Biogenic Silica In Suspended Matter And Sediments In The Yangtze River Estuary And Its Adjacent Sea

Silicate is one of the major nutrient elements for estuarine and coastal ecosystems, whichoften dominate phytoplankton communities and have important roles in diatoms, radiolarian andsilicoflagellate, etc. Biogenic silica, also called Opal, is refers to amorphous silicon detected bychemical methods. Biogenic silica recorded by marine sediment responses the changes of oceanprimary production during the past hundreds or even thousands of years. Thus, silicon cycleresearch has been attracting increasing attention worldwide in the past few years.Aimed at a deep understanding of the distribution characteristics and changing process ofbiogenic silica, two cruises were carried out at June and August2011, respectively, focusing onthe concentrations of dissolved silica, biogenic silica in suspended particle matter and sediments,and physicochemical property of suspended particle matter and sediments. Primary conclusionsare listed as follows:The average content of biogenic silica in suspended matter of the Yangtze River Estuary andits adjacent sea is1.38μmol/L, which is at a middle level when compared with other waters in theworld. The higher value of biogenic silica（μmol/L） is near the Yangtze River mouth door; thefarther offshore, the content is lower. The distribution of biogenic silica（%） is quite differentbetween the surface layer and the bottom layer. The higher value of biogenic silica（%） in surfaceand the bottom layer is located in the Yangtze River mouth door, Zhejiang and Fujian coastalwaters and offshore waters. The lower value of biogenic silica（%） in the surface layer is locatedin the turbidity maximum zone in the Yangtze River Estuary and the southeast of Hangzhou Bay,while the lower value of biogenic silica（%） in the bottom layer is located in the northeast and thesouth of the Hangzhou Bay.Biogenic silica content in sea water is controlled by three factors:（1） sediment resuspensionprocess;（2） production of live diatoms;（3） the dissolution of Biogenic silica. Within the range ofsalinity0-5and25-30,（1） and （2） factors play a major role; within the range of salinity5-25, thedominant factor is （3）. After the maxium value of biogenic silica, diatom biomass and primary productivity levels gradually decreased with the gradual increase of salinity and reducement ofSiO₃^2--Si.The content of biogenic silica in surface sediments is0.41%in June, August2011. The clayminerals and silt sediments are enriched with more biogenic silica. The value of biogenic silicain sediment has a close relationship with the specific surface area. The biogenic silica（%）distribution characteristics had a similar contribution with TOC, TN in the surface sediments ofthe Yangtze River Estuary and adjacent seas. The biogenic silica（%） in the surface sediments isdiluted by the biogenic silica（%） in the suspended matters. The biogenic silica deposition flux issignificantly higher than the SiO₃^2--Si flux, and the Yangtze River Estuary and adjacent watersmay be the sink of biogenic silica.The mean value of biogenic silica in the Core Sediments is in the range of0.31-0.52%. Thedistribution characteristic of biogenic silica values in core sediments is that: the mud area insoutheast of Hangzhou Bay mouth> the non-mud area in the southeast of survey area> the mudarea of Zhejiang and Fujian coast. The explanation of this phenomenon may be that theresuspension process is strong, and silicon cycle is fast, which result in biogenic silica is too lateto save in the mud area of Zhejiang and Fujian coast.