Energy dissipation, flow resistance and gas-liquid interfacial area in skimming flows on moderate-slope stepped spillways

With the re-evaluation and revision of a number of design floods, several embankment overtopping protection systems have been developed and a common technique is the construction of a stepped spillway on the downstream slope. For such moderate slope stepped channels, detailed air–water flow measurements were performed in a large facility with a focus on the rate of energy dissipation, flow resistance, air–water interfacial areas and re-aeration rates. Past and present experimental results showed a significant aeration of the flow. The median dimensionless residual head was about 3 × d_c for the 21.8° sloping chute and smaller than that for flatter slopes (θ = 3.4° and 15.9°). The flow resistance results yielded an equivalent Darcy friction factor of about 0.25 implying a larger flow resistance for the 21.8° slope angle than for smaller slope angles. The re-aeration rate was deduced from the integration of the mass transfer equation using measured air–water interfacial areas and air–water flow velocities. The results suggested an increasing re-aeration rate with increasing rate of energy dissipation. The stepped invert contributed to intense turbulence production, free-surface aeration and large interfacial areas. The experimental data showed however some distinctive seesaw pattern in the longitudinal distribution of air–water flow properties with a wave length of about two step cavities. While these may be caused by the interactions between successive adjacent step cavities and their interference with the free-surface, the existence of such “instabilities” implies that the traditional concept of normal flow might not exist in skimming flows above moderate-slope stepped spillways.     

Flow,flapping, and photosynthesis ofNereocystis leutkeana: a functional comparison of undulate and flat blade morphologies

A number of species of macroalagae possess a flat, strap-like blade morphology in habitats exposed to rapidly-moving water whereas those at protected sites have a wider, undulate blade shape. We have explored the functional consequences of flat, narrow vs. wide, undulate blade morphologies in the giant bull kelpNereocystis luetkeana. Our study focused on the behavior of blades in ambient water currents and the consequences of that behavior to breakage and to photosynthesis. In flowing water, the narrow, flat blades flap with lower amplitude and collapse together into a more streamlined bundle than do wide, undulate blades, and hence experience lower drag per blade area at a given flow velocity. If the algae at current-swept sites had ruffled blades, drag forces would sometimes be sufficient to break the stipes. However, flat blades in a streamlined bundle experience more self-shading than do undulate blades, which remain spread out in water currents. Thus, there is a morphological trade-off between reducing drag and reducing self-shading. Photosynthetic¹⁴C-HCO₃ uptake rates decrease in slow flow when the boundary layer along the blade surface across which diffusion takes place is relatively thick. However, blade flapping, which stirs water near the blade surface, enhances carbon uptake rates in slow water currents for both the undulate and the flat morphologies.     

Budgets of turbulent kinetic energy,Reynolds stresses,and dissipation in a turbulent round jet discharged into a stagnant ambient

Environmental Fluid Mechanics - This paper presents a set of stereoscopic particle image velocimetry (SPIV) measurements of a turbulent round water jet (jet exit Reynolds number $$Re = 2679$$ and...     

Residues,half-life times,dissipation, and safety evaluation of the acaricide fenpyroximate applied on grapes

A validated high-performance liquid chromatography–diode array detector method for simultaneous determination of the acaricide fenpyroximate on grape was developed. Estimated limit of detection and limit of quantification for fenpyroximate were 0.01 and 0.05 mg kg^?1, respectively. The intra- and inter-day precisions performed with relative standard deviation were better than 9.3% and 8%, respectively, while recoveries were in the range of 88.5%–100.4%. Residue levels of fenpyroximate in grape samples collected 10 days after field application were below the established maximum residue level values. The dissipation rates of fenpyroximate were described using first-order kinetics and its half-life, were approximately 3.5 days in grape. This study provides basic information for developing regulations to safeguard the use of fenpyroximate in grapes and prevent any potential health concerns for consumers.     

Development of similarity relationships for energy dissipation rate and temperature structure parameter in stably stratified flows: a direct numerical simulation approach

In this study, a newly developed direct numerical simulation (DNS) solver is utilized for the simulations of numerous stably stratified open-channel flows with bulk Reynolds number (Re _b ) spanning 3400–16,900. Overall, the simulated bulk Richardson number (\(Ri_b\)) ranges from 0.08 (weakly stable) to 0.49 (very stable). Thus, both continuously turbulent and (globally) intermittently turbulent cases are represented in the DNS database. Using this comprehensive database, various flux-based and gradient-based similarity relationships for energy dissipation rate (ε) and temperature structure parameter (\(C_T^2\)) are developed. Interestingly, these relationships exhibit only minor dependency on Re _b . In order to further probe into this Re _b -effect, similarity relationships are also estimated from a large-eddy simulation (LES) run of an idealized atmospheric boundary layer (very high Re _b ) case study. Despite the fundamental differences in the estimation of ε and \(C_T^2\) from the DNS- and the LES-generated data, the resulting similarity relationships, especially the gradient-based ones, from these numerical approaches are found to be remarkably similar. More importantly, these simulated relationships are also comparable, at least qualitatively, to the traditional observational data-based ones. Since these simulated similarity relationships do not require Taylor’s hypothesis and do not suffer from mesoscale disturbances and/or measurement noise, they have the potential to complement the existing similarity relationships.     

Nanomaterials for water cleaning and desalination,energy production,disinfection, agriculture and green chemistry

Nanomaterials may help to solve issues such as water availability, clean energy generation, control of drug-resistant microorganisms and food safety. Here we review innovative approaches to solve these issues using nanotechnology. The major topics discussed are wastewater treatment using carbon-based, metal-based and polymeric nanoadsorbents for removing organic and metal contaminants; nanophotocatalysis for microbial control; desalination of seawater using nanomembranes; energy conversion and storage using solar cells and hydrogen-sorbents nanostructures; antimicrobial properties of nanomaterials; smart delivery systems; biocompatible nanomaterials such as nanolignocellulosis and starches-based materials, and methods to decrease the toxicity of nanomaterials. Significantly, here it is reviewed two ways to palliate nanomaterials toxicity: (a) controlling physicochemical factors affecting this toxicity in order to dispose of more safe nanomaterials, and (b) harnessing greener synthesis of them to bring down the environmental impact of toxic reagents, wastes and byproducts. All these current challenges are reviewed at the present article in an effort to evaluate environmental implications of nanomaterials technology by means of a complete, reliable and critical vision.     

Calorimetric studies on the energy metabolism of an infaunal bivalve,Abra tenuis,under normoxia,hypoxia and anoxia

Direct calorimetry was employed to measure the energy metabolism of infaunal bivalves, Abra tenuis, collected from a tidal lagoon in the Fleet, southern England, in June 1989, at various oxygen partial pressures. A significant anaerobic component (i.e., 20% of total metabolic rate) was detected under normoxia, presumably brought about by the intermittent ventilatory activity of this bivalve under these conditions. Under hypoxia (2.3 to 10 kPa, or 11 to 48% of full air saturation), however, the energy metabolism was maintained fully aerobic; the measured heat equivalent of oxygen uptake was not significantly different from the theoretical ranges for fully aerobic catabolism. Under anoxia, the rate of heat dissipation was reduced to 5–6% of the normoxic rate of heat dissipation. This conserves energy expenditure and would thus increase resistance of A. tenuis to anoxia or emersion. Physiological compensation by A. tenuis under conditions of declining oxygen tension involved a marked increase in ventilation rate. Comparison between fed and starved individuals indicated that costly physiological processes, such as digestion, absorption and growth declined at 10 and 5 kPa and were arrested at P_{O 2} (oxygen partial pressure) levels below 2.3 kPa. The present study provides evidence that there are no major differences between the metabolic responses of epifaunal suspension-feeding (eg. Mytilus edulis) and infaunal deposit-feeding (eg. A. tenuis) bivalves when exposed to environmental hypoxic stress.     

Dynamic impacts of energy use,agricultural land expansion,and deforestation on CO2 emissions in Malaysia

Environmental and Ecological Statistics - This study empirically investigates the nexus among energy use, agricultural land expansion, deforestation, and carbon dioxide (CO2) emissions in Malaysia....     

Effects of starvation,and light and dark on the energy metabolism of symbiotic and aposymbiotic sea anemones,Anthopleura elegantissima

Rates of oxygen and carbon-dioxide exhange were measured in symbiotic and aposymbiotic specimens of the sea anemone Anthopleura elegantissima while fed and starved under light or dark conditions. Respiratory quotients indicated that fed anemones switched from a carbohydrate to a fat catabolism when starved, with the exception that symbiotic individuals starved in the light showed a pronounced carbohydrate catabolism for over 1 month. The source of the carbohydrate was probably photosynthate translocated by the dinoflagellate Symbiodinium (=Gymnodinium) microadriaticum (Freudenthal) living in the anemones' tissues. The starved symbiotic anemones maintained in the light had lipid levels not significantly different from fed controls and 44 to 61% higher than starved aposymbiotic anemones after 1 month. Thus, the quality and quantity of the metabolic flux from the symbionts to the sea anemone were sufficient to conserve the host's lipid reserves.     

Synthesis and application of titanium dioxide photocatalysis for energy,decontamination and viral disinfection: a review

Environmental Chemistry Letters - Global pollution is calling for advanced methods to remove contaminants from water and wastewater, such as TiO2-assisted photocatalysis.  The...     

红壤坡地降雨产流产沙动态过程模拟试验研究

研究以浙江省兰溪水土保持综合试验站为研究基地,通过设定特定植被覆盖度（15%）不同坡度（8°、15°、20°）的径流试验小区,小区面积为2m2,采用野外人工模拟降雨试验方法,对降雨强度（0.8～2.9mm·min-1）范围内,红壤坡地产流和产沙随雨强和坡度的变化特性进行了模拟试验。通过32场模拟降雨试验数据的分析,得出结论如下：①产沙量与雨强呈指数函数关系,产流量与雨强呈幂函数关系,径流量与产沙量的相关性大于雨强与径流、雨强与产沙;②随坡度的增大,产流时刻提前,泥沙起动和产沙突增的雨强临界减小;③随坡度增大,累积产沙量的递增速率比累积径流量的递增速率要快;④场降雨侵蚀模数与雨强的相关性随着坡度的增大而增强。     

A study on the Spatial Distribution of Nitrogen and Phosphorus Balance, and Regional Nitrogen Flow Through Crop Production

The spatial distribution patterns of the nitrogen and phosphorus input/intake amounts in crop production within two small basins are examined, based upon a cropping unit distribution map that is obtained from remote sensing data analysis. Firstly, we examine the availability and suitability of approaches to the spatial distribution analysis of cultivation patterns classified from material flow characteristics of crop production using seasonal remote-sensing data. Secondly, material flow units in crop production are grouped according to the cultivation patterns obtained from the remote-sensing data analysis. Consequently, the spatial patterns of the amounts of both nitrogen and phosphorus inputs/intakes through crop production on farmland are examined and their spatial distribution maps are prepared according to the material flow units. In addition, we developed a nitrogen flow and runoff model and the model is simulated based on the examination of the results of spatial distribution patterns of the material flow units. The annual nitrogen runoff from small catchments, where various crops are cultivated, varies from 2.7 kg ha^–1 year^–1 to 108 kg ha^–1 year^–1 and the annual balanced losses of nitrogen in small catchments varied from –30 kg ha^–1 year^–1 to 101 kg ha^–1 year^–1. Also, the monthly changes in soil nitrogen of each material flow unit is estimated at –55 kg ha^–1 as a maximum decrease and 114 kg ha^–1 as a maximum increase. These results indicate that the spatial distribution patterns of nutrient input and intake through agricultural activities should be considered when analyzing the material flows and nutritient movement in soil–water systems in rural areas for watershed environmental control and regional agricultural management.     

Trophic ecology of large predatory reef fishes: energy pathways, trophic level, and implications for fisheries in a changing climate

Large predatory fishes are disproportionately targeted by reef fisheries, but little is known about their trophic ecology, which inhibits understanding of community dynamics and the potential effects of climate change. In this study, stable isotope analyses were used to infer trophic ecology of a guild of large predatory fishes that are targeted by fisheries on the Great Barrier Reef, Australia. Each of four focal predators (Plectropomus leopardus, Plectropomus maculatus, Lethrinus miniatus and Lutjanus carponotatus) was found to have a distinct isotopic signature in terms of δ¹³C and δ¹⁵N. A two-source mixing model (benthic reef-based versus pelagic) indicated that P. leopardus and L. miniatus derive the majority (72 and 62 %, respectively) of their production from planktonic sources, while P. maculatus and L. carponotatus derive the majority (89 and 74 %, respectively) of their production from benthic reef-based sources. This indicates that planktonic production is important for sustaining key species in reef fisheries and highlights the need for a whole-ecosystem approach to fisheries management. Unexpectedly, there was little isotopic niche overlap between three of four focal predators, suggesting that inter-specific competition for prey may be low or absent. δ¹⁵Nitrogen indicated that the closely related P. leopardus and P. maculatus are apex predators (trophic level > 4), while δ¹³C indicated that each species has a different diet and degree of trophic specialisation. In view of these divergent trophic ecologies, each of the four focal predators (and the associated fisheries) are anticipated to be differentially affected by climate-induced disturbances. Thus, the results presented herein provide a useful starting point for precautionary management of exploited predator populations in a changing climate.     

Allocation of organic material and energy to the holdfast,stipe, and fronds inPostelsia palmaeformis (Phaeophyta: Laminariales) on the California coast

Postelsia palmaeformis were collected from the lower intertidal at Pigeon Point, California, USA, in May 1987, and the proximate composition and allocation of energy to the various body components were determined. The holdfast and stipe have a proximate composition (% dry weight) of ca. 40% ash, 5.3% protein, 1% lipid, 2% soluble carbohydrate, and 55% insoluble carbohydrate. The fronds have a proximate composition of ca. 25% ash, 6.5% protein, 2% lipid, 3% soluble carbohydrate, and 65% insoluble carbohydrate. The energetic level was ca. 12 kJ g^-1 dry wt and ca. 19 kJ g^-1 ash-free dry wt. The relative proportion of three plant components varied, comprising 26, 39, and 35% wet wt and 20, 42, and 38% kJ for the holdfast, stipe, and fronds, respectively. A plant with a basal stipe diameter of 33 mm contains 114 g wet wt and 266 kJ. The maximal density found in May 1987 was 826 plants, 49 301 g wet wt, and 106 157 kJ m^-2.P. palmaeformis differs in these characteristics from another intertidal pheophyte,Durvillaea antarctica, that is found in a high-energy intertidal zone.     

Flow cytometric assessment of the effects of chlorine,chloramine, and UV on bacteria by using nucleic acid stains and 5-cyano-2,3-ditolyltetrazolium chloride

Flow cytometry (FCM) has been widely used in multi-parametric assessment of cells in various research fields, especially in environmental sciences. This study detected the metabolic activity of Escherichia coli and Staphylococcus aureus by using an FCM method based on 5-cyano-2,3-ditolyltetrazolium chloride (CTC); the accuracy of this method was enhanced by adding SYTO 9 and 10%R2A broth. The disinfection effects of chlorine, chloramine, and UV were subsequently evaluated by FCM methods. Chlorine demonstrated stronger and faster destructive effects on cytomembrane than chloramine, and nucleic acids decomposed afterwards. The metabolic activity of the bacteria persisted after the cytomembranewas damaged as detected using CTC. Low-pressure (LP) UV or medium-pressure (MP) UV treatments exerted no significant effects on membrane permeability. The metabolic activity of the bacteria decreased with increasing UV dosage, and MP-UV was a stronger inhibitor of metabolic activity than LP-UV. Furthermore, the membrane of Gram-positive S. aureus was more resistant to chlorine/chloramine than that of Gram-negative E. coli. In addition, S. aureus showed higher resistance to UV irradiation than E. coli.

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