Impact of channel bar form and grain size variability on estimated stranding risk of juvenile brown trout during hydropeaking

Hydropeaking leads to artificial fluctuations in discharge and corresponding water levels with pronounced dewatering areas between base and peak flow along gravel bars and channel banks. In the present study, 16 hydropeaking reaches in Austria were investigated to assess possible differences in the estimated stranding risk for young of the year brown trout according to different gravel bar types and differences in microtopography roughness. Based on hydrodynamic‐numerical modelling, a predictive habitat modelling approach was implemented in the study design. Accompanied by grain size sampling along the various channel bars, a conceptual stranding risk model (SRM) was developed. The results showed that a high variability in estimated stranding risk exists for the tested sites considering discharge ratios of 1:3, 1:5 and 1:10. With respect to the discussion of establishing legal thresholds for ramping ratios in discharge, it was documented that, exemplarily, a discharge ratio base flow/peak flow of 1:5 (winter base flow conditions) could cause minor differences in the spatial extent of dewatering areas and the related estimated stranding risk for juvenile brown trout compared to a ratio of 1:2 for summer base flow conditions. Microtopographic roughness was addressed due to sampling and analysis of grain size distributions. Statistical testing of grain size distributions revealed significant differences between the surface material compositions of the investigated gravel bars. Those differences are evident, particularly for the coarser fraction (d₉₀), which is important as cover for young of the year brown trout. These aspects of grain size in habitat use and hydraulics have been addressed in the conceptual SRM. The results showed that point bar morphology, in particular, was less sensitive to the risk of stranding compared to, for example, alternating gravel bars. Considering the multiple pressures for alpine rivers, the improvement of structural features due to bar formation and related self‐forming processes is discussed as a possible alternative for future mitigation measures to reduce the negative impacts of hydropeaking. Copyright © 2014 John Wiley & Sons, Ltd.     

Revision of the Clam Shrimp Genus Magumbonia from the Upper Jurassic of the Luanping Basin,Hebei,Northern China

The diverse clam shrimp Nestoria-Keratestheria fauna is widely distributed in the Dabeigou Formation in northern Hebei and eastern Inner Mongolia of China.Its important component genus Magumbonia from the Dabeigou Formation in the Luanping Basin,northern Hebei,China,is revised on the basis of a scanning electron microscope (SEM) examination of the type species M.jingshangensis Wang,1984,which revealed morphological features not recognized previously.These include coarse reticulation on the umbo and promi...     

Sediment loads and processes in large rivers

<正>The pressure and impact on large rivers have increased greatly in recent years,as a consequence of their exploitation to meet various human needs.Large rivers are particularly exposed to problems of multiple uses,often with conflicting aims.At the global scale river systems are increasingly altered by dams,leading to interruption of continuity and a disrupted sediment regime,which results in far-reaching problems.These challenges point also to the need for more integrated management approaches and consideration of catchment-river interactions emphasizing land use management and effects of these uses.At the global scale,there is currently no overview assessment of the current status of the world's large rivers,the conflicting demands on such rivers,and likely future anthropogenic impacts,as well as the potential for restoration,improvements in integrated management and the associated problems caused by their multiple uses.The special issue in the International Journal of Sediment Research on"Sediment loads and processes in large rivers"aims to provide a global forum for a wide-ranging discussion of key issues related to research on large rivers and to their effective and sustainable management,involving both scientists and decision makers.The sequence of papers in the special issue highlights the current situation in different river systems with regard to morphodynamic reactions of     

Physical model experiments for sediment supply to the old Rhine through induced bank erosion

A mobile-bed, undistorted physical model （1：40） has been used to investigate different sediment supply strategies to the Old Rhine through bank protection removal and modifications of groyne dimensions and configuration, which cause bank erosion. This trained channel was previously the main bed of the upper Rhine downstream of Basel （Switzerland）, but it has an artificially low flow regime since the construction of the Grand Canal d＇Alsace, a navigation canal, and a flow control dam at Kembs （France）. Training works and subsequent channel incision have also greatly reduced sediment transport rates and created a heavily armoured bed. The modelled pilot site has a groyne field on the left bank. Results show that the currently existing groynes at the site are not effective in creating high bank-side velocities conducive to bank erosion, even for flow rates significantly higher than the mean annual flow rate. The river bank has also proved to be more resistant than previously thought, allowing long stretches of bank protection to be safely removed. The physical model testing process has produced a new configuration for the groyne field, where two higher, larger island groynes are placed further apart than the three existing attached groynes. This innovative approach has proved effective, causing bank erosion for flow rates below the mean annual flow rate, with consistent erosion being observed. It has also been found that such a configuration does not pose a hazard for the Grand Canal d＇Alsace, which is situated next to the Old Rhine, through excessive bank erosion during high flow events.     

Increasing levels and biomagnification of persistent organic pollutants (POPs) in Antarctic biota

Representatives of the Antarctic food web (krill, cephalopod, fish, penguin, seal) of the area around Elephant Island and from the Weddell Sea were analysed for the most recalcitrant organochlorine compounds. Due to sorption of the compounds to sinking particles and accumulation in sediments, two benthic fish species (Gobionotothen gibberifrons, Chaenocephalus aceratus) feeding on benthos invertebrates and fish reflected significantly increasing concentrations within a decade (1987-1996), while a benthopelagic species (Champsocephalus gunnari) feeding on krill did not. In the pelagic food chain, lipid normalised concentrations of all compounds increased from Antarctic krill to fish proving that biomagnification of highly lipophilic pollutants (log octanol-water partition coefficient>5) occurs in water-breathing animals. As top predators Weddell and southern elephant seals (Leptonychotes weddellii, Mirounga leonina) biomagnified the persistent organic pollutants relative to krill 30-160 fold with the exception of hexachlorobenzene, the levels of which were lower than in fish indicating its intense specific elimination.     

Active Galactic Nuclei

F11 Jets, supernovae, gammabursts – more light for theory? F35 A Direct Comparison of the QSO Samples from VPMS and SDSS F36 Gravitational Microlensing Simulations and Ensemble Broad‐Band Variability of the QSOs from VPMS F42 Luminosity function of low redshift quasars F43 Star Formation around Active Galactic Nuclei – Results from near infrared observations F58 High‐Redshift Quasars as Probes of Early Star Formation F66 On the dust emission of Seyfert nuclei F72 Propagation of Very Light MHD Jets F78 Giant Outflows in MassiveHigh‐z Radio Galaxies: Direct Evidence for AGNFeedback in the Early Universe F89 Lowfrequency mapping of ‘normal’ FR II radio galaxies: Resolving the puzzle of X‐shaped radio sources F90 Nature of X‐shaped radio sources: A statistical approach F100 Cosmological growth of Supermassive Black Holes: constraints on kinetic and radiative energy feedback F107 Molecular Tori in AGN F136 Electron‐Ion Recombination Rate Coefficients of Iron M‐Shell Ions for X‐Ray Astronomy F139 Hydrodynamic models of obscuring tori F145 The unique BL Lac Object S5 0716+714 F158 On the Cluster Environment of the BL Lac Object OJ 287 F179 The circumnuclear dust in nearby AGN resolved by mid‐infrared interferometry F184 NIR‐imaging of SDSS BL Lac objects F190 Blazar Observations in the TeV energy range with the MAGIC Telescope F198 Gas Inflow Rates in Nearby AGN Galaxies F202 Two zone SSC model for blazar jets F215 Long‐termVHE γ ‐ray monitoring of bright blazars with a dedicated telescope F218 Long termmonitoring of bright TeV Blazars with the MAGIC telescope F220 Fifteen Blazars in Very‐High Energy Gamma Rays: A Comparative Study F229 Numerical calculation of blazar spectra. Application to 1 ES 1218+30.4 F230 Blazar spectral energy distributions corrected for gamma ray attenuation F240 Observation of PG 1553+113 with the MAGIC Telescope F243 VHE Gamma‐Ray Flare of PKS2155‐304 detected by the MAGIC telescope F245 Observations of 3C279 with the MAGIC Telescope F258 Diffraction limited near infrared imaging spectroscopy of the NLR of NGC4151     

Effects of natural attenuation processes on groundwater contamination caused by abandoned waste sites in Berlin

The aim of this research project is to identify, characterize and quantify natural attenuation (NA) processes in groundwater affected by emissions of abandoned waste disposal sites in Berlin-Kladow/Gatow, Germany. It is part of the funding priority called KORA established by the Federal Ministry for Education and Research (BMBF) to explore the extent to which NA can be used for remedial purposes for varied forms of soil and groundwater contamination. Information on the emission behaviour of individual parameters is generated on the basis of hydrogeochemical comparison of 20 years old and new data. Using groundwater-modelling and CFC-analysis, information on the transport and retention of pollutants in groundwater is compiled. The microbial colonization of contaminated aquifers is characterized by molecular biological methods [polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE)] to differentiate between contaminated and not contaminated zones.     

Leaching and differential recrystallization of metamict zircon under experimental hydrothermal conditions

We report results of hydrothermal experiments on four alluvial zircons from Sri Lanka, which cover a wide range of radiation damage, at 450 °C and 1.3 kbar for 744 h with 2 M CaCl₂ solution as reactive fluid. After the hydrothermal treatment, the most metamict samples show micrometer-thick reaction rims, which surround apparently unreacted zircon, as revealed by cathodoluminescence (CL) and Nomarski differential interference contrast (NDIC) images. These rims have sharp, curved, and transgressive boundaries with unreacted zircon and are, in some cases, spread out along cracks. The thickness of reaction rims increases with increasing cumulated !-dosage of the starting materials. The reaction rims are strongly enriched in Ca (up to 7000 ppm) and a water species and depleted in radiogenic Pb, Zr, and Si, as revealed by electron microprobe analyses. A significant Th loss from the reaction rims was detected in the case of the most metamict sample, whereas U remained in the structure. FT-infrared spectrometry and X-ray diffraction measurements revealed that the bulk run products were recrystallized. Using micro-Raman spectrometry, we were able to demonstrate that differential recrystallization took place. The reaction rims are strongly recrystallized, whereas the unreacted grain interiors underwent only minor recrystallization. Recrystallization of the rims is accompanied by an enhancement of the integral CL intensity. It is suggested that recrystallization in the reaction rims was catalyzed by water infiltration and ion exchange and prevented significant congruent zircon dissolution under the given experimental conditions. Previous zircon studies have shown that (1) a transgressive morphology, (2) a reduced Th-U ratio, and (3) an enhanced CL emission are also characteristics of rims in zircons from high-grade metamorphic rocks. Based on these similarities between natural and experimentally produced rims, it is suggested that leaching-catalyzed recrystallization is an important alteration process in zircon under wet geological conditions and can account for many complex core-rim structures found in natural zircons. Furthermore, the strong enrichment of Ca in the reaction rims supports previous assumptions that high Ca concentrations in natural zircons are of secondary origin. It is suggested that lower U-Pb concordia intercept ages obtained from single-phase zircons with high Ca contents date a leaching event.