol/L.The linear relationships between PBSi and DIP,DIN,DSI are not so good.Probably, there are two reasons.One is that the water column is under light limitation condition and because of high turbidity.Meanwhile,the phosphate limitation effects on the PBSi indirectly.The C/N mole ratio is about 4.654～17.915 in XuLiuJin,and the average is 8.396, which is a little more than 6 of the C/N mole ratio in plankton.The ratio of PBSi/POC is about 0.01～0.02,which is the same with the ratio of pure diatoms.The results of residual fluxes of DSi show as following Compared with vector component of residual fluxes of DSi,values of vector components during spring tide are higher than during neap tide,values at surface are higher than at bottom.The residual fluxes at surface are generally eastward,southeastward or southward,but at bottom are generally westward.The fluxes near the river mouth are higher than far away from there.