Chlorophyll and plankton of the Gulf coastal waters of Saudi Arabia bordering a desalination plant

As on land, plants are the real producers in the sea, and on them depend all marine living resources and the basic sustainability of ecosystems. Primary production is performed by chlorophyll-bearing plants ranging from the tiny phytoplankton to the giant kelps through the process ofphotosynthesis. Zooplankton play an important role as secondary producers, and together with phytoplankton they support the vast assemblages of marine food chain with all their diversity and complexity. Data on chlorophyll pigments, phytoplankton and zooplankton are regarded as a sound basis for environmental appraisal of ecosystems. This paper presents a set of data collected from the Saudi Arabian coastal waters near the desalination plants in AI-Jubail. Materials were collected from six different sites covering the intake and discharge zones during cruises carried out in 1997-1998. Analyses of chlorophyll pigments were made using the spectrophotometric method. Plankton samples were collected using a Nansen plankton net with a mesh size of 75 μ and analyzed following standard procedures. Chlorophyll a, b, c and phaeophytin are the most commonly occurring pigments in seawater. Their concentrations showed wide fluctuation. The phytoplankton community was composed of 35 genera representing the Diatoms, Dinoflagellates and blue- green algae. Zooplankton were composed ofProtozoa, Coelenterata, Ctenophora, Aschelminthes, Annelida, Mollusca, Arthropoda, Echinodermata and Chordata. Arthropoda, represented by Cladocera, Copepoda and Crustacean larvae, formed the largest group followed by Chordata. The distribution of phyto- and zooplankton was examined and discussed on a seasonal, annual and inter-annual basis. In terms of species, overall species composition was not affected by plant discharge. The study brings out a greater understanding of the changes experienced by biotic communities as a result of impingement, entrainment and entrapment consequent to water passage through the plant structures. The study reflects the ecological relationships that the phytoplankton and the zooplankton of the region possess with respect to intake and discharge. Further, the study has brought to light a very redeeming feature of the ecosystem to sustain its productivity and planktonic abundance. It was observed that seawater temperature, conductivity and total suspended solids did not act as limiting factors. Besides throwing much light on the little known biological aspects of desalination sites, the data provided constitute a significant addition to the knowledge base of marine living resources in an industrial zone of Gulf coastal waters.     

Marine Wastewater Discharges from Multiport Diffusers. II: Unstratified Flowing Water

Laboratory experiments on the near-field mixing of buoyant plumes discharged from multiport diffusers into unstratified flowing water are reported. The spatial variation of dilution was measured by a newly developed three-dimensional laser-induced fluorescence system and a microconductivity probe. The near-field hydrodynamics are complex. The plumes discharged upstream dilute and merge more rapidly than those discharged downstream. Even with wide port spacing, the plumes eventually merge to form a laterally uniform surface wastefield. The density profile in this wastefield becomes gravitationally stable and suppresses mixing, marking the end of the near field. The value of the port spacing ratio, s/H, below which the discharge approximates a line plume is greater for discharge into a flowing current than into a stationary environment, so the port spacing plays a lesser role in a flowing current. The mixing and dilution that occurs in the surface layer is less than for a discharge into a stationary environment, and it decreases as the current speed increases. Semiempirical equations to predict the major near field characteristics are presented.     

暴雨后对下凹式立交及泵站设计的反思

2012年北京"7.21"特大暴雨后,对重灾区房山区的公路下凹式立交积水情况进行了调查统计,在此基础上,分析了下凹立交积水原因及共同的特点,总结了下凹式立交及泵站设计中呈现出的问题,并提出了在今后下凹式立交及泵站设计中相应的改进措施。     

Deposition from Particle-Laden, Plane, Turbulent, Buoyant Jets

Laboratory and computational fluid dynamics (CFD) model studies with turbulent, plane, particle-laden buoyant jets discharged horizontally into a quiescent ambient fluid have demonstrated that the presence of particles has no significant influence upon the buoyant jet trajectories over a wide range of forcing conditions and source concentrations of 0.1% or less. Bed deposition distributions show a large initial maximum close to the source, indicative of a dominant, localized particle fall-out from the buoyant jet margins. Beyond this near-source region, the distributions show a gradual decrease in particle deposition with increasing distance from the source, as a result of particle fall-out from the spreading surface layer generated by the buoyant jet impinging on the free surface of the receiving waters. In both cases, the deposition distributions scale well with the nondimensional settling parameter ws/b01/3 and the source Froude number F0. CFD simulations show good agreement with the laboratory data, particularly for deposition distributions downstream of the source. Additionally, the simulations indicate clearly that the receiving water boundaries can produce significant secondary return flows through fluid displacement by the spreading surface gravity current and its subsequent reflection.     

Experiments on Marine Wastewater Diffusers with Multiport Rosettes

The dispersion capabilities of two types of marine wastewater diffusers, one with risers containing eight radial ports (rosette) and the other with the ports uniformly distributed, were directly compared in laboratory experiments for three scenarios: stationary and flowing unstratified, and flowing stratified. Tracer concentration fields were measured with a three-dimensional laser-induced fluorescence system. The dispersion capabilities, particularly dilution, of the two diffuser types were similar. The primary differences occurred with no current where the rosette diffuser plumes were bent inwards, causing a dynamic interaction. This resulted in a small reduction in near field dilution, an increase in the spreading layer thickness, and a decrease of the near field length. These differences were virtually eliminated by a flowing current when the eight individual plumes from a rosette first merged with themselves and then with those from neighboring risers to become laterally quite uniform at the end of the near field. The major near field characteristics were primarily determined by the buoyancy flux per unit length. Temporal concentration fluctuations were high close to the diffuser and then decreased and leveled off near the end of the near field where the discharge-induced turbulence collapses. The fluctuations do not go to zero, however, owing to remnants of previous fluctuations.     

Marine Wastewater Discharges from Multiport Diffusers. III: Stratified Stationary Water

Experiments on the near-field mixing of wastewater discharged from multiport diffusers into a stationary density-stratified environment are reported for conditions typical of ocean sewage outfalls. Dilutions were measured with a microconductivity probe in which the test tank was stratified with a nonconducting solution; geometrical characteristics such as rise height and layer thickness were measured by planar laser-induced fluorescence in which the test tank was stratified with refractive-index matched fluids. The port spacing was varied over a wide range encompassing rapidly merging to nonmerging plumes. The end of the near-field occurs at a distance of order one plume rise height from the diffuser. At this point the turbulence and mixing induced by the discharge is effectively damped by the ambient stratification, and little near-field mixing occurs beyond it. The results were analyzed in terms of line and point-source parameters to deduce the ranges of port spacings for which line and point plume solutions apply. Equations to predict the near-field characteristics are presented.     

Overview of seawater concentrate disposal alternatives

This article discusses the available alternatives for ocean concentrate disposal, site specific factors involved in the selection of the most viable alternative for a given project, and the environmental permitting requirements and studies associated with their implementation. The article focuses on the three most widely used alternatives for ocean discharge of concentrate: direct discharge through new outfall; discharge through existing wastewater treatment plant outfall; and co-disposal with the cooling water of existing coastal power plant. Key advantages, disadvantages, environmental impact issues and possible solutions are presented for each discharge alternative. Results from recent salinity tolerance and toxicity study completed at the Carlsbad, California seawater desalination demonstration plant for a variety of sensitive marine organisms are presented. The practical implementation of this study along with other methods for analysis of the environmental impact of ocean discharges from large seawater reverse osmosis plants is illustrated with case study examples.     

Field Observations of Ipanema Beach Outfall

Field observations of the Ipanema Beach, Rio de Janeiro, Brazil, ocean sewage outfall were obtained by adding dye tracers to the effluent and simultaneously measuring oceanographic conditions. Four experiments were performed, two during unstratified conditions, and two during stratified conditions. When stratified, the plume was trapped below the thermocline with low dilution, around 35 to 1, when unstratified, the plume surfaced and the dilution increased to more than 100 to 1. The results were compared with predictions of some commonly used near field plume mathematical models: UM3, RSB, and CORMIX. With suitable assumptions, all the models reasonably predict near field dilution. RSB predicts near field results directly; for UM3 and CORMIX, it was assumed that the end of the near field occurs when the plume reaches its terminal rise height or impacts the free surface. Different assumptions about the shape of the density profiles in CORMIX resulted in widely differing predictions of dilution. While the gross properties of the plume can be reasonably predicted by plume models, there remain many aspects which cannot be, particularly the patchy nature of the wastefield that has been observed here and in other field tests.     

Submarine tailings placement by a copper mine in the deep anoxic zone of the Black Sea

Copper mine tailings are discharged to the anoxic zone of the Black Sea at 350 m depth, and there is currently consideration of reducing this discharge depth. Oceanographic sampling has provided data allowing calculating whether dilute buoyant plumes will separate from the tailings density current as predicted. Calculations for various discharge rates and slurry dilutions indicate that such plumes will rise 89 m above the discharge depth, hence will remain in the deep anoxic zone below the permanent pycnocline at 150 m depth at both the present and currently proposed sites. There is some indication from relative seawater density measures that these plumes will drift rather than spreading diffusely. Plume separation from controlled discharges of the tailings slurry was confirmed by visual observations in an experimental tank. The oceanographic sampling also showed that trace element levels in the seawater by the discharge point remained below Turkish marine receiving water quality criteria.     

Sedimentation from Buoyant Jets

An integral model is developed to describe sedimentation from a turbulent, buoyant jet injected at an angle into a stationary, uniform ambient fluid. Entrainment is modeled using the standard entrainment assumption and sediment is assumed to fall from the jet where the outward component of the fall velocity normal to the jet boundary exceeds the inward entrainment velocity. When appropriately scaled by source momentum and buoyancy fluxes, turbulent, buoyant jets may be described in terms of a single parameter: the angle θ0 between the flow and the horizontal at the virtual origin (which is close to the actual source for large initial densimetric Froude numbers). Including sedimentation in the model introduces a further parameter ws, which is the ratio of the fall speed of the sedimenting particles to a typical entrainment velocity (and so wS is a nondimensional fall speed). An important result is that this ratio is independent of the source speed, so that the proportion of the sediment load deposited near the source is independent of the flow rate. Sediment remaining in the plume beyond the near-source region is deposited when the plume spreads horizontally once it reaches the free surface. Results for plume shapes, deposition patterns, and the proportion of sediment load deposited in the near-source region (as functions of θ and ws) are given. The results are supported by some preliminary laboratory experiments. The effects of flow in the ambient fluid are discussed briefly and a further parameter uF is introduced, which is the ratio of the ambient flow speed to a typical entrainment velocity (again this ratio is independent of the flow rate).