Recent Spatio-Temporal Variations of Suspended Sediment Concentrations in the Yangtze Estuary

Haifei Yang,Yuting Liu,Bochang Li,Junfang Bi,Fengnian Zhou,Chaoyang Zhang,Zhilin Zhang,Hongjie Qiao

doi:10.3390/w12030818

Abstract

Water and sediment are two of the most essential elements in estuaries. Their product, suspended sediment concentration (SSC), is involved in hydrology, geomorphology and ecology. This study was focused on the spatial and temporal variations of SSC in the Yangtze Estuary under new situations after the closure of ~50,000 dams in the Yangtze basin, including the Three Gorges Dam (TGD) in 2003. It was found that the SSC first exhibited an increasing and then a decreasing trend longitudinally from Xuliujing Station to the outer estuary with the Turbidity Maximum Zone located in the mouth bar area. Vertically, the SSC in the bottom layers averaged 0.96 kg/m3, about 2.4 times larger than the surface layers (0.40 kg/m3). During spring tides, the SSCs were always higher than those in neap tides, which was fit for the cognition law. As for the seasonal variations in the North Branch and mouth bar area, the SSCs in the dry season were higher than those in the flood season, while in the upper reach of the South Branch and outer estuary, the seasonal variation of SSCs reversed. This phenomenon primarily reflected the competition of riverine sediment flux and local resuspended sediment flux by wind-induced waves. As for the interannual changes, the SSCs demonstrated overall fluctuant downward trends, determined by riverine sediment flux and influenced by waves. This study revealed the new situation of SSC and can be a reference for other related researches in the Yangtze Estuary.

Highlights

Rivers are the lifeblood of human civilization and still play critical roles in human daily life.It attracts many studies in all kinds of aspects, such as hydrology, geomorphology, environments, ecology etc. [1,2,3,4,5,6]
In the tidal-cycle scale, net erosion/accretion relies on the competition between erosion flux and deposition flux, and deposition flux is positively correlated with suspended sediment concentration (SSC) [11,12,13]
The maximum of SSC in the Yangtze Estuary was found as 2.15 kg/m in the middle reach of the North maximum of SSC in the Yangtze Estuary was found as 2.15 kg/m33in the middle reach of the North

Summary

Introduction

Rivers are the lifeblood of human civilization and still play critical roles in human daily life.It attracts many studies in all kinds of aspects, such as hydrology, geomorphology, environments, ecology etc. [1,2,3,4,5,6]. Rivers are the lifeblood of human civilization and still play critical roles in human daily life. It attracts many studies in all kinds of aspects, such as hydrology, geomorphology, environments, ecology etc. Of all the riverine discharges, sediment and water are two of the most basic elements They are two necessary observation parameters in modern estuarine and coastal research. Their product, suspended sediment concentration (SSC), is a key factor influencing the nutrient concentration, the illumination intensity and the growth of phytoplankton in the water [5,7,8,9,10]. In the tidal-cycle scale, net erosion/accretion relies on the competition between erosion flux and deposition flux, and deposition flux is positively correlated with SSC [11,12,13]

Methods

Results

Conclusion