Die Entstehung von Trübungszonen im Unterlauf der Flüsse,speziell im Hinblick auf die Verhältnisse in der Unterelbe

Zusammenfassung Im Unterlauf von Flüssen, welche dem Gezeiteneinfluß des Meeres ausgesetzt sind, finden sich häufig Zonen besonders hohen Trübstoffgehaltes. Diese Erscheinung findet ihre maximale Entfaltung dort, wo sich der Mischungsvorgang des Flußwassers mit dem Meerwasser durch das schwache Ansteigen des Salzgehaltes erstmalig zu erkennen gibt. Aus diesem Grunde glaubte man bisher annehmen zu müssen, daß das Auftreten der Trübungszone in erster Linie durch die im Experiment nachweisbare Ausflockung gelöster Kolloide durch den Ionengehalt des Meerwassers hervorgerufen würde, während dynamische Vorgänge hierbei nur eine untergeordnete Rolle spielen sollten. An Trübungsmessungen in Wasser von verschiedenen Punkten aus der Unterelbe wird wahrscheinlich gemacht, daß die Verhältnisse gerade umgekehrt liegen. Durch die eigenartigen Strömungs- und Vermischungsvorgänge in solchen dem Gezeiteneinfluß unterliegenden Ästuarien bildet sich eine Art Sinkstoff-Falle. Diese fängt die Trübungsstoffe aus dem Flußwasser in der Mischzone ab, indem sie diese in einem ständigen vertikalen Kreislauf herumführt, während das Wasser selbst ungehindert ins Meer abfließt. Der chemische Vorgang der Ausflockung dagegen scheint, wenn überhaupt, nur eine ganz untergeordnete Rolle bei der Ausbildung dieser Zonen zu spielen.

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On the development of turbid zones in the lower course of rivers with special consideration of conditions in the lower Elbe

Summary Zones with an extremely high degree of turbidity are of frequent occurrence in the lower course of rivers exposed to tidal influences of the sea. Their maximum development will be found in an area where the mixing process between river water and sea water first becomes perceptible from a slight increase in salinity. For this reason, it was believed that the presence of turbid zones should, in the first place, be attributed to the occurrence of dissolved colloids, a process that is caused by ion concentration of sea water the existence of which has been proved by laboratory experiments; dynamic processes were, however, believed to play only a subordinate part in the development of such turbid zones. Turbidity measurements in water taken from various places in the lower Elbe show that, in all probability, the reverse will be true. The peculiar water movement in such tidal estuaries form a sort of trap for suspended matter which catches the turbid matter from the river water in the mining zones and makes them revolve continuously in a vertical circulation while the water itself flows to the sea, without hindrance. The chemical process of precipitation seems, if at all, to exercise but little influence on the development of the turbid zones.

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Sur le développement des zones de turbidité dans les cours inférieurs des fleuves et particulièrement sur les conditions dans le cours inférieur de l'Elbe

Résumé Dans les cours inférieurs des fleuves soumis à l'influence des marées se trouvent souvent des zones de turbidité, dont le maximum se développe aux endroits où la faible augmentation de la salinité révèle, pour la première fois, le mélange de l'eau fluviatile avec l'eau de mer. Pour cette raison, on supposait jusqu'ici que la présence des zones de turbidité soit produit, en premier lieu, par suite de la précipitation de colloides dissous, par l'eau de mer, un phénomène dont l'existence est prouvée dans des expériments de laboratoire; aux procès dynamiques on n'attribuerait, sous ce rapport, qu'un rôle secondaire. Des observations effectuées à plusieurs échantillons d'eau recueillis à des endroits divers dans le cours inférieur de l'Elbe montrent, au contraire, que ce sont probablement des phénomènes dynamiques, auxquels il faut attribuer la présence des régions de turbidité. Les mouvements d'eau particuliers dans de tels estuaires à marée produisent une sorte de »piège de matières suspendues«. Ce »piège« attrappe les sédiments amenés par les fleuves et les engage dans une circulation verticale pendant que les eaux fluviatiles poursuivent sans entravement leur chemin vers la mer. Le procédé chimique de la précipitation ne semble donc exercer qu'une très faible influence sur la formation des zones de turbidité.

     

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Peridotitic mantle xenoliths from kimberlites on the Ekati Diamond Mine property, N.W.T., Canada: major element compositions and implications for the lithosphere beneath the central Slave craton

The composition, structure and thermal state of the lithosphere beneath the Slave craton have been studied by analysing over 300 peridotitic mantle xenoliths or multiphase xenocrysts entrained within kimberlites in the Lac de Gras area. These xenoliths are derived from seven kimberlites located on the Ekati Diamond Mine™ property and define a detailed stratigraphic profile through the central Slave lithosphere from less than 120 km down to 200 km. Two dominant peridotite types are present, namely garnet-bearing harzburgite and lherzolite with rare occurrences of chromite-facies peridotite, websterite and wehrlite. The pressures and temperatures (P–T's) defined by the entire data-set range from 28 to 62 kbar and 650 to 1250 °C, respectively, and approximately intersect the diamond stability field at 900 °C and 42 kbar. There is no apparent change in the geotherm with depth that is discernable beyond the resolution of the various thermobarometers. The peridotites can be divided into two compositional zones—a shallow layer dominated by garnet harzburgite that straddles the diamond–graphite boundary and a deeper layer that is strongly dominated by garnet lherzolite. Compositionally, the harzburgites (and to a lesser extent, the shallow lherzolites) are ultra-depleted relative to the more fertile deeper layer, irrespective of whether they reside within the graphite or diamond stability field. This ultra-depleted layer beneath Ekati continues to 150 km.     

Synthesis and properties of ammoniojarosites prepared with iron-oxidizing acidophilic microorganisms at 22-65 °C

Ammoniojarosite [(NH₄,H₃O)Fe₃(OH)₆(SO₄)₂], a poorly soluble basic ferric sulfate, was produced by microbiological oxidation of ferrous sulfate at pH 2.0-3.0 over a range of concentrations (5.4-805 mM) and temperatures (22-65 °C). Ammoniojarosites were also produced by chemical (abiotic) procedures in parallel thermal (36-95 °C) experiments. At 36 °C, schwertmannite [ideally Fe₈O₈(OH)₆(SO₄)] was the only solid product formed at <10 mM concentrations. Between 11.5 and 85.4 mM , a mixed product of ammoniojarosite and schwertmannite precipitated, as identified by X-ray diffraction. In excess of 165 mM , ammoniojarosite was the only solid phase produced. An increase in the incubation temperature using thermoacidophiles at 45 and 65 °C accelerated the formation of ammoniojarosite in culture solutions containing 165 mM . Both the biogenic and chemical ammoniojarosites were yellow (2Y-4Y in Munsell hue), low surface area (<1 m²/g), well crystalline materials with average c_o and a_o unit cell parameters of 17.467 ± 0.048 Å and 7.330 ± 0.006 Å, respectively. Strong positive correlations were observed between unit cell axial ratios (c_o/a_o) and increasing synthesis temperature in both biotic and abiotic systems. All samples were N deficient compared to stoichiometric ammoniojarosite, and both chemical and X-ray data indicated partial replacement of by H₃O⁺ to form solid solutions with 0.14-0.24 mole H₃O⁺ per formula unit. The morphology of the biogenic jarosites included aggregated discs, pseudo-cubic crystals and botryoidal particles, whereas the chemical specimens prepared at 36-95 °C were composed of irregular crystals with angular edges. Morphological information may thus be useful to evaluate environmental parameters and mode of formation. The data may also have application in predicting phase boundary conditions for Fe(III) precipitation in biogeochemical processes and treatment systems involving acid sulfate waters.     

Wave Energy from the North Sea: Experiences from the Lysekil Research Site

This paper provides a status update on the development of the Swedish wave energy research area located close to Lysekil on the Swedish West coast. The Lysekil project is run by the Centre for Renewable Electric Energy Conversion at Uppsala University. The project was started in 2004 and currently has permission to run until the end of 2013. During this time period 10 grid-connected wave energy converters, 30 buoys for studies on environmental impact, and a surveillance tower for monitoring the interaction between waves and converters will be installed and studied. To date the research area holds one complete wave energy converter connected to a measuring station on shore via a sea cable, a Wave Rider? buoy for wave measurements, 25 buoys for studies on environmental impact, and a surveillance tower. The wave energy converter is based on a linear synchronous generator which is placed on the sea bed and driven by a heaving point absorber at the ocean surface. The converter is directly driven, i.e. it has no gearbox or other mechanical or hydraulic conversion system. This results in a simple and robust mechanical system, but also in a somewhat more complicated electrical system.     

Estimating the parameters of forest inventory using machine learning and the reduction of remote sensing features

Locally computed statistics of image texture and a case-based reasoning (CBR) system were evaluated for mapping of forest attributes. Cluster analysis was preferred to regression models, as a pre-selection method of features. The best stand-based accuracy using satellite sensor images was 74.64 m⁻³ ha⁻¹ (36%) RMSE for stand volume, 1.98 m⁻³ ha⁻¹ a⁻¹ (49%) for annual increase in stand volume, where κ = 0.23 for stand growth classes and κ = 0.41 for dominant tree species in stands. The top pixel-based accuracy using orthophotos was 76.54 m⁻³ ha⁻¹ (41%) RMSE for stand volume, 1.87 m⁻³ ha⁻¹ a⁻¹ (44%) for annual increase in stand volume, where κ = 0.24 for stand growth classes and κ = 0.38 for dominant tree species in stands. Mean saturation in 30 m radius was the most useful feature when orthophotos were used, and standard deviation of Landsat ETM 6.2 values in 80 m radius was the best when satellite sensor images were used. The most valuable feature components (radii, channels and local statistics) for orthophotos were: 30 m kernel radius, lightness and the mean of pixel values; for satellite sensor images: 80 m kernel radius, near-infrared channel (ETM 4) and the mean of pixel values. Locally computed statistics.     

Asteroid lightcurve phase shift from rough‐surface shadowing

We have simulated asteroid lightcurves for simple shape models using a realistic surface scattering law. The scattering law includes a shadowing function computed with numerical ray‐tracing. We computed lightcurves in a variety of illumination geometries for both the traditional Lommel–Seeliger law and our seminumerical law. We observe a shift in the rotational phase of the lightcurves, which depends on the parameters of the scattering law as well as the illumination geometry and the direction of the spin axis of the asteroid. This phase shift is always zero at opposition, and can be as large as 10° for illumination geometries typical for Main Belt asteroids. The phase shift has implications on the accuracy of other results which are based on asteroid lightcurve analysis, such as spin‐state or shape determination.     

Development of potential ecological niches in impact-induced hydrothermal systems: The small-to-medium size impacts

Effect of meteorite impact on the biological evolution is usually considered by its catastrophic consequences. However, the impacts can create opportunity for other organisms and the structures themselves can serve as suitable ecological niches (oases) for life. In this contribution we present results of modeling of an impact-induced hydrothermal (IHT) system in a small-to-medium sized impact crater, where the development of zones habitable for primitive hydrothermal thermophilic and hypethermophilic microorganisms was studied. The impact and geothermal modeling was verified against the 4-km diameter Kärdla complex structure, Hiiumaa Island, Estonia. If there is an sufficient amount of water present in the target (e.g., sea cover, groundwater or permafrost resources) then the differential temperature fields created by the impact initiate a hydrothermal circulation system within the crater. The results of transient fluid flow and heat transfer simulations in Kärdla suggest that immediately after impact the temperatures in the central area, which contains the most hydrothermal alteration, were well above the boiling point. However, due to efficient heat loss at the groundwater vaporization front, the vapor-dominated area disappears within a few decades. In the central uplift area, the conditions favorable for thermophilic microorganisms (temperatures <100 °C) were reached in 500–1000 years after the impact. The overall cooling to ambient temperatures in the deeper parts of the central uplift lasted for thousands of years. In the crater depression and rim area the initial temperatures, suggested by the impact modeling, were much lower—from 150 °C to ambient temperatures, except locally in fracture zones and suevite pockets. Our data suggest that in small-to-medium size impact craters with insignificant melting, the suitable conditions for hydrothermal microbial communities are established shortly (tens to few hundreds of years as maximum) after the impact in most parts of the crater. In the central uplift area the microbial colonization is inhibited for about a thousand years. However, this is the area, which afterwards retains the optimum temperatures (45–120 °C) needed for hydrothermal microorganisms for the longest period. Geochemical and mineralogical data suggest, in general, neutral pH 7(±1) fluid of the IHT system, which is, when compared to volcanic hydrotherms, richer in dissolved oxygen and poor in reduced compounds. This suggests the preference for sulfur-reducing microorganisms in the possible impact-induced hydrothermal communities.     

Geochemical evolution of groundwater in the Cambrian–Vendian aquifer system of the Baltic Basin

The shallowly buried marginal part of the Cambrian–Vendian confined aquifer system of the Baltic Basin is characterised by fresh and low δ¹⁸O composition water, whereas the deeply settled parts of the aquifer are characterized by typical Na–Ca–Cl basinal brines. Spatial variation in water geochemistry and stable isotope composition suggests mixing origin of the diluted water of three end-members—glacial melt water of the Weichselian Ice Age (115 000–10 000 BP), Na–Ca–Cl composition basin brine and modern meteoric water. The mixing has occurred in two stages. First, the intrusion and mixing of isotopically depleted glacial waters with basinal brines occurred during the Pleistocene glacial periods when the subglacial melt-water with high hydraulic gradient penetrated into the aquifer. The second stage of mixing takes place nowadays by intrusion of meteoric waters. The freshened water at the northern margin of the basin has acquired a partial equilibrium with the weakly cemented rock matrix of the aquifer.