Modern sedimentation environments in the coastal zone of East China

Abundant islands and rivers occur in the waters off Zhejiang coast of East China. Huge amount of terrestrial materials carried by the Yangtze River moves to the east by coastal current. It is an area with the most intense land-sea interaction. In the summers of 2016 and 2017, 570 surface sediment samples were collected from the East China Sea, and physical and chemical properties, grain size distributions and organic matter contents of sediments were tested. Results show that sediments in Hangzhou Bay are dominated by clayey silt with high pH (> 7), low Eh (< 0) and low shear strength (< 0.5kPa). The content of organic matters is higher in the north rather than in other regions. Generally, no obvious distribution pattern is observed for those parameters, but they are significant correlated. In the east coast of Zhejiang, for example, the sediments are dominated by silt in the north (Zhoushan-Taizhou), but by mud in the south (Taizhou- Wenzhou). Both pH and Eh are decreasing seaward. Higher content of organic matters have been found in the Xiang-shan Port and Yue-qing Bay. However, there is no significant correlation between different parameters. Therefore, the sedimentary environment of Hangzhou Bay and the eastern Zhejiang coastal area is obviously different. In Hangzhou Bay, the sediment distribution is more regular due to the rather stable sources and strong hydrodynamic environment. However, the sediment sources and hydrodynamic environment vary significantly due to widely distributed islands and rivers to the east coast of Zhejiang.