Marine Ecological Disasters and Their Physical Controlling Mechanisms in Jiangsu Coastal Area

The studies in this chapter are focused on marine ecological disasters in Jiangsu coastal area. Three kinds of algal blooms occurred in this region, namely, red tide associated with Dinoflagellate, green tide associated with Ulvaprolifera and golden tide associated with Sargassum. Numerical model results demonstrated that red tides in Haizhou Bay originated locally, because most of Dinoflagellates near Zhoushan Islands would be transported northeastward by the Changjiang diluted water, and even the lucky ones that entered the south of Jiangsu coastal area would die in the Subei Shoal due to high turbidity there. Due to the Changjiang diluted water and the prevailing southerly wind, Ulvaprolifera could not drift southward, either. Seawater with high turbidity in the Subei Shoal limited sunlight penetration into deep water column, and further inhibited the growth of Ulvaprolifera suspending in the water column. In this chapter, we use drift bottles and satellite-tracked Argos drifters to provide solid direct dynamic evidence that Ulvaprolifera could drift from the Subei Shoal to Qingdao coastal area and even further north. The sand ridges limited the traveling path of Ulvaprolifera in the Subei Shoal, and wind-driven currents and other baroclinic processes helped Ulvaprolifera travel farther to the north

Transport and deposition of high-concentration suspensions of cohesive sediment in a macrotidal estuary

A width-averaged two-dimensional (2-D) model and a three-dimensional (3-D) model have been developed for the Jiaojiang estuary which is a highly turbid and macrotidal estuary. The sediment-induced buoyancy effects and the consequent turbulence damping effects have been taken into account in these models. It is possible to consider the upper suspensions and fluid mud as a whole, without empirical exchanges between these two compartments, as in the so-called continuous approach. The Princeton ocean model (POM) with a generalized sigma-coordinate system has been used as the hydrodynamics module of the 3-D model with improvements on advection schemes for scalar variables, introducing the drying and flooding algorithm and the additional capacity to deal with the non-Newtonian effects of high-concentration mud suspensions. Simultaneous currents and SSC (Suspended Sediment Concentration) time series data from several elevations at a mooring site and from ship-born observations over a tidal cycle in April 1991 enable the calibrations of these models. From the simulations and observations, some important findings have been obtained. The effective hydrodynamic drag is reduced in the very turbid environment. Under conditions of strong stratification due to sediment, the overall hydraulic roughness will be further decreased. The total mass of suspended sediment in the estuary is around 1.2x106 tons. The asymmetry in tidal currents drives the outer sediment to enter the estuary during the simulated period. The magnitude and location of turbidity maximum vary in the tidal cycle. The SSC, salinity and current have obvious longitudinal variations, while they also have cross-channel variations. The lutocline almost occurs over the entire cycle except during the period around high water slack. The fluid mud generally concentrates in the deep portions of estuary and in the shallow zone separating the estuary and Taizhou Bay

Modelling nitrogen and phosphorus cycles and dissolved oxygen in the Zhujiang Estuary. II. Model results

In the present study, the ecosystem-based water quality model was applied to the Pearl River (Zhujiang) Estuary. The model results successfully represent the distribution trend of nutrients and dissolved oxygen both in the horizontal and vertical planes during the flood season, and it shows that the model has taken into consideration the key part of the dynamical, chemical and biological processes existing in the Zhujiang Estuary. The further studies illustrate that nitrogen is in plenty while phosphorus and light limit the phytoplankton biomass in the Zhujiang Estuary during the flood season

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

Modeling nitrogen and phosphorus cycles and dissolved oxygen in the Zhujiang River Estuary, Part I. Model development

An ecosystem based water quality model was designed to estimate the biochemical reaction of nutrient and dissolved oxygen in conjunction with a three-dimensional hydrodynamics and sediment model. As both phosphorus and nitrogen successively limit phytoplankton growth in many estuaries, the model simulates both these nutrient cycles using five variables, namely, dissolved inorganic nutrient, detritic organic matter, benthic matter, phytoplankton and zooplankton

Modelling nitrogen and phosphorus cycles and dissolved oxygen in the Zhujiang Estuary I. Model development

An ecosystem-based water quality model was designed to estimate the biochemical reaction of nutrient and dissolved oxygen in conjunction with a three-dimensional hydrodynamic and sediment model. As both phosphorus and nitrogen successively limit phytoplankton growth in many estuaries, the model simulates both these nutrient cycles each using five variables, namely, dissolved inorganic nutrient, detritic organic matter, benthic matter, phytoplankton and Zooplankton