Iron-mediated oxidation of antimony(III) by oxygen and hydrogen peroxide compared to arsenic(III) oxidation

Antimony is used in large quantities in a variety of products, though it has been declared as a pollutant of priority interest by the Environmental Protection Agency of the United States (USEPA). Oxidation processes critically affect the mobility of antimony in the environment since Sb(V) has a greater solubility than Sb(lll). In this study, the cooxidation reactions of Sb(lIl) with Fe(ll) and both O2 and H2O2 were investigated and compared to those of As(III). With increasing pH, the oxidation rate coefficients of Sb(lll) in the presence of Fe(ll) and O2 increased and followed a similar pH trend as the Fe(ll) oxidation by O2. Half-lives of Sb(lll) were 35 and 1.4 h at pH 5.0 and pH 6.2, respectively. The co-oxidation with Fe(ll) and H2O2 is about 7000 and 20 times faster than with Fe(ll) and O2 at pH 3 and pH 7, respectively. For both systems, *OH radicals appear to be the predominant oxidant below approximately pH 4, while at more neutral pH values, other unknown intermediates become important. The oxidation of As(lll) follows a similar pH trend as the Sb(lll) oxidation; however, As(lll) oxidation was roughly 10 times slower and only partly oxidized in most of the experiments. This study shows that the Fe(ll)-mediated oxidation of Sb(Ill) can be an important oxidation pathway at neutral pH values.     

Indikatorenbasierte Evaluierung von Fischhabitaten in alpinen Fließgewässern

The EU Water Framework Directive commits member states to achieve good ecological status in all waterbodies. Artificial or heavily modified waterbodies must reach at least its good ecological potential. In view of these requirements, simple and feasible methods are required in order to evaluate habitat suitability for relevant target species in larger river reaches. Well-developed models for determining the relationship between stream flows and habitat for target species mainly based on micro- and meso-scale already exist. However, the application of such models is complex and time-consuming and consequently limited to relatively short river segments. The objective of this study is to develop a simplified applicable assessment model to evaluate habitat conditions for selected target fish. This model uses hydro-morphological indicators for the habitat assessment and relies on correlative relations between habitat suitability and hydro-morphological features of river stretches (average Froude-number, relative flow width, mean bed slope, relative water depth and flow velocity). The indicators were determined as reach-related averages, derived from 2D model simulations (hydraulic and habitat-specific). Particular emphasis was laid on using a wide range of river stretches with different hydro-morphological characteristics (hydrology, bed substratum, bed structures, degree of braiding, sinuosity of the river course, mean bed width and bed slope). As a result, a set of model equations enables the evaluation of fish habitat conditions in river stretches as a function of flow and morphology. The habitat suitability assessment focuses on four preselected target species: brown trout, European grayling and for low slope rivers common nase and barbel.     

Mixed crystalline films of co-evaporated hydrogen- and fluorine-terminated phthalocyanines and their application in photovoltaic devices

Blends of organic electron and hole conductive materials are widely used for ambipolar charge carrier transport and photovoltaic cells. An obvious choice for donor–acceptor blends are organic semiconducting materials in their hydrogenated and fluorinated form, since they combine potentially suitable electronic properties with structural compatibility of the two constituents. This study focuses on the structural, optical, and electrical properties of blends using hydrogenated copper-phthalocyanine (H₁₆CuPc) in combination with its per-fluorinated version (F₁₆CuPc). Using X-ray scattering, scanning force microscopy and optical absorption measurements we show that mixed crystalline films are obtained by co-evaporation of the two materials. Electrical transport measurements reveal a profound reduction of the current for bipolar charge injection in mixed films. We discuss the formation of self-trapped charge transfer excitons as possible explanation for this unexpected behaviour, which impedes the usability of this system in photovoltaic cells.     

Evaluation of the origin of nitrate influencing the Klju? groundwater source, Serbia

This paper describes the use of the dual isotope method involving δ(15)N and δ(18)O measurements of dissolved nitrates to assess the origin and fate of groundwater nitrate at the Klju? groundwater source, Serbia. A sampling campaign was conducted in September 2007 during flow conditions obtaining groundwater from observation wells and river water fed by a shallow aquifer hosted in alluvial (sandy-gravel) sediments. Nitrate isotope ratios ranged from +5.3 to +16.9‰ and δ(18)O(NO(3)) values varied from -2.3 to +5.0‰. Two major contamination sources were identified with isotopic compositions characteristic for nitrate derived from nitrification of soil organic nitrogen (+5.3 to +7.8‰ for δ(15)N) resulting in nitrate concentrations of 33.6 and 78.8 mg/L and nitrate derived from animal wastes or human sewage, e.g. via septic systems, yielding δ(15)N values of +9.9 to +11.9‰ and elevated nitrate concentrations of 31.2-245.8 mg/L. The occurrence of nitrification and denitrification was also revealed based on concentration and isotope data for dissolved nitrate.     

Optimierung von Wasserkraft und Ökologie bei Erneuerung oder Revitalisierung bestehender Anlagen – „win-win“-Ansatz

In Austria, using hydropower has a centuries-long tradition. Whereas we first placed mills along our rivers to put water’s power to use, today we have over 5,200 water power stations of various types, from the smallest facilities to pumped-storage hydroelectric plants in the Alps. Today, water power accounts for roughly 60 % of our domestic power production, though the various types of power stations used have diverse ecological effects. This article presents a “win-win” approach to improving both hydropower production and ecological outcomes on the basis of the Kamp River in Lower Austria. The Kamp is not only home to a pumped-storage hydroelectric plant and the major plants Ottenstein, Dobra-Krumberg and Thurnberg-Wegscheid, but also to 14 smaller plants with turbines that are between 25 and 75 years old, many of them with energy conversion efficiency ratios of well under 0.7. Using the case study of a small water power plant, the chances of achieving a win-win situation are presented in detail. In this context, replacing the turbines is a major aspect of improving these plants. Extensive analyses have demonstrated that balanced planning approaches can yield both higher efficiency and better conditions for aquatic ecology, thanks to increased residual flows. Further, energy calculations and numerical habitat simulations have confirmed that a win-win situation is feasible for the small power plant studied, especially if Kaplan turbines are used. For example, they show that, despite the increased residual flow of up to 800 l/s, a considerable performance increase over the status quo is possible (maximum performance increase of 17 % without considering residual flow). If the residual flow was only 400 l/s, which tests indicate would mean an improvement in the habitat conditions for all ages of the dominant fish species (the brown trout) of > 50 %, a performance increase of 8 % would be the result. Thanks to the generally applicable methodology used, the win-win approach presented here can broadly be used in the optimization, efficiency improvement and revitalization of current hydropower plants, producing both more electricity and higher residual flow levels to improve local ecological conditions. In order to make this win-win situation a reality, innovative and integrative financial models for e.g. new turbines related to the fields of green energy production and environmental protection will be essential.     

Abiotic Characterization of Brown Trout (Salmo trutta f. fario) and Rainbow Trout (Oncorhynchus mykiss) Spawning Redds Affected by Small Hydropower Plants — Case Studies from Austria

Salmonid rivers in Austria are considerably regulated by small hydropower facilities, resulting in potential declines of the spawning habitats of salmonids. To assess the restrictions and possible quality of hydropower‐influenced river sections for salmonid, spawning redd densities of brown trout and rainbow trout were monitored in two rivers in 2014 and 2015. The results showed spawning close to small hydropower facilities for both investigated species — with similarities in redd characteristics like pit and tail length. Differences occurred concerning the distance of redd construction to the next shore. Brown trout spawn close to the banks in comparison to rainbow trout which use the entire active channel width. In addition to the preference of brown trout for certain cover types, it turned out that the presence of high quality spawning gravel in the river is the dictating abiotic variable (probably bottleneck) in the control of salmonid populations even for river reaches impacted by small hydropower plants. Moreover, the assessments of spawning redd densities enabled a discussion of different opportunities for spawning habitat enhancement of salmonids in river sections regulated by small hydropower facilities. Here, in conclusion, it was found that the fill‐up of the backwater sites by transported sediments or the structural modification (e.g. boulder placement) in the tail of the backwater could improve the spawning situation in a sustainable way. Copyright © 2016 John Wiley & Sons, Ltd.     

Atomic force microscopy and Raman scattering studies of femtosecond laser-induced nanohillocks on CR-39

The phenomenon of nanohillock-like defect formation on the surfaces of CR-39 by ultra-short laser irradiation is investigated using an Atomic Force Microscope (AFM) and Raman Scattering. A polymer CR-39 target was exposed to Ti:sapphire 25-fs laser pulses with a central wavelength at 800 nm. Samples were irradiated for different laser fluences both in air and vacuum. Detailed surface topographical features of the bombarded samples were characterized by atomic force microscopy in contact mode in air at room temperature. AFM reveals that the growth of nanohillocks and their features are strongly dependent on the ambient condition, target position from focus, and irradiation fluence. The appearance of these nanohillocks in the range 1–20 nm in height and 10–90 nm in diameter are regarded as typical features for fast electronic processes (correlated with existence of hot electrons) and are explained on the basis of Coulomb explosion. These nanostructures due to localization of laser energy deposition in small areas provide a possible pathway from dense electronic excitation to atomic motion causing permanent structural modification which are well correlated to structural alterations, like crosslinking and chain scissions, inferred from Raman spectroscopy.     

Instability during cohesive zone growth

Tensile microcracking of quasi-brittle materials is studied by means of micromechanics, based on (i) an elasto-damaging cohesive zone model accounting for cohesive softening and (ii) a dilute distribution of non-interacting microcracks of uniform orientation and size. Considering virgin microcracks (initially without cohesive zones), macroscopic tensile load increase results in growth of cohesive zones ahead of stationary (non-propagating) cracks and, subsequently, in crack propagation which, notably, will be encountered before the cohesive zones are fully developed i.e. onset of instable cohesive zone growth will be encountered at a load level (i) at which tractions are still transmitted across the inner edges of the cohesive zones and (ii) at which the separation at the inner edges of the cohesive zones is smaller than its critical value. Focusing on onset of instable cohesive zone growth, the chosen approach allows for accessing quantities characterizing the stability limit (e.g., the intensity of the macroscopic loading and the opening at the inner edges of the cohesive zones), without raising the need for non-linear Finite Element analyses. It is shown that the tensile macrostrength of materials containing virgin microcracks is larger than the one related to cracks with already initially fully developed cohesive zones, and related strength differences are quantified for a wide class of cohesive softening behavior. The proposed model is validated by comparing model predictions with an exact solution (available for the special case of constant cohesive tractions) and with results from reliable Finite Element analyses. The paper will be of interest for engineers involved in testing and/or in modeling of quasi-brittle media including cementitious materials and rock.