The Geochemical Index Study On Biogenic Elements Of Silica And Carbon In Marine Sediments

The concentration of biogenic silica in the core sediment could reflect the growth status of planktonic diatom. The biogenic silica and total organic carbon(TOC) deposited after the death of phytoplankton, they could reflect the changes of primary productivity of water body in different stage. But in the coastal zone, the source of TOC will be complicated because of the terrestrial input and the impact of human activities. In this study, we investigate the biogenic silica and TOC from core sediment in three different bays(Shenzhen bay, Zhangjiang Bay, Liusha Bay), to study the change of planktonic diatom and primary productivity in different stages and the respond to weather. To discuss the source of TOC in different sea and the variation tendency of carbon input in Marine ecosystem under different human activities impact. Which can provide scientific basis and guidance to reasonably develop marine resources, protect the marine ecology, and coordinated development of economy and environment. The maid conclusions are as following in this study:1): In Shenzhen Bay, TOC was produced by marine phytoplankton in the sediment 290-30 cm, but terrigenous organic carbon and marine microorganism were the mainly contributors in the sediment 90-0 cm. In Zhanjiang Bay, TOC mainly derived from the deposition of phytoplankton, bacterium and terrigenous advanced plants. In Liusha Bay, the marine phytoplankton were the principal origin of TOC.2): The reason of biogenic silica indicated primary productivity was different in the marine ecosystem because of the different carbon input from terrestrial sources.The biogenic silica come from the marine planktonic diatoms sediment, which could indicate the primary productivity of water at that time. The primary productivity in Shenzhen Bay sustained to decline in the sediment 290-170 cm(1890s-1940s), then increased quickly in the sediment 170-110 cm(1940s-1960s) and stayed at the higer level, and declined again to the lower level in the sediment 110-65 cm(1960s-1980s). It is the weather that caused the fluctuation of primary productivity in the sediment 290-65 cm because of the less carbon input from terrestrial sources. But the the effect of nutrition was more obvious in the sediment 65-0 cm for the influence of terrestrial input. Being caused by the nutrition, the primary productivity of marine in Zhanjiang Bay increase rapidly in the sediment 65-50 cm and down gradually in the sediment 50-0 cm. there is no obvious fluctuation of biogenic silica in core sediment, which sugest that the primary productivity of marine in Liusha Bay was stable.3): In Shenzhen Bay, TOC was produced by marine phytoplankton in the sediment 290-30 cm, but terrigenous organic carbon and marine microorganism were the mainly contributors in the sediment 90-0 cm. In Zhanjiang Bay, TOC mainly derived from the deposition of phytoplankton, bacterium and terrigenous advanced plants. In Liusha Bay, the marine phytoplankton were the principal origin of TOC, but the terrigenous organic carbon were less.4): The large number of terrigenous organic carbon imput made great influence to TOC indicated marin primary productivity. In Shenzhen Bay, the content of TOC and biogenic silica showed positive correlation in the sediment 290-90 cm for less terrigenous organic carbon imput, but there is no relationship in 90-0 cm. In Zhanjiang Bay, the content of TOC and biogenic silica was also positive correlation, but in Liusha Bay, the relationship between them were lower. In a word, using both TOC and biogenic silica as indicators can accurately refelect marine primary productivity.5): In the bay ecological system, carbon input from anthropogenic activities was corresponded to the economic development level. In Shenzhen Bay,the carbon input from human activity was apparently higher than Zhanjiang Bay and Liusha Bay with the rapid development of economy in recent 20 years. Liusha Bay was surrounded by villiages with the lowest carbon input from human activities, though zhangjiang bay and Liusha Bay were in Zhangjiang area.