The impact of discharge change on physical instream habitats and its response to river morphology

The impact of climate-induced discharge change on fish habitats, based on 1951–2008 time series, was investigated within the crystalline catchment of the Grosse Mühl River in Northern Austria. A significant trend change of air temperature, based on Mann–Whitney statistical testing, was recorded for spring 1989 (P?=?98.9 %) and summer 1990 (P?=?99.9 %). This led to a pronounced increase in summer low flow periods. Hydrodynamic-numerical (one-dimensional/two-dimensional) modelling was applied to simulate the changing habitat characteristics due to decreasing discharge in relation to various morphological patterns (riffle-pool/plane-bed reaches). Using bathymetric data, which were sampled on cross sectional measurements, we clearly determined that plane-bed reaches (featureless bed forms) are sensitive to climate-related, reduced discharge, whereas riffle-pool reaches continued to exhibit suitable physical fish habitats even under extreme low-flow conditions. The impact of the decreased summer discharge on instream habitats was strong for subadult and adult grayling which have been used as target fish species. In situ measurements in microhabitats (velocity/depth) revealed habitat suitabilities. These values were taken as biotic input for habitat evaluation on the micro scale. The findings clearly show that river morphology is a decisive parameter in terms of habitat preservation and restoration in the context of the future impacts of climate change (decreased discharge).     

Untersuchungen über die Bildung von Analcim aus natürlichen Silikaten

Zusammenfassung Im Temperaturbereich zwischen 100–180° C wurde experimentell die Umwandlung einiger natürlicher Silikate und silikatischer Gesteine in Analcim untersucht. Der Analcim bildete sich im alkalischen Milieu nach Abbau der einzelnen Ausgangssubstanzen direkt und ohne das Auftreten irgendeiner Zwischenphase. Die Entstehung des Analcims zeigte sich dabei abhängig von der Art und der Konzentration der einwirkenden Lösungen, von der Temperatur und von den Ausgangssubstanzen. Bei geringeren Konzentrationen der Lösungen war die Reaktion bedeutend langsamer als bei größeren. Der Analcim bildete sich nur in einem bestimmten Konzentrationsbereich der alkalischen Lösungen, wobei dieser für die einzelnen Substanzen unterschiedlich war. In Abhängigkeit von der Ausgangssubstanz entstanden bei geringeren Alkalikonzentrationen an Stelle des Analcims Zeolithe und bei größeren Alkallkonzentrationen SiO₂-Mineralien.

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Investigations on the formation of analcite from natural silicates

The transformation of some natural silicates and silicatic rocks into analcite was experimentally investigated over a temperature range of 100° C to 180° C. Analcite was directly formed in alkaline surroundings after reduction of the various starting substances without any intermediate phases. The formation of analcite depended on the kind and concentration of the reacting solutions, on the temperature and on the starting substance. At lower concentrations of the solutions the reaction was considerably slower than at higher ones. Analcite was formed only within a certain concentration range of the alkaline solutions, this range being different for the different substances. Depending on the starting substance, zeolites were formed at lower alkali concentrations. At higher alkali concentrations SiO₂ minerals were formed.

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Herrn Prof. Dr. H. Heritsch danke ich für sein dauerndes Interesse an dieser Arbeit, für Ratschläge und kritische Bemerkungen sowie für die Zurverfügungstellung der Mittel des Institutes für Mineralogie und Petrographie der Universität Graz.

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Herrn Prof. Dr. C. W. Correns möchte ich auch an dieser Stelle für die Möglichkeit, die experimentelle Technik in Göttingen kennenzulernen, meinen Dank sagen.     

Étude expérimentale des transformations de phase dans un gradient thermique : application au granite de Soultz-sous-Forêts,France

The circulation of an injected fluid in the deep granite of the Soultz-sous-Forêts HDR (‘Hot Dry Rock’) site causes important textural and mineralogical modifications. In order to determine the potential crystallization sequences along the fluid pathway, several experiments under thermal gradient were conducted at 600 bar (between 300 and 200 °C). After 40 days, the observed sequences of the newly formed products along the thermal gradient are always as follows, from high to low temperatures: quartz, feldspars, and finally interstratified clays, this implying a significant mobility of aluminium in the solution. To cite this article: A. Baldeyrou et al., C. R. Geoscience 335 (2003).     

Comparison of Mathematical Methods of Potential Modeling

Various attempts are known to turn the “catalogue” of mineral deposit models compiled by Cox and Singer (1986) operational, and have initiated activities called “potential mapping”, “potential modeling”, or “targeting”. The common ultimate objective is to estimate the probability for a given location that a mineralization of a given type occurred. The mathematics range from “weights of evidence” and others featuring a Bayesian approach to logistic regression by maximum likelihood, and include other realizations by means of fuzzy methods, genetic programming, and artificial neural nets. Once developed and coded, applications are not restricted to mineral prospection and exploration but include any kind of occurrences and their estimated probabilities, e.g., risk assessment of land slides and many others.     

Geochemical study on a well in the Western Canada Basin: relation of the aromatic distribution pattern to maturity of organic matter

Thirty-one rock samples from a Western Canada Basin well have been analysed for aromatics, using glass capillary gas chromatography with simultaneous flame ionization and sulfur-selective flame photometric detection. A uniform aromatic distribution pattern with a marked predominance of di- and tricyclic aromatic hydrocarbons was observed throughout a depth interval of 3000 meters comprising Cretaceous and Jurassic sediments. The very high relative abundance of sulfur aromatics at two narrow intervals in the Triassic and Mississippian is attributed to a major change in facies. Gradual changes with increasing depth have been observed for a series of compound ratios, which had been calculated from the isomers of methyl- and dimethylphenanthrene, and their parent compounds. These changes reflect the increasing thermal maturation of the sedimentary organic matter. A Methylphenanthrene Index (MPI) has been introduced, which exhibited a very good correlation with vitrinite reflectance data. The MPI is the first maturity parameter which is based on a series of aromatic hydrocarbons. This hydrocarbon internal maturity parameter permits the recognition and definition of maturity levels in extracts which can be compared to the maturity (e.g. vitrinite reflectance) of source rocks.     

Shock effects in MgAl2O4-spinel

Shock recovery experiments on synthetic MgAl₂O₄-spinel samples in the pressure range 25.5 to 50.5 GPa have been performed in order to examine the effects of shock waves on this material. The shocked samples were subsequently studied in the transmission electron microscope. All samples showed shock-induced dislocations with the Burgers vector 1/2 〈110〉 and twin lamellae of the twin-law {111}. In addition, samples, which had experienced the higher pressures, showed lamellar areas of a crystalline phase that we have not yet been able fully to characterize. It is probably not ε-MgAl₂O₄.     

Crystallization and age of zircon from Corsican ophiolitic albitites: consequences for oceanic expansion in Jurassic times

In Corsica, albitites and albite-granites are considered to be the latest products of an ophiolitic magma. Two albitites have been selected for a study of the morphology, typology and age of their zircons, applying for the first time the U-Pb method to Western Tethyan ophiolites. Both samples come from the Rospigliani series, possibly formed in a transform fault zone. The first one shows a cumulate texture, whereas the second has features indicative of more rapid cooling. Zircons have precipitated at the end of the fractional crystallization process after a strong enrichment in alkali and incompatible elements. In a typological diagram they plot at high temperature and high agpaicity indexes. These abundant large, euhedral to subhedral zircons, sometimes with fine zoning, may also contain inclusions of granitic composition which testifies to K fractionation in ophiolitic magmas. The U-Pb age of 161±3Myr is in the range of the ages obtained for Alpine and Apennines ophiolites. All these ophiolitic remnants belonging to the Liguro-Piedmont Basin may represent a portion of the Central Atlantic Ocean created during Middle and Upper Jurassic times.