Self‐purification in Upland and Lowland Streams

Ecological investigations at four streams in Saxony‐Anhalt have shown that there are considerable differences between the self‐purification power of upland and lowland streams. This result is reflected in chemistry and in microbiology. The structure of the bottom substrate mainly influences the degree of self‐purification in connection with rate of flow and flow velocity. The results and differences are demonstrated using the example of Katzsohlbach in the landscape unit “Mittel‐ and Unterharz” and the stream Olbe in the landscape unit “Magdeburger Börde”.     

Genetic relationship between silver–lead–zinc mineralization in the Wutong deposit,Guangxi Province and Mesozoic granitic magmatism in the Nanling belt,southeast China

More than 50 % of the world's total reserves of tungsten are in China and most tungsten deposits are located in the Nanling range in southeast China. This study explores the potential genetic relationship between tungsten–tin (W–Sn) mineralization and shallower Ag–Pb–Zn deposits in the Nanling range based on data from the Wutong deposit, Guangxi Province. The lead, oxygen, carbon, sulfur, and strontium isotopic compositions of minerals at Wutong indicate that a single crustal-derived fluid was responsible for mineralization. Wutong likely formed at relatively low temperatures (～200–300 °C) and low pressures, as indicated by the similarity between homogenization temperatures of fluid inclusions and those estimated from S isotopic compositions of minerals. The hübnerite age (92.3–104.4 Ma) indicates that the Wutong mineralization is likely related to nearby Late Yanshanian (Cretaceous) S-type granites derived from Proterozoic crust. This mineralization event coincides with the last W–Sn mineralization event and the Cretaceous peak of mineralization in the Nanling range.     

Younger Dryas to mid-Holocene environmental history of the lowlands of NW Transylvania, Romania

Pollen, micro-charcoal and total carbon analyses on sediments from the Turbuta palaeolake, in the Transylvanian Basin of NW Romania, reveal Younger Dryas to mid-Holocene environmental changes. The chronostratigraphy relies on AMS ¹⁴C measurements on organic matter and U/Th TIMS datings of snail shells. Results indicate the presence of Pinus and Betula open woodlands with small populations of Picea, Ulmus, Alnus and Salix before 12,000 cal yr BP. A fairly abrupt replacement of Pinus and Betula by Ulmus-dominated woodlands at ca. 11,900 cal. yr BP likely represents competition effects of vegetation driven by climate warming at the onset of the Holocene. By 11,000 cal yr BP, the woodlands were increasingly diverse and dense with the expansion of Quercus, Fraxinus and Tilia, the establishment of Corylus and the decline of upland herbaceous and shrubs taxa. The marked expansion of Quercus accompanied by Tilia between 10,500 and 8000 cal yr BP could be the result of low effective moisture associated with both low elevation of the site and with regional change towards a drier climate. At 10,000 cal yr BP, Corylus spread across the region, and by 8000 cal yr BP it replaced Quercus as a dominant forest constituent, with only little representation of Picea abies. Carpinus became established around 5500 cal yr BP, but it was only a minor constituent in local woodlands until ca. 5000 cal yr BP. Results from this study also indicate that the woodlands in the lowlands of Turbuta were never closed.     

Temperature induced decoupling of enzymatic hydrolysis and carbon remineralization in long-term incubations of Arctic and temperate sediments

Extracellular enzymatic hydrolysis of high-molecular weight organic matter is the initial step in sedimentary organic carbon degradation and is often regarded as the rate-limiting step. Temperature effects on enzyme activities may therefore exert an indirect control on carbon mineralization. We explored the temperature sensitivity of enzymatic hydrolysis and its connection to subsequent steps in anoxic organic carbon degradation in long-term incubations of sediments from the Arctic and the North Sea. These sediments were incubated under anaerobic conditions for 24 months at temperatures of 0, 10, and 20 °C. The short-term temperature response of the active microbial community was tested in temperature gradient block incubations. The temperature optimum of extracellular enzymatic hydrolysis, as measured with a polysaccharide (chondroitin sulfate), differed between Arctic and temperate habitats by about 8-13 °C in fresh sediments and in sediments incubated for 24 months. In both Arctic and temperate sediments, the temperature response of chondroitin sulfate hydrolysis was initially similar to that of sulfate reduction. After 24 months, however, hydrolysis outpaced sulfate reduction rates, as demonstrated by increased concentrations of dissolved organic carbon (DOC) and total dissolved carbohydrates. This effect was stronger at higher incubation temperatures, particularly in the Arctic sediments. In all experiments, concentrations of volatile fatty acids (VFA) were low, indicating tight coupling between VFA production and consumption. Together, these data indicate that long-term incubation at elevated temperatures led to increased decoupling of hydrolytic DOC production relative to fermentation. Temperature increases in marine sedimentary environments may thus significantly affect the downstream carbon mineralization and lead to the increased formation of refractory DOC.     

Reverse time migration of CMP-gathers an effective tool for the determination of interval velocities

One of the most important steps in the conventional processing of reflection seismic data is common midpoint (CMP) stacking. However, this step has considerable deficiencies. For instance the reflection or diffraction time curves used for normal moveout corrections must be hyperbolae. Furthermore, undesirable frequency changes by stretching are produced on account of the dependence of the normal moveout corrections on reflection times. Still other drawbacks of conventional CMP stacking could be listed.One possibility to avoid these disadvantages is to replace conventional CMP stacking by a process of migration to be discussed in this paper. For this purpose the Sherwood-Loewenthal model of the exploding reflector has to be extended to an exploding point model with symmetry to the lineP _EX M whereP _EX is the exploding point, alias common reflection point, andM the common midpoint of receiver and source pairs.Kirchhoff summation is that kind of migration which is practically identical with conventional CMP stacking with the exception that Kirchhoff summation provides more than one resulting trace.In this paper reverse time migration (RTM) was adopted as a tool to replace conventional CMP stacking. This method has the merit that it uses the full wave equation and that a direct depth migration is obtained, the velocityv can be any function of the local coordinatesx, y, z. Since the quality of the reverse time migration is highly dependent on the correct choice of interval velocities such interval velocities can be determined stepwise from layer to layer, and there is no need to compute interval velocities from normal moveout velocities by sophisticated mathematics or time consuming modelling. It will be shown that curve velocity interfaces do not impair the correct determination of interval velocities and that more precise velocity values are obtained by avoiding or restricting muting due to non-hyperbolic normal moveout curves.Finally it is discussed how in the case of complicated structures the reverse time migration of CMP gathers can be modified in such a manner that the combination of all reverse time migrated CMP gathers yields a correct depth migrated section. This presupposes, however, a preliminary data processing and interpretation.     

Streams in the Harz National Parks (Germany) — a hydrochemical and hydrobiological evaluation

Between 1995 and 2001, 16 measuring points at small and medium sized brooks in the Harz National Parks were sampled. The samples have been evaluated by means of hydrochemistry and macroinvertebrate biology. Although nearly all streams are largely uncontaminated by oxygen-consuming substances, they are settled only by a small number of macroinvertebrate species. There is a clear correlation between this number and pH. The reduction in species number with decrease of pH is mainly caused by the absence of most Ephemeroptera, some Coleoptera and Trichoptera. Comparing biological evaluation of acidity with physico-chemical measurements, a unacceptable underestimation was found. The reason could be that different sensitivities to acidification between regional populations seem to exist.

Despite of the low species number, there is a very specific macroinvertebrate fauna that emphasizes the conservation value of the Harz National Parks.     

A new approach to simulating disorder in crystals

The technique of calculating lattice dissociation energies using static, minimum lattice energy, ionic models has been extended to allow for multiple occupancy of the ionic sites. A particular lattice site can have a fraction x of an ionic species A and a fraction y of an ionic species B, where the position of each can be relaxed separately along with the unit cell dimensions until an equilibrium is reached. Various degrees of long and short range order can be modelled. This technique has been applied to the mineral sillimanite, Al₂SiO₅, to calculate the effect on the lattice energy of (Al, Si) ordering over the tetrahedral sites. It is found using this method that (Al, Si) ordering with space group Pbmn stabilizes the material by 29.25 kcal/mol (Al^iv-O-Al^iv), with respect to the completely disordered material.     

Geoelektrische Untersuchungen zur Ermittlung der Blitzgefährdung

Zusammenfassung Aus den Untersuchungen, die vom Verf. in Oesterreich ausgeführt wurden, werden folgende Ergebnisse bewiesen: 1. Die elektrische Bodenleitfähigkeit beinflusst massgebend den erdnahen Teil der Blitzbahn; 2. Es gibt daher Zonen hoher Blitzgefährdung, die Blitznester genannt werden; 3. Die Scheitelstromstärke des Blitzes ist durch den spezifischen Bodenwiderstand mitbestimmt; 4. Es besteht ein Zusammenhang zwischen Blitzgefährdung und geoelektrischer Bodenbeschaffenheit.

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Summary Experiments carried out by the Author in Austria show the following results: 1. The electrical conductivity of the grounds has a decisive influence on the course of the lightning: such zones are called «lightning nests». 3. The amplitude of the strength of lightning current is determined also by the specific resistivity of ground. 4. The agreement between the position of lightning nests and the geoelectric condition of ground is beyond dispute.

     

Die geoelektrische Überprüfung von Zementinjektionen zur Verfestigung des Baugrundes

Zusammenfassung Um den Kluftraum im Baugrunde von Staumauern zu schliessen, presst man in diesen Zementmilch. Es wird nun ein geoelektrisches Verfahren beschrieben, mit dem folgende Angaben bestimmt werden können: Das offene Kluftvolumen vor der Injektion; das durch die Injektion gefüllte Kluftvolumen; die Menge von Injektionsmilch, die aus dem für die Injektion bestimmten Raume nach entfernten Räumen ausfloss. Das Verfahren wurde in Oesterreich an mehreren hundert Einzelinjektionen erprobt.

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Summary In order to close the clefts in subsoil of dams, cement is pressed into them. A geoelectrical method of measuring is now described, with which the following data may be determined: the open volume of the clefts before injection of cement, the volume that has been filled with cement during injection and the still open volume after injection. Further we can state, whether cement has flows to distant spaces. The method was esamined by some hundred injections in Austria.