Distribution of biogenic silica in surface sediments from the shoals in the Yangtze estuary

Distributions of biogenic silica (BSi) in surface sediments from the shoals in the Yangtze Estuary were investigated using an 8-hour sequential extraction method, and the relationships of BSi with the sediment physio-chemical characteristics were also discussed. The findings indicated that the BSi contents in the shoal sediments varied from 0.47% to 1.02%, and the average content was 0.75%. The BSi contents range of the high, middle and low intertidal flats was 0.47%-0.91%, 0.48%-1.02% and 0.47%-0.96%, respectively. The significant positive relationships were found between BSi and the clay and silt contents in sediments, which indicated that the accumulation of BSi in sediments closely depended on sediment compositions. There also existed the remarkable positive relationships between BSi and organic carbon (OC) and nitrogen (ON). This implied that BSi was apt to accumulate in sediments enriched in organic matter. Compared with Redfield ratios, the ratios of OC/BSi and ON/BSi in shoal sediments were relatively lower and in the range of 0.28-2.59 and 0.05-0.21, respectively. Therefore, it was shown that the dissolution rate of BSi in shoal sediments was lower than the rate of organic matter decomposition. In addition, it was also found that there was the weak positive correlation between BSi and chlorophyll in the sediments, reflecting that primary productivity such as diatoms, to some certain, made contribution to the storage of BSi.