Three-fluid retention in porous media involving water, PCE and air

A classical way to obtain three-fluid retention curves in porous media from measured two-fluid retention curves is based on the Leverett concept, which states that the total volumetric liquid content in a water-wet porous medium, containing water, a nonaqueous-phase liquid (NAPL) and air, is a function of the capillary pressure across the interface between the continuous NAPL and air. This functional relationship results from the assumed condition that in a three-fluid porous medium, the intermediate wetting fluid spreads over the water-air interface. Application of Leverett's concept may not be valid, however, for nonspreading NAPLs like perchloroethylene (PCE). This paper discusses measurements of both PCE-air and water-PCE-air retention curves using a long vertical column in conjunction with a dual-energy gamma radiation system. The data indicate that the Leverett concept was applicable only until a critical PCE saturation had been reached.     

Predicting change in fish mercury concentrations following reservoir impoundment

Fish mercury concentrations frequently increase after impoundment of a reservoir. Soil flooding releases organic matter and nutrients, providing food to bacterial communities that methylate inorganic mercury. Methylation and bioaccumulation are the primary pathways for mercury accumulation in fish. We investigated if changes in fish mercury concentrations could be predicted from the change in reservoir size. Data for three fish species, northern pike (Esox lucius), walleye (Stizostedion vitreum), and lake whitefish (Coregonus clupeaformis) from reservoirs in northern Manitoba and northern Quebec were used to evaluate four simple models of change in mercury with change in flooded area. For three additional fish species, all primary carnivores, the preferred model consisted of a single exponential enrichment term. This model successfully predicted two cases not used in model development-one with a large change in area and one with a small change in area. Models with good predictive skill can be developed when the underlying dynamics are known.     

Miscible fluid displacement stability in unconfined porous media:: Two-dimensional flow experiments and simulations

In situ flushing groundwater remediation technologies, such as cosolvent flushing, rely on the stability of the interface between the resident and displacing fluids for efficient removal of contaminants. Contrasts in density and viscosity between the resident and displacing fluids can adversely affect the stability of the displacement front. Petroleum engineers have developed techniques to describe these types of processes; however, their findings do not necessarily translate directly to aquifer remediation. The purpose of this laboratory study was to investigate how density and viscosity contrasts affected cosolvent displacements in unconfined porous media characterized by the presence of a capillary fringe. Two-dimensional flow laboratory experiments, which were partially scaled to a cosolvent flushing field experiment, were conducted to determine potential implications of flow instabilities in homogeneous sand packs. Numerical simulations were also conducted to investigate the differential impact of fluid property contrasts in unconfined and confined systems. The results from these experiments and simulations indicated that the presence of a capillary fringe was an important factor in the displacement efficiency. Buoyant forces can act to carry a lighter-than-water cosolvent preferentially into the capillary fringe during displacement of the resident groundwater. During subsequent water flooding, buoyancy forces can act to effectively trap the cosolvent in the capillary fringe, contributing to the inefficient removal of cosolvent from the aquifer.     

Three-dimensional patterns of moisture, water repellency, bromide and pH in a sandy soil

Soil water repellency might lead to preferential flow of water and solutes through the unsaturated zone of soils. To study this process in a water repellent sandy field soil, a bromide tracer had been applied on a 2.2 m long and 0.4 m wide plot. The bromide application rate was 8 g/m², and the plot was sampled using 100 cm³ steel cylinders after 52 mm of rainfall in 12 days. A total of seven layers were sampled to a depth of 74 cm. Each layer was sampled at 240 locations in a 40 by 6 grid. All samples were used for the determination of soil water content, degree of actual and potential water repellency, bromide concentration and pH. The spatial distribution of these properties was visualized three-dimensionally and compared. The degree of water repellency, bromide concentration, and pH distribution bore close resemblance to the fingered flow induced soil water content distribution. The degree of potential water repellency was relatively low in places with such fingers. Actual water repellency occurred between the fingers at the dry spots. Bromide was not found, or only in very low concentrations, in such places. Bromide depth profiles clearly indicated the occurrence of diverging flow in the wetter subsoil. Most likely, manuring activities during the last decades resulted in relatively high pH values in the topsoil, and in the subsoil along the recurring fingered flow pathways.     

Marginal bleaching of thalli of Rhizocarpon as evidence for acid rain in the Norra Storfjället, Sweden

Recent lichen surveys in the foreland of The Syterb?cken glacier reveal that the crustose lichens, principally species of Rhizocarpon section Rhizocarpon, exhibit marginal bleaching, readily distinguishable from normal pigmented forms. The largest elliptical thallus of Rhizocarpon measured 290 mm maximum diameter on a bedrock outcrop beyond the margin of Little Ice Age moraines in the upper Syterb?cken Valley. Many small and large thalli of Rhizocarpon suffered damage to the periphery of individual thalli. We examine here some of the possible hypotheses explaining these occurrences. Among others, these are bedrock lithology, ice crystal blasting, long-term snowbank cover, ultraviolet exposure and acid rain. While at this time none of the possibilities can be ruled out entirely, acid rain would appear to be at least one of the factors involved. Acid rain, which is known to produce a soil pH as low as 3.3 in the field area, appears to provide a high input of H(+) ions that the lichen algal component cannot withstand. However, the lack of similar effects on associated foliose or fruticose forms raises the possibility that perhaps two or more factors specific to the environment of Rhizocarpon are operating.     

The interactive effects of low pH, toxic metals, and DOC on a simulated temporary pond community

The effects of pH, potentially toxic metals, and dissolved organic carbon (DOC) on a freshwater, palustrine wetland assemblage (three amphibian species, one mosquito genus, and 18 genera of algae) were examined in 500 liter outdoor mesocosms. The design was fully factorial and exposure levels were set to represent concentrations that occur naturally in temporary ponds in central Pennsylvania, an acid-impacted region of the USA. Water chemistry was precisely regulated by use of an artificial pond water rather than using stream water or well water with partially unknown composition. Jefferson (Ambystoma jeffersonianum) and spotted salamanders (A. maculatum) were negatively impacted by low pH and high metal concentrations. Wood frogs (Rana sylvatica) were negatively impacted by high DOC and low pH. These negative effects included increased time to metamorphosis and decreased survival and wet body mass at metamorphosis. Mosquito emergence was unaffected by pH, metals, or DOC. All three abiotic factors (metals, pH, and DOC) interacted to determine algal taxonomic composition. Hence, abiotic conditions may determine amphibian reproductive success both directly and indirectly, via effects on algae, since a primary food source of salamanders, zooplankton, are affected by changes in algal composition. These complex interactions should be considered in evaluating the possible toxicity of pond waters to fauna and flora. Until now, pH alone has been considered the primary limiting factor for amphibians breeding in temporary ponds.     

Fractionation of fulvic acids: characteristics and complexation with copper

Two fulvic acid samples isolated from Suwannee river (International Humic Substance Society) and Feeitsuey reservoir were subjected to gel filtration chromatography (GFC) for molecular size fractionation. The GFC-eluted samples were separated into three groups corresponding to the molecular weight ranges: < 220, 220-1000, and 1000-4000. Fluorescence quenching techniques were employed for determining the conditional stability coefficient and kinetic parameters of copper complexation with the three fractions of fulvic acids. Experimental conditions were pH 6, 5 x 10(-5)m total copper and 5 mg C litre(-1) of fulvic acids. The conditional stability coefficients of the fulvic acid fractions were in the order of 0.9-3.3 x 10(5)m(-1), and the forward and reverse rate constants were in the order of 6.9-12.4 x 10(3)m(-1) s(-1) and 3.5-8.0 x 10(-2) s(-1). Information could be useful in modelling copper transport in the hydrosphere.     

多配位基螯合离子交换纤维的研究及其进展

离子交换纤锥作为具有高吸附佐的吸附材料，在金属离子的分离、富集、回收等方面，以及在水净处理净化处理领域得到了迅速的发展及应用，引起了人们的极大兴趣。本文对近十几年来离子交换纤维的合成方法路线、性能研究以及在痕量元素的分离、富集和水处理方面的应用进行了综述，并对目前离子交换纤维的研究中存在的问题提出了一些看法。