Turbulent air–water flows in hydraulic structures: dynamic similarity and scale effects

In hydraulic structures, free-surface aeration is commonly observed: i.e., the white waters. The air bubble entrainment may be localised (hydraulic jumps, plunging jets) or continuous along an interface (water jets, chutes). Despite recent advances, there are some basic concerns about the extrapolation of laboratory results to large size prototype structures. Herein the basic air bubble entrainment processes are reviewed and the relevant dynamic similarities are discussed. Traditionally, physical studies are conducted using a Froude similitude which implies drastically smaller laboratory Reynolds numbers than in the corresponding prototype flows. Basic dimensional analyses are developed for both singular and interfacial aeration processes. The results are discussed in the light of systematic investigations and they show that the notion of scale effects is closely linked with the selection of relevant characteristic air–water flow properties. Recent studies of local air–water flow properties highlight that turbulence levels, entrained bubble sizes and interfacial areas are improperly scaled based upon a Froude similitude even in large-size models operating with the so defined Reynolds numbers ρ _w × q _w/μ _w up to 5 E+5. In laboratory models, the dimensionless turbulence levels, air–water interfacial areas and mass transfer rates are drastically underestimated.     

A study on the effects of four heavy metals on five species of chironomous larvae present on Mahé Island of Seychelles

A study was conducted on the island of Mahé, Seychelles, on five species of chironomous larvae endemic to the island. The chironomous larvae were exposed to four heavy metals – copper (Cu), cadmium (Cd), mercury (Hg), and zinc (Zn), for a 96-hr period, and the LC₅₀ values were calculated. It was observed that the most sensitive species of chironomous larvae was Gymnometriocnemus mahensis. The least sensitive form of chironomous larvae examined was Paramerina minima. The 96-hr LC₅₀ values obtained for Tanypus complanatus for Cu, Cd, Hg, and Zn were 1.9 (1.73–2.09), 1.35 (1.17–1.57), 0.33 (0.26–0.43), and 28.96 (27.03–31.03) ppm, respectively. Similar results were obtained for other species studied.     

National water footprint in an input–output framework—A case study of China 2002

Water footprint is an indicator showing the consumption impact on environment with water equivalent, which allows a detailed quantification of water use directly and indirectly in sectors for the domestic and abroad final consumption. This paper presents a framework of calculating national water footprint (NWF) with input–output method on China 2002. The results indicated that the NWF of China was 381 m³/cap yr in 2002. A new indicator termed as national water footprint intensity (NWFI) is also derived from NWF to evaluate the water consumption intensities of different sectors. Then the evaluation of virtual water trade in sectors is followed, the results of which give a detailed quantification of net virtual water import of sectors, verifying that China is a net virtual water exporter concerning the whole national sectors, which is different from the previous studies. Finally, it is suggested that the sectors with high NWFI and volume of net virtual water export should be regarded as the priority of Chinese water-saving strategy.     

Effects of bedform migration on nutrient fluxes at the sediment–water interface: a theoretical analysis

Environmental Fluid Mechanics - Nutrient fluxes at the sediment–water interface are essential for water quality and aquatic ecosystems. In this study, a unified expression for the sediment...     

A coupled numerical model to investigate the air–sea interaction at the coastal upwelling area of Cabo Frio,Brazil

This work investigates the capability of an oceanic numerical model dynamic and thermodynamically coupled to a three-dimensional mesoscale atmospheric numerical model to simulate the basic features of the air–sea interaction in the coastal upwelling area of Cabo Frio (RJ, Brazil). The upwelling/downwelling regime is an important feature in the oceanic circulation of Cabo Frio and determines the sustainability of local ecosystems. This regime is predominantly driven by the atmospheric circulation and is well documented, being suitable to be used as test reference for atmospheric and oceanic coupled and uncoupled models. The oceanic boundary conditions, coastline shape and coupling effect have been tested. The uncoupled oceanic model forced by a NE (SW) wind field generates a realistic upwelling (downwelling) phenomenon regardless of the proximity of the lateral boundary and how realistic is the shape of the coastline. The atmospheric-oceanic coupled model generates an upwelling location and intensity similar to the uncoupled simulation, but the upwelling is gradually enhanced by the sea-breeze circulation. It also generates vertical profiles of mixing ratio that compare better to the observations than the uncoupled simulation and air potential temperature and wind vertical profiles that represent particular features of the atmospheric circulation at Cabo Frio.     

Impact of raking and bioturbation-mediated ecological manipulation on sediment–water phosphorus diagenesis: a mesocosm study supported with radioactive signature

The study examined the impact of raking and fish bioturbation on modulating phosphorus (P) concentrations in the water and sediment under different trophic conditions. An outdoor experiment was set to monitor physicochemical and microbiological parameters of water and sediment influencing P diagenesis. A pilot study with radioactive ³²P was also performed under the agency of raking and bacteria (Bacillus sp.). Raking was more effective in release of P under unfertilized conditions by significantly enhancing orthophosphate (35%) and soluble reactive phosphate (31.8%) over respective controls. Bioturbation increased total and available P in sediments significantly as compared to control. The rates of increase were higher in the unfertilized conditions (17.6–28.4% for total P and 12.2 to 23.2% for available P) than the fertilized ones (6.5–12.4% for total P and 9.1 to 15% for available P). The combined effects of raking and bioturbation on orthophosphate and soluble reactive phosphate were also stronger under unfertilized state (54.5 and 81.8%) than fertilized ones (50 and 70%). The tracer signature showed that coupled action of introduced bacteria and repeated raking resulted in 59.2, 23 and 16% higher counts of radioactive P than the treatments receiving raking once, repeated raking and bacteria inoculation, respectively. Raking alone or in sync with bioturbation exerted pronounced impact on P diagenesis through induction of coupled mineralization and nutrient release. It has significant implication for performing regular raking of fish-farm sediments and manipulation of bottom-grazing fish to regulate mineralization of organic matter and release of obnoxious gases from the system. Further, they synergistically can enhance the buffering capacity against organic overload and help to maintain aquatic ecosystem health.

     

Ambient air particulates and particulate-bound mercury Hg(p) concentrations: dry deposition study over a Traffic,Airport, Park (T.A.P.) areas during years of 2011–2012

The main purpose of this study was to monitor ambient air particles and particulate-bound mercury Hg(p) in total suspended particulate (TSP) concentrations and dry deposition at the Hung Kuang (Traffic), Taichung airport and Westing Park sampling sites during the daytime and nighttime, from 2011 to 2012. In addition, the calculated/measured dry deposition flux ratios of ambient air particles and particulate-bound mercury Hg(p) were also studied with Baklanov & Sorensen and the Williams models. For a particle size of 10 μm, the Baklanov & Sorensen model yielded better predictions of dry deposition of ambient air particulates and particulate-bound mercury Hg(p) at the Hung Kuang (Traffic), Taichung airport and Westing Park sampling site during the daytime and nighttime sampling periods. However, for particulates with sizes 20–23 μm, the results obtained in the study reveal that the Williams model provided better prediction results for ambient air particulates and particulate-bound mercury Hg(p) at all sampling sites in this study.