THE GEOCHEMISTRY OF BIOGENIC SILICA IN SEDIMENT OF DONGTAN INTERTIDAL FLAT IN CHANGJIANG(YANGTZE) RIVER ESTUARY
GAO Lei1,2,LI Dao-Ji2,YU Li-Hua2,KONG Ding-Jiang2,WANG Yan-Ming2 (1. State Key Laboratory of Marine Geology,Tongji University,Shanghai,200092;2. State Key Laboratory of Estuarine and Coastal Research,East China Normal University,Shanghai,200062)
Biogenic silica(BSi) was determined in two sediment columns in Dongtan intertidal flat in Chang-jiang(Yangtze) River estuary. Due to abundant terrestrial material inputs that cause a clay effect,sequential ex-traction was carried out in BSi measurement. Results indicate that,similar to the sediments in the Bohai Sea and the Yellow Sea,BSi content in Dongtan sediments was relatively lower( 0.5Si%) ,than those of other regions of the world. The high clay content of the sediment decreased the solubility;and the highest SiO32? concentrations in the porewater was no more than 250 μmol/L,much lower than the solubility greater than 1000 μmol/L in pure opal in similar environmental conditions. A consistent tendency was found that particulate N(%) and all molar ratio of N/BSi(mol/mol) decreased with depth,which might reflected the decomposition of N and BSi in early diagenesis process and that element N was of higher decomposition rate than BSi. The positive relationship be-tween δ15N(‰) and N or N/BSi revealed in the study suggests that 15N was released more readily from the organic matter than 14N did. Moreover,the sedimentation was greatly influenced by events such as typhoon,artificial dam,and so on,which has been demonstrated by the irregular data found in the profiles.