Spatial Distribution of Fe, Cu, Mn in the Surface Water System and Their Effects on Wetland Vegetation in the Pearl River Estuary of China

Environmental contextEstuaries play an important role in global carbon cycling in terms of transforming dissolved organic matter (DOM). We describe the molecular composition and spatial distribution of DOM in the Pearl River Estuary, an area severely impacted by anthropogenic activities, and show how DOM composition gradually changes with salinity. The results will help our understanding of the sources and transformations of anthropogenic DOM discharged to the coastal seas. AbstractThe Pearl River is the second-largest river in China in terms of water discharge and brings enormous amounts of nutrients and terrestrial organic matter to the South China Sea, which makes the Pearl River Estuary (PRE) highly eutrophic. However, the molecular composition and distribution of dissolved organic matter (DOM) in the PRE have scarcely been investigated. In this study, solid-phase extraction (SPE) was performed to collect DOM samples from PRE along a salinity gradient. The samples were characterised by negative-ion electrospray ionisation (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to analyse their molecular composition and spatial distribution. The FT-ICR MS results showed that the terrestrial organic matter was gradually diluted and/or degraded during the migration from the river to the coastal ocean. Furthermore, both sulfur containing and unsaturated molecules were highly abundant in the upper stream samples, which indicated that anthropogenic input might be another important source of the assigned DOM in PRE. A group of bio-refractory molecules, characterised as carboxylic-rich alicyclic-like molecules, was found to accumulate with the increase of salinity. The composition of the SPE-DOM showed a gradual variation with the salinity and spatial changes; however, the variation was slightly different from those in pristine estuaries. This study demonstrates that the molecular composition of DOM is crucial for elucidating its source and transformation in an estuary.

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Numerical Investigation of Fresh and Salt Water Distribution in the Pearl River Estuary During a Typhoon Using a Fully Coupled Atmosphere-Wave-Ocean Model

Water ◽

10.3390/w11040646 ◽

2019 ◽

Vol 11 (4) ◽

pp. 646 ◽

Cited By ~ 1

Author(s):

Jie Chen ◽

Changbo Jiang ◽

Zhiyuan Wu ◽

Yuannan Long ◽

Bin Deng ◽

...

Keyword(s):

Surface Water ◽

River Estuary ◽

Pearl River Estuary ◽

Ocean Model ◽

Sea Surface ◽

Pearl River ◽

The Pearl River Estuary ◽

Roms Model ◽

The Pearl River ◽

Fully Coupled

Typhoons are major marine dynamic disasters that affect the coastal ocean areas of China. During a typhoon, the coupling dynamic factors, such as wind, waves, storm surges, and river runoff, greatly enhance the mass and energy exchange at the various interfaces of the ocean. A fully coupled atmosphere-wave-ocean model in the South China Sea (SCS) was established based on the WRF, SWAN, and ROMS models. The variation of sea surface salinity (SSS) and ocean subsurface salinity caused by Typhoon Kai-tak (201213) was analyzed by the fully coupled model, and the basic characteristics of the response of the upper ocean to the typhoon are given in this paper. The simulation results demonstrate that the salinity of the sea surface showed a sharp change during Typhoon Kai-tak, and it changed gradually after entering the recovery period. During the passage of Typhoon Kai-tak, the disturbance caused by strong winds strengthened the mixing process of the water in the Pearl River Estuary (PRE) and its adjacent waters. As the typhoon developed, under the influence of Ekman pumping, the mixing effect between the subsurface and the bottom and the upper water was obvious. Before the impact of Typhoon Kai-tak, the salinity had obvious stratification characteristics along the water depth. Due to the influence of the storm surge, the surface water with increased salinity was transported to the estuary, which led to an increase in the salinity of the estuary’s surface water. In this condition, it is highly likely for there to be saltwater intrusion. The salinity distribution characteristics of three schemes (ROMS model only, coupled WRF-ROMS model, and fully coupled WRF-SWAN-ROMS model) were compared in this study. In the fully coupled WRF-SWAN-ROMS model, the disturbance of the bottom water was the most obvious, and the salinity value was greater than that of the coupled WRF-ROMS model, which indicates that under the influence of waves, the mixing and exchange abilities were strengthened.

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