A surface structural model for ferrihydrite II: Adsorption of uranyl and carbonate

The adsorption of uranyl (UO₂²⁺) on ferrihydrite has been evaluated with the charge distribution (CD) model for systems covering a very large range of conditions, i.e. pH, ionic strength, CO₂ pressure, U(VI) concentration, and loading. Modeling suggests that uranyl forms bidentate inner sphere complexes at sites that do not react chemically with carbonate ions. Uranyl is bound by singly-coordinated surface groups present at particular edges of Fe-octahedra of ferrihydrite while another set of singly-coordinated surface groups may form double-corner bidentate complexes with carbonate ions. The uranyl surface speciation strongly changes in the presence of carbonate due to the specific adsorption of carbonate ions as well as the formation of ternary uranyl-carbonate surface complexes. Data analysis with the CD model suggests that a uranyl tris-carbonato surface complex, i.e. (UO₂)(CO₃)₃⁴⁻, is formed. This species is most abundant in systems with a high pH and carbonate concentration. This finding differs significantly from previous interpretations made in the literature. At high pH and low carbonate concentrations, as can be prepared in CO₂-closed systems, the model suggests the additional presence of a ternary uranyl-monocarbonato complex. The binding mode (type A or type B complex) is uncertain. At high uranyl concentrations, uranyl polymerizes at the surface of ferrihydrite giving, for instance, tris-uranyl surface complexes with and without carbonate. The similarities and differences between U(VI) adsorption by goethite and ferrihydrite are discussed from a surface structural point of view.     

Determining water requirements for Black Box (Eucalyptus largiflorens) floodplain woodlands of high conservation value using drip-irrigation

Black Box (Eucalyptus largiflorens F. Muell.), is a keystone tree species of lowland semi-arid floodplain ecosystems in south-eastern Australia. E. largiflorens woodlands are of high conservation value and threatened by climate change-induced drought and irrigation water diversions due to their location on upper floodplain areas where flood frequency has declined. Water requirements of E. largiflorens have not been well quantified using empirical data. Accordingly, knowledge gaps exist in relation to volumes of environmental water required to maintain and improve ecological condition for disconnected floodplain woodlands. To further assist conservation and water resource management, we tested the use of drip irrigation to provide a variety of water regimes to experimental plots in order to monitor tree responses. Water was provided via irrigation delivery across four regimes representing known volumes of water, referred to as an environmental water provision, applied over a 22-week period for two Austral summers. Benefits to trees were identified by measuring transpiration and plant water status using sap flow sensors and a Scholander pressure chamber, respectively. Results indicate that volumes of 0.3, 0.4, 0.7 and 0.8 ML increased transpiration and improved plant water status in comparison to a control, with delivery recommended to commence early autumn. Greater volumes (1.4 ML), substantially increased transpiration and improved water status, especially when delivered at a rate of ~25 mm week⁻¹ compared to a monthly 'burst' which broadly represented natural, sporadic summer rainfall in the region. For an environmental watering provision of 25 mm week⁻¹, ~178 ha of E. largiflorens woodland can be watered with a 1 GL environmental water allocation. The study methods presented are relevant worldwide and our results further the collective understanding of the benefits environmental water provides to E. largiflorens.     

Data model for system conceptualization in groundwater studies

Development of a conceptualization of a hydrogeologic system serves as the basis of groundwater modeling. While existing groundwater data models are designed to store groundwater system information, none is designed to capture its conceptual view. This study addresses this need by presenting a new object-oriented Conceptualization Groundwater Data Model that represents a groundwater system as a series of aquifer layers with defined aquifer properties and water boundary conditions. A case study is presented that develops the conceptual view of the groundwater system beneath Konza Prairie. This single conceptualization is used to support groundwater models across existing technologies of finite difference, finite element, and analytical element methods. While the models each employ different mathematics, data input files, and formats, all models are founded on the same conceptualization process that is represented using this new data model. The case study illustrates the data model's promise as an effective mechanism for groundwater system conceptualization and data storage, and utility for various groundwater computational models. This conceptualization of a groundwater data model suggests a new focus on incorporating system conceptualization into data model design.     

Is there more to eels than slime? An introduction to papers presented at the ICES Theme Session in September 2006

The following 15 papers in this issue of the ICES Journal ofMarine Science are based on presentations given at a Theme Session—"Isthere more to Eels than Slime?"—at the ICES Annual ScienceConference held in Maastricht, the Netherlands, during September2006. International involvement in research on the Europeaneel (Anguilla anguilla) started in 1968, when a draft synopsisof eel biology, fisheries, and aquaculture was prepared at theEuropean Inland Fisheries Advisory Commission (EIFAC) sessionin Rome. By 1975, an ICES Eel Working Group had been set up(WGEEL), and it met in Copenhagen to document information oneel populations and fisheries and, for the first time, to notedeclining trends in catches. These were the subjects of a jointEIFAC/ICES symposium in Helsinki in 1976, where mitigation byrestocking was first proposed,     

Fundamental Problems in Astrophysics

Progress of modern astrophysics requires the access to the electromagnetic spectrum in the broadest energy range. The Ultraviolet is a fundamental energy domain since it is one of the most powerful tool to study plasmas at temperatures in the 3,000–300,000 K range as well as electronic transitions of the most abundant molecules in the Universe. Moreover, the UV radiation field is a powerful astrochemical and photoionizing agent.The objective of this review is to describe the crucial issues that require access to the UV range. A summary has been added to the end with a more classic view of UV needs by astronomical object type; this approach is followed at length in the rest of the contributions of this issue.     

Escherichia coli strains harvested from springs in Kampala,Uganda: cell characterization and transport in saturated porous media

We hypothesized that the transport of Escherichia coli strains harvested from springs could be characterized by a similar set of cell characteristics and transport parameters. The hypothesis was tested by sampling springs throughout the Lubigi catchment in Kampala, Uganda. Chemo‐physical parameters in addition to total coliform concentrations were determined. Furthermore, E. coli strains were harvested, and cell properties determined. Column experiments in saturated quartz columns of 7 cm height were conducted to determine transport parameters of selected E. coli strains. Using a two‐site non‐equilibrium sorption model, transport was modelled by fitting breakthrough data in HYDRUS 1D. Results indicated faecal contamination of the springs with high concentrations of total coliforms, chloride and nitrate. Furthermore, the maximum relative E. coli concentrations (C/C₀)_max in the column experiments were high. Compared with our previous work on E. coli strains, collected from a pasture and from zoo animals, attachment was low. Modelling revealed that both equilibrium and kinetic sorption were not important under conditions employed in the experiments. These observations are explained by the way in which the strains were harvested: from termination points of flow lines (springs). Such strains may possess characteristics that might have influenced their transport in the subsurface leading to their low attachment efficiency and possibly contributing to the lack of influence of equilibrium and kinetic sorption characteristics. There was no significant correlation between cell properties and transport parameters. Furthermore, 58% of the tested strains were of the O21:H7 serotype, and all definable serotypes identified were associated with diseases. We speculate that this serotype may possess characteristics that allow preferential transport through the aquifers of the area. We demonstrated that bacteria harvested from termination points of flow lines compared with those obtained from pollution sources, which have not undergone transport yet, present a good option for the assessment of bacteria transport characteristics in aquifers. Copyright © 2013 John Wiley & Sons, Ltd.