*2.2. Sampling Collection*

Samples from M4-1 (122.13◦ E, 31.04◦ N), M4-8 (122.97◦ E, 31◦ N), and M4-13 (124.01◦ E, 31◦ N) were collected on 26–27 July, 13–14 August, and 14–15 August in 2006 during cruises on the Changjiang River estuary plume (Figure 1). No tropical cyclones, typhoons, or rainstorms occurred during the sampling period [24]. Although the sampling period spanned nearly 17 days because the three stations are regulated by regular semidiel tides, we considered the water properties of each station to be quasisynchronized within almost one month, so each station is representative of a typical summer in a specific location. This is consistent with approaches used by other studies in summer [25–27]. The water depths at each station were 6, 52, and 37 m, respectively. Samples from the surface layer (2 m), depths of 5, 10, 30, and the bottom layer (with a height of 2 m above the seabed) were collected every three hours for 24 hours. In particular, we collected 5 m when the high slack tide impacted the M4-1 station and 4 m otherwise. In this study, M4-1, M4-8, and M4-13 denote the near-shore, front, and o ffshore regions, respectively.

**Figure 1.** Map of Changjiang River estuary plume (**a**) and sampling stations (**b**): stations M4-1, M4-8, and M4-13 denote the near-shore, front, and o ffshore regions, respectively.
