Impacts of River Discharge on the Sea Temperature in Changjiang Estuary and Its Adjacent Sea

Hui Shen,Ye Zhu,Zhiguo He,Li Li,Yingzhong Lou

doi:10.3390/jmse10030343

Abstract

Freshwater plume at the Changjiang River (CR) mouth are essential to the coastal water quality and ecosystem because they can cause estuary stratification and hypoxia, potentially deteriorating the water environment. Furthermore, the advection heat transport is modulated by increasing anthropogenic effects. A comprehensive understanding of the influence of river discharge on the three-dimensional sea temperature, fronts and thermal stratification in the CR estuary remains lacking. A well-calibrated numerical model using Regional Ocean Modeling Systems (ROMS) is used to investigate the impacts of CR discharge on the sea temperature in coastal zones. Model results show that the amplitude and spatial distribution of the heating or cooling rate can be influenced by CR freshwater, especially in frontal areas. Specifically, the large runoff flow will reduce the heating or cooling rate in shallow waters (<20 m) near the CR estuary, whereas it has an opposite effect on the Zhoushan islands region (>20 m). Generally, the effect of the freshwater discharge on the upper layer is greater than on the bottom layer, and the runoff has a positive correlation to the intensity of the frontal zones in the CR estuary, though this relationship is weakened in autumn because of the weak intensity of the frontal zone. Note that seawater thermal stratification and its seasonal variation can be regulated by runoff; thermal stratification will be strengthened in abundant runoff conditions and weakened in scarce runoff conditions.

Highlights

Received: 30 December 2021The Changjiang River (CR) estuary and its adjacent sea is the largest estuary along the coast of the East China Sea (Figure 1)
The north, east and south edges are open boundaries according to the realistic bathymetry, whereas the west boundary is the input of river discharge
We discuss the impact of river discharges on the sea temperature structure in the CR estuary and its adjacent sea

Summary

Introduction

Received: 30 December 2021The Changjiang River (CR) estuary and its adjacent sea is the largest estuary along the coast of the East China Sea (Figure 1). CR, as the third-largest river in the world, is by far one of the most important ways of discharging water and sediment directly into an estuary. The hydrodynamics in the CR estuary and its adjacent sea are influenced by various factors, such as river discharge, atmospheric forcing and tidal mixing. Among these factors, the effect of freshwater has dominated the surface distribution of water properties [1,4]. The Changjiang runoff, which is mixed with inshore seawater and known as the Changjiang diluted water (CDW), is mainly distributed along the Jiangsu and Zhejiang coast adjacent to the Changjiang estuary [5]. The CDW forms a narrow freshwater band along China’s southeast coast; in summer, it extends northeastward toward

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