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This study focuses on mechanisms of shelf valley bathymetry affecting the spread of riverine freshwater in the nearshore region. In the context of Changjiang River, a numerical model is used with different no-tide idealized configurations to simulate development of unforced river plumes over a sloping bottom, with and without a shelf valley off the estuary mouth. All simulated freshwater plumes are surface-trapped with continuously growing bulges near the estuary mouth and narrow coastal currents downstream. The simulations indicate that a shelf valley tends to compress the bulge along the direction of the valley long axis and modify the incident angle of the bulge flow impinging toward the coast, which then affects the strength of the coastal current. The bulge compression results from geostrophic adjustment and isobath-following tendency of the depth-averaged flow in the bulge region. Generally, the resulting change in the direction of the bulge impinging flow enhances down-shelf momentum advection and freshwater delivery into the coastal current. Sensitivity simulations with altered river discharges Q, Coriolis parameter, shelf bottom slope, valley geometry, and ambient stratification show that enhancement of down-shelf freshwater transport in the coastal current, ΔQc, increases with increasing valley depth within the bulge region and decreasing slope Burger number of the ambient shelf. Assuming potential vorticity conservation, a scaling formula of ΔQc/Q is developed, and it agrees well with results of the sensitivity simulations. Mechanisms of valley influences on unforced river plumes revealed here will help future studies of topographic influence on river plumes under more realistic conditions.

The aim of the current paper is to investigate hydrodynamic characteristics of the artificial upwelling induced by ocean currents. Experiments were performed in a flume at different density difference heads, horizontal current velocities and upwelling pipe diameters. A three-dimensional computational fluid dynamics (CFD) model was employed on wider range of parameters for further analysis. The performance of the numerical model has been confirmed by the experimental findings. The present results show that the volume flow rate of current-induced artificial upwelling is influenced by geometrical parameters and inclination angle of the pipe, the horizontal current velocity and vertical distribution of water density. In ideal two-layer density stratified water, the critical current velocity to generate upwelling linearly increases with the increase of the density difference, and the maximum rising height for upwelling is inversely proportional to the density difference. Feasibility analysis was taken by using current and density profiles of the East China Sea near Dongji Islands, which provides an useful reference for engineering practice.

Artificial downwelling potentially counteracts severe eutrophication and hypoxia in coastal regions. The entrainment that commonly occurs in the downwelling-induced plume can develop around a compensatory downward flow at a scale of kilometers, which favors below-pycnocline ventilation and thus mitigates hypoxia in bottom water. However, little discussion has been made on the entrainment of artificial downwelling. The paper focus on the total entrained (TE) flow rate that represents the magnitude of entrainment transport. Injection of a negatively buoyant jet from a round pipe into a stagnant and homogeneous ambient medium is numerically studied using a verified standard k- e turbulence model, in which different initial pipe flow speeds, density differences and pipe radii are involved. Previous theories and experiments confirm the numerical model. An empirical formula is fitted to the simulation data to calculate the TE flow rate, which permit quantitative analysis of the capacity of ventilation for artificial downwelling. The efficiency index of ventilation (EIV) is also defined and applied to study a typical downwelling device, i.e., a tidal pump, to suggest optimal engineering parameters.

Hypoxia is becoming a serious problem in coastal waters in many parts of the world. Artificial downwelling, which is one of the geoengineering-based adaptation options, was suggested as an effective means of mitigating hypoxia in coastal waters. Artificial downwelling powered by green energy, such as solar, wind, wave, or tidal energy, can develop a compensatory downward flow on a kilometer scale, which favors below-pycnocline ventilation and thus mitigates hypoxia in bottom water. In this paper, we review and assess the technical, numerical, and experimental aspects of artificial downwelling all over the world, as well as its potential environmental effects. Some basic principles are presented, and assessment and advice are provided for each category. Some suggestions for further field-based research on artificial downwelling, especially for long-term field research, are also given.

Artificial downwelling, which is an ecological engineering method, potentially alleviates bottom hypoxia by bringing oxygen-rich surface water down below the pycnocline. However, the downward flow is likely to disturb sediments (or induce sediment resuspension) when reaching the bottom and then have unwanted side effects on the local ecosystem. To evaluate this, our paper presents a theoretical model and experimental data for the sediment resuspension caused by artificial downwelling. The theoretical model considers the critical conditions for sediment resuspension and the scour volume with the downwelling flow disturbing sediment. Experiments with altered downwelling flow speeds, discharge positions relative to the bottom, and particle sizes of sediment were conducted in a water tank, and the results were consistent with our theoretical model. The results show that the critical Froude number (hereinafter Fr) for sediment resuspension is 0.5. The prevention of sediment resuspension requires the downwelling flow speed and the discharge position to be adjusted so that Fr &lt, 0.5, otherwise a portion of sediment is released into the water and its volume can be predicted by the derived formulation based on the Shields theory. Furthermore, sediment resuspension has side effects, such as a water turbidity increase and phosphorus release, the magnitudes of which are discussed with respect to engineering parameters. Further study will focus on field experiments of artificial downwelling and its environmental impacts.

Artificial upwelling by using airlift pump is considered a sustainable way in actualizing ocean fertilization, which could potentially alleviate the pressures on the fish stocks and human-driven climate change. However, few experimental data about the effects of operating parameters and injection method on the performance of the airlift artificial upwelling were found in the literature. In this paper, an airlift pump for artificial upwelling was investigated through three field experiments, in which airlift pumps of pipe length ranges from 20 to 28.3 m and pipe diameter ranges from 0.4 to 2 m, were designed and tested. Pumped water flow rate and injected air flow rate were measured to study the effects of different factors on the performance of airlift pump. The experiment results show that airlift pump efficiency is closely related to pipe diameter, submerged depth, submergence ratio and nozzle designs. There is no best nozzle for all the range of air flow rate, and the recommended nozzles are double-ring-shaped or star-shaped nozzles when the air flow rate is less or more than 220 L/min, respectively. Moreover, the lift effectiveness increases when the hole size of nozzle is enlarged, which indicates a relatively large bubble size will enhance the lift effectiveness.

Coastal hypoxia is on the rise around the world, reducing secondary production and ecosystem services in estuarine and coastal regions. We propose a tidal pump consisting of a 90° bend and a vertical downwelling pipe that potentially mitigates hypoxia in bottom waters. Downwelling kinetic head presents an approximate linear dependence on incident kinetic head. Experiments were carried out on a physical model at 1:80 scale covering a wide range of current speeds and density difference heads. Experimental findings confirm the theoretical model. Downwelling flow rate mainly depends on tidal current speed, relative density difference, the immersed length of the pump below the pycnocline and the pump geometry, the latter two of which allow engineers actively regulate downwelling flow. In the Changjiang estuary where hypoxia frequently occurs below the pycnocline during late summers, surface oxygen-rich water could be pumped into a depth 15.36 m below the pycnocline at a flow rate of 0.4 m3/s for 1.2 m pipe diameter. Further study will focus on the deployment of the tidal pump to obtain the optimal dissolved oxygen (DO) concentration field in bottom waters.

Ecological engineering by artificial upwelling for enhancing seaweed growth and consequently increasing nutrient removal from seawater has proved promising in combating intense coastal eutrophication. However, a key issue needs to be answered: how much economic and ecological benefit could this engineering bring if it were to be implemented in national aquaculture areas. This study estimated the promoting effect of nutrient concentration change induced by artificial upwelling on kelp growth using a model simulation based on the temperature, light intensity, and nutrient concentration data from three bays in Shandong Province, China&mdash, &nbsp, Aoshan Bay, Jiaozhou Bay, and Sanggou Bay. Our results indicate that ecological engineering by artificial upwelling can increase the average yield of kelp by 55 g per plant. Furthermore, based on the current existing kelp aquaculture area of China and the aquaculture density of 12 plants/m2, we inferred that this ecological engineering could increase the natural kelp yield by 291,956 t and the removal of nitrogen (N) and phosphorus (P) nutrients by 4875&ndash, 6422 t and 730&ndash, 1080 t, respectively.

China is now accelerating the development of an ecological engineering for carbon sequestration in coastal mariculture environments to cope with climate change. Artificial upwelling as the ecological engineering can mix surface water with bottom water and bring rich nutrients to the euphotic zone, enhance seaweed growth in the oligotrophic sea area, and then increase coastal carbon sequestration. However, one of the major obstacles of the artificial upwelling is the high energy consumption. This study focused on the development of energy management technology for air-lift artificial upwelling by optimizing air injection rate. The fundamental principle underlying this technology is that the mode and intensity of air injection are adjusted from the feedback of information on velocity variation in tidal currents, illumination, and temperature of the surface layer. A series of equations to control air injection was derived based on seaweed growth and solar power generation. Although this finding was originally developed for the air-lift artificial upwelling, it also can be used in other areas of engineering, such as water delivery, aeration, and oxygenation. The simulations show that using a variable air injection rate can lift more nitrogen nutrients of 28.2 mol than using a fixed air injection rate of 26.6 mol, mostly with the same energy cost. Using this control algorithm, the changed temperature and dissolved oxygen profiles prove the effective upwelling in the experiments and the average weights of kelp are 33.1 g in the experimental group and 10.1 g in the control group. The ecological engineering was successfully increasing crop yield for carbon sequestration in coastal mariculture environments.

The potential of artificial upwelling (AU) in enhancing transport of nutrient-rich bottom water to the surface, stimulating seaweed growth and consequently increasing organic carbon removal from coastal waters to land after harvest has attracted increasing scientific interest. This practice, however, hardly have field experiments to confirm the hypothesis. The coastal mariculture environment requires rigid AU system that not only can withstand rough weather conditions but also be effective in fertilizing the surface ocean. In this paper, a new solar-powered, air-lifted AU system was applied to study the potential effect on regional carbon removal. Experiments were conducted in the oligotrophic Aoshan Bay, Shandong Province, China. Comparison of the temperature and nutrient column between AU influenced site and the reference site suggests that the nutrient-rich bottom water has been successfully lifted to the surface. The results show that the growth of seaweeds was effectively stimulated by AU. The average weight of a single plant has increased by 8.98g, and consequently an extra carbon removal potential of 14.8 thousand tons in Chinese coastal waters could be expected if the system can be applied along the Chinese coastal waters.

As an ecological engineering project, artificial upwelling can enhance seaweed growth in the oligotrophic sea area by lifting bottom water, which is rich in nutrients, to the surface and thereby increase coastal carbon sequestration. Generally, engineering projects producing artificial upwelling occur far away from land and are self-powered using offshore solar energy or wind energy. The key to successfully implementing such engineering projects is to produce artificial upwelling with limited energy. With this in mind, an intelligent control system is designed for the energy management of the artificial upwelling engineering project that operates at AoShan Bay in Qingdao, China. This engineering project uses artificial upwelling to assist in the cultivation of macroalgae. The intelligent control system can automatically produce upwelling according to the battery condition and guarantee safety during operation. Meanwhile, users can monitor the system in real time with a Cloud platform. The functioning of the system and the effect of upwelling are confirmed by a sea trial. This research provides guidelines and technical support for the future design of intelligent control systems mounted on artificial upwelling engineering projects.

Ecological engineering by artificial upwelling is considered a promising way to improve water quality. Artificial upwelling could lift nutrient-rich bottom water to the surface, enhance seaweed growth and consequently increase nutrient removal from seawater. However, one of the major obstacles of the engineering application is to determine the suitable position of ecological engineering, which is critical for artificial upwelling&rsquo, s performance. In this paper, potential artificial upwelling positions in a semi-closed bay are simulated by using the unstructured-grid Finite-Volume Coastal Ocean Model (FVCOM). The results show that the upwelling position with relative small tidal current and close to corner will be helpful to increasing nutrient concentration of surface water, and be appropriate to build the ecological engineering. With proper design of the ecological engineering, it is possible to have a noticeable impact in semi-closed bay. Thus, artificial upwelling has the potential to succeed as a promising way to alleviate the eutrophication.

In order to investigate the long-term effects of artificial upwelling on the marine environment, Xiamen University, Zhejiang University, China Ocean University and other units have constructed an artificial upwelling demonstration area in Aoshan Bay, Qingdao City, China in September 2017. The main purpose of this paper is to develop a data acquisition and remote monitoring system that is enough robust to realize the large-scale, long-term, real-time and longrange monitoring needs of the demonstration area. The monitoring system, which is based on CAN-bus technology, wireless transmission technology and Amazon Web Service, has been initially completed and tested. The system can realize remote real-time acquisition of sensor data and video signal, which provide a solid foundation for long-term monitoring of upwelling environmental effects in the demonstration area.

The oceanic downwelling in nature can bring high concentrations of dissolved oxygen from the surface water into the bottom water. It can reduce the concentration of toxic substances such as ammonia, hydrogen sulfide, and heavy metals in the bottom water. It is an ecological restoration mechanism for the ocean. In 2007, Swedish scientists first proposed the concept of artificial method to produce downwelling, and through two years of experiments demonstrated the feasibility of using it for ecological rehabilitation in anoxic zones. However, this concept cannot be achieved through engineering. In this paper, Based on CFD simulation and experimental validation, downwelling velocity of the device is studied for different density and venturi contraction angles. The results show that: (1) With a density difference of 4 ${\mathrm {kg/m}}^{3}$ and a surface current velocity of 1-2 ${\mathrm {m/s}}$, the device can obtain a downwelling velocity of $0.01-1.18~{\mathrm {m/s}}$. (2) Under the same current conditions, the device can obtain the maximum downwelling velocity when the contraction angle is about 10°.

This paper studies bubble-entrained plume (BEP) behaviors in a crossflow and proposes a theoretical approach for predicting BEP trajectories and the separation points from the bubble swarm....

Hypoxia has been increasingly observed in estuaries and coastal marine ecosystems around the world. In this paper, a tide-powered artificial downwelling device is proposed to potentially alleviate hypoxia in bottom waters. The downwelling device mainly consists of a vertical square tube, a 90&deg, bend sitting on the top of the tube, two symmetrical-guide plates which installed alongside the vertical tube, a static mixer, and an artificial reef. Scale model experiments are performed with respect to different density difference heads, horizontal current velocities, and tube geometries. The results show that the downwelling flow rate is dependent on horizontal current velocity, tube geometry parameters, and the density profile of ambient water. In addition, increasing the equivalent diameter and bend radius of the device can decrease the total loss coefficient in the tube, which in turns enhance the downwelling efficiency. The two symmetrical-guide plates also generate obvious downwelling of surface water which further improves the whole performance of the device. Further work will need to determine the influence of the other parts of the device, such as the static mixer and artificial reef, on the downwelling efficiency.