Process-oriented study of the circulation and river plume in the Pearl River Estuary: Response to the wind and tidal forcing

A three-dimensional, primitive equation numerical model is utilized to study the responses of the river plume and estuarine circulation to the wind and tidal forcing in an idealized Pearl River Estuary (PRE) with simplified geometry and physical forcing. This process-oriented study shows that without any other physical forcing, the buoyant-driven circulation, under the Earth rotation effect, forms an anticyclonic eddy in a funneled estuary with a concave bathymetry. However, this eddy disappears with additional wind or tidal forcing. The movement of the buoyant plume is retarded, and the thickness of the plume is largely increased by the tidal forcing as a result of the great enhancement of the vertical mixing inside the estuary and around the mouth of the estuary on the shelf. On the other hand, with wind forcing, the plume moves faster along the seaward branch of the wind-induced estuarine circulation with a narrower width confined by the current. And the wind-induced circulation increases the intrusion of the oceanic saltier water into the estuary, especially in upwelling case, and the consequently enhanced stratification along the axis of the estuary reduces the vertical mixing and the thickness of the plume. The study reveals the interactive roles of the buoyant plume, tidal, and wind forcing on the circulation in the estuary and adjacent shelf waters

On the role of wind and tide in generating variability of Pearl River plume during summer in a coupled wide estuary and shelf system

A numerical simulation of the buoyant river plume over the Pearl River Estuary (PRE) and adjacent shelf during a typical upwelling favorable wind period of the summer monsoon is utilized to explore the responses of the plume to wind and tide forcing. The model is forced with time-dependent river discharge, wind and tide, and it shows reasonable ability to capture the basic structure and responses of the plume. Additional numerical experiments that are forced without either wind or tide are used to evaluate the relative importance of wind and tide in generating plume variability. Results show that the vertical structure of the plume and the strength of the stratification in the estuary are determined by the combination of the buoyancy forcing associated with river discharge and tidal forcing, and vary with the advection process, while the horizontal shape and spreading of the plume over the shelf are highly influenced by the wind-driven coastal current, and are more susceptible to the change of vertical mixing. Mechanical energy analysis in each dynamical region (upper, middle, lower estuary, and shelf) reveals that this is because the system mainly gains energy from tide (wind) in the estuary (shelf), and loses energy to the bottom friction (internal-shear mixing) in the estuary (shelf). The largest forcing and dissipation terms in the middle PRE, and at the entrances of smaller estuaries such as Huang Mao Hai, are due to tidal forcing, which enables the middle PRE to serve dynamically as the entrance of an estuary, where the transition of the river plume into coastal buoyancy current usually takes place. In addition, the mixing efficiency increases from upper PRE to the shelf and from strong to weak mixing period, thus the plume in the well-mixed upper estuary is not as sensitive to the changes of wind and tide as that over the highly stratified shelf. (C) 2014 Elsevier B.V. All rights reserved

Biomimetic mercury immobilization by selenium functionalized polyphenylene sulfide fabric

Abstract Highly efficient decontamination of elemental mercury (Hg0) remains an enormous challenge for public health and ecosystem protection. The artificial conversion of Hg0 into mercury chalcogenides could achieve Hg0 detoxification and close the global mercury cycle. Herein, taking inspiration from the bio-detoxification of mercury, in which selenium preferentially converts mercury from sulfoproteins to HgSe, we propose a biomimetic approach to enhance the conversion of Hg0 into mercury chalcogenides. In this proof-of-concept design, we use sulfur-rich polyphenylene sulfide (PPS) as the Hg0 transporter. The relatively stable, sulfur-linked aromatic rings result in weak adsorption of Hg0 on the PPS rather than the formation of metastable HgS. The weakly adsorbed mercury subsequently migrates to the adjacent selenium sites for permanent immobilization. The sulfur-selenium pair affords an unprecedented Hg0 adsorption capacity and uptake rate of 1621.9 mg g−1 and 1005.6 μg g−1 min−1, respectively, which are the highest recorded values among various benchmark materials. This work presents an intriguing concept for preparing Hg0 adsorbents and could pave the way for the biomimetic remediation of diverse pollutants