The study area is mainly influenced by the eastern Taiwan Warm Current system and the western coastal current system (
Sun, 2006). The concentrations of DIN,
${{\rm {PO}}_4^{3-}} $ and
${{\rm {SiO}}_3^{2-}} $ showed a downward trend from near-shore waters to far-shore waters (
Fig. 4), indicating the important influence of coastal current system, especially the diluted water of Changjiang River and Qiantang River (
Chen et al., 2010;
Gao et al., 2011). Two streams of waters flowed out of the two rivers, met outside of the Changjiang River Estuary and west of Zhoushan Islands, and then gradually mixed into the East China Sea. The changes of biogenic elements were analyzed in two sections of the Changjiang River Estuary (31.55°N) and Hangzhou Bay (30.55°N) (
Fig. 6). Results showed that the biogenic elements behaved conservatively in the Changjiang River Estuary, but not in the Hangzhou Bay. Concentrations of biogenic elements (DIN,
${{\rm {PO}}_4^{3-}} $,
${{\rm {SiO}}_3^{2-}} $) remained stable inside the Changjiang River Estuary and then decreased linearly in the East China Sea. A slight decrease of
${{\rm {PO}}_4^{3-}} $ could be seen, perhaps because parts of P were sequestered in sediments of the Changjiang River Estuary (
Yang et al., 2015). While concentrations of biogenic elements inside the Hangzhou Bay fluctuated, due to the open trumpet-shaped topography (
Gao et al., 2011). The concentrations generally decreased inside the estuaries as the space being larger, and the slope was a little smaller than that outside the estuary. While there was a slight increase of
${{\rm {PO}}_4^{3-}} $ from the river up halfway the estuary, likely due to other sources of
${{\rm {PO}}_4^{3-}} $, such as anthropogenic input, organic matter regeneration (
Chen et al., 2010).