Biogeochemical Cycle of Biogenic Elements

In surface sediments of Bohai, the NH4-N in the Bohai central basin increased from the northeast toward the southwest and there were two abnormally high values in the central region. The NH4-N in Laizhou Bay was distributed uniformly and there were relatively low values in the south of Bohai Bay. Moreover, the values increased toward the north. The NO3-N in the Bohai central basin increased from the east and west sides towards the center, but for Bohai Bay and Laizhou Bay, the NO3-N decreased the further the distance from the shore. Results showed that the adsorbed inorganic nitrogen in 

There are strong nitrification and denitrification in Zhujiang River Estuary sediments and the average nitrification, denitrification, and nitrate reduction rates ranged from 0.32 to 2.43 imnol/(m h), 0.03 to 0.84 mmol/(m h), and 4.17 to 13.06 mmol/(m -h), respectively. The vertical profiles of the sediments showed that the nitrification and denitrification processes mainly took place in the depth from 0 to 4 cm and there were differences at different sampling sites. The rates of nitrification, denitrification, and nitrate reduction were dominated by Eh, nitrate, and ammonium concentrations in sediment and DO in overlying water (Xu et ah, 2005). 

Phosphorus is not only one of the essential components for the growth and breeding of phytoplankton, but also the fundamental element for marine primary productivity and the food chain. Sediment is one of the important sources of phosphorus in seawater moreover, it is a buffer for the phosphorus in overlying water. Therefore, it is of great significance for the dynamic cycle, the transformation at the sediment-seawater interface, and the subsequent digenesis to study phosphorus and its forms. 

The study of the phosphorus adsorption in the Changjiang River Estuary sediments showed that the sediments were buffers to phosphate and the balance time of phosphorus adsorption (desorption) was about 6 h. The saturated adsorption quantity of phosphorus was about 600 pg/g and the saturated desorption was about 126.37 pg/g. The apparent adsorption heat of fine sediments (AH) was 47.59 kJ/mol. The adsorption of phosphate was in accordance with Freundlich s isothermal equilibrium and it was a heat absorption reaction. The contents of sand and mud in sediments had some influence on adsorption and the adsorption would decrease with the increase in sand or mud content. In general, the increase in pH favors adsorption. Moreover, the increase in salinity does not favor adsorption but favors desorption. The research shows that the release of phosphorus in the sediments of the Changjiang River Estuary 

In addition, the research on sediment phosphorus can supply information about the paleoenvironment. The information about the environment and biogeochemistry of phosphorus extracted from the South Sea shelf slope sediments showed that the supply of terrigenous phosphorus for the sea was steady overall. The change in phosphorus contents in different depths was the result of climate and environmental changes. The vertical distribution of phosphorus had an opposite trend to calcium carbonate and Cd in sediment. The ebb and flow between CO2 and in seawater calculated by chemical balance in- 

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