Experimental investigation of the mechanism of the reaction: 1 tremolite+11 dolomite ⇌ 8 forsterite+13 calcite+9 CO2+1H2O

Stoichiometric mixtures of tremolite and dolomite were heated to 50° C above equilibrium temperatures to form forsterite and calcite. The pressure of the CO₂-H₂O fluid was 5 Kb and \(X_{{\text{CO}}_{\text{2}} }\) varied from 0.1 to 0.6. The extent of the conversion was determined by the amount of CO₂ produced. The resulting mixtures of unreacted tremolite and dolomite and of newly-formed forsterite and calcite were examined with a scanning electron microscope. All tremolite and dolomite grains showed obvious signs of dissolution. At fluid compositions with \(X_{{\text{CO}}_{\text{2}} }\) less than about 0.4, the forsterite and calcite crystals are randomly distributed throughout the charges, indicating that surfaces of the reactants are not a controlling factor with respect to the sites of nucleation of the products. A change is observed when \(X_{{\text{CO}}_{\text{2}} }\) is greater than about 0.4; the forsterite and calcite crystals now nucleate and grow at the surface of the dolomite grains, thus indicating a change in mechanism at medium CO₂ concentrations. As the reaction progresses, the dolomite grains become more and more surrounded by forsterite and calcite, finally forming armoured relics of dolomite. Under experimental conditions this characteristic texture can only be formed if the CO₂-concentration is greater than about 40 mole %. These findings make it possible to estimate the CO₂-concentration from the texture of the dolomite+tremolite+forsterite+calcite assemblage. The results suggest a dissolution-precipitation mechanism for the reaction investigated. In a simplified form it consists of the following 4 steps:

1. Dissolution of the reactants tremolite and dolomite.
2. Diffusion of the dissolved constituents in the fluid.
3. Heterogeneous nucleation of the product minerals.
4. Growth of forsterite and calcite from the fluid.

Two possible explanations are discussed for the development of the amoured texture at \(X_{{\text{CO}}_{\text{2}} }\) above 0.4. The first is based upon the assumption that dolomite has a lower rate of dissolution than tremolite at high \(X_{{\text{CO}}_{\text{2}} }\) values resulting in preferential calcite and forsterite nucleation and growth on the dolomite surface. An alternative explanation is the formation of a raised CO₂ concentration around the dolomite grains at high \(X_{{\text{CO}}_{\text{2}} }\) values, leading to product precipitation on the dolomite crystals.     

Model computations on the effect of rising temperature on soil moisture and water availability in forest ecosystems dominated by scots pine in the boreal zone in Finland

Based on model calculations, the moisture of soil for sites with and without a cover of trees under the current and rising temperature was studied assuming a 5 °C increase in annual mean temperature over a period of 100 years. The calculation for southern Finland (61°N) showed that the soil moisture under elevated temperature could be reduced compared to that under current temperature conditions. This was also true for northern Finland (66°N), but there the reduction in soil moisture was less substantial. In particular, when trees were present, the soil moisture during the growing season was reduced due to enhanced evapotranspiration. In the presence of trees, the moisture content of the surface soil was only half that under the current temperature. In these conditions, reduced accumulation of snow and a thin humus layer allowed the soil to freeze to deep layers, thereby causing further reduction in soil moisture due to poor transfer of water deeper in the soil.     

Ein selbstkompensierender Elektrometerröhrenverstärker zur Registrierung des luftelektrischen Potentialgefälles

Zusammenfassung Es wird ein selbstkompensierender Elektrometerröhrenverstärker zur Registrierung des luftelektrischen Potentialgefälles beschrieben. Das Gerät hat einen hohen, über den ganzen Meßbereich konstanten Eingangswiderstand von 10¹⁴ Ohm und eine lineare Anzeige über einen beliebig wählbaren Meßbereich, z. B. von –200 bis + 300 Volt.

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Summary A self-compensating electrometer-tube amplifier for recording the electric field of the atmosphere is described. The instrument has a high input resistance of 10¹⁴ ohms constant over the whole range and a linear indication covering any range desired, as e. g. from –200 to +300 volts.

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Résumé On décrit un amplificateur autocompensateur à lampe électromètre pour l'enregistrement du champ électrique de l'atmosphère. L'apparen possède une forte résistance d'entrée de 10¹⁴ ohms, constante pour toute l'échelle de mesure, et une indication linéaire valable pour n'importe quelle échelle, par exemple de –200 à +300 volts.

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Mit 2 Textabbildungen     

Dust in turbulent circumstellar discs

The collisional model for turbulent discs (Hämeen-Anttila, 1991) is shown to be equivalent to the model if the same coefficient of viscosity is adopted in both cases and if an unknown numerical coefficient in the former model is chosen appropriately. A combination of both approximations is generalized to include the behaviour of dust in the turbulent disc. If the dust grains are not too large, evolution leads to a stable final state having a non-zero temperature. Physical interpretation of the collisional model leads to a new type of turbulence, in which, if a sufficiently large element of gas is randomly displaced even in a stable disc, the resulting oscillations around the equilibrium position are maintained by the orbital energy. This effect produces an irregular wind of 10 to 100 m s^–1 which is sufficient to prevent the sedimentation of dust grains on the equatorial plane.     

Morphological development of the retention basin “Hartheim”: A case study

Flow in rivers and on floodplains is complex as it is affected by several interconnected factors such as topography, sediment transport and vegetation characteristics. The resulting processes are explained by the measure “Hartheim” planned for retention purposes at the Upper Rhine river. On the basis of existing formulas and instruments it is demonstrated that a good estimation of the development of the measure is possible. The proposed procedure is a useful tool for estimating morphological developments of restored river sections.     

What governs macrophyte species richness in kettle hole types? A case study from Northeast Germany

Kettle holes are small, pond-like, depressional wetlands in young moraine landscapes. They mostly undergo a wet-dry cycle and have a high potential for biological species diversity. However, their biodiversity and habitat function is often greatly impacted by surrounding intensive agricultural land use practices.In this study, we used statistical analysis of a large data set from the federal state of Brandenburg (Northeast Germany) to characterise the macrophyte species richness of kettle holes in an interregional context and to determine the factors that influence macrophyte occurrence. We proposed that (1) specific environmental factors, (2) hydrogeomorphic kettle hole types and (3) the regional topography have a major impact on macrophyte species richness. The evaluation of the data was performed using the General Linear Model (GLM) and Canonical Correspondence Analysis (CCA). Each of the analysed factors addresses different parts of the macrophyte species richness, including the target variables overall species richness, plant life and growth forms as well as Red List species.None of the analysis showed effects of the tested environmental factors on overall macrophytes species richness, but on the richness of plant life and growth forms as well as on Red List species. We identified hydroperiod, depth, shore width, kettle hole area, pH, electric conductivity, carbonate hardness and oxygen as key factors for the prediction of species richness of plant life and growth forms. Furthermore, we demonstrate that hydrogeomorphic kettle hole types account for relevant parts of variation in species richness and are useful interregional and integrative indicators to identify kettle holes with protection priority for macrophytes.     

Palaeolimnology of Lake Sapanca and identification of historic earthquake signals,Northern Anatolian Fault Zone (Turkey)

Lake Sapanca is located on a strand of the Northern Anatolian Fault Zone (NAFZ, Turkey), where a series of strong earthquakes (Ms >6.0) have occurred over the past hundred years. Identifying prehistoric earthquakes in and around Lake Sapanca is key to a better understanding of plate movements along the NAFZ. This study contributes to the development of palaeolimnological tools to identify past earthquakes in Lake Sapanca. To this end several promising proxies were investigated, specifically lithology, magnetic susceptibility, grain size (thin-section and laser analysis), geochemistry, pollen concentration, diatom assemblages, ¹³⁷Cs and ²¹⁰Pb. Sedimentological indicators provided evidence for reworked, turbidite-like or homogeneous facies (event layers) in several short cores (<45 cm). Other indicators of sediment input and the historical chronicles available for the area suggest that three of these event layers likely originated from the AD 1957, 1967 and 1999 earthquakes. Recent changes in sediment deposition and nutrient levels have also been identified, but are probably not related to earthquakes. This study demonstrates that a combination of indicators can be used to recognize earthquake-related event layers in cores that encompass a longer period of time.     

Tourism and landscape in South Tyrol

An increasing number of the people responsible for promoting tourism understand the necessity of landscape conservation and sustainable development. Sustainability and the maintenance of regional identity depend on the kind of tourism that takes account of the landscape and stops short of a blind modification of it, for instance through the installation of inappropriate large-scale tourist infrastructure. Since the 1970s South Tyrol, Italy’s most northern province (Autonome Provinz Bozen/Südtirol; Provincia Autonoma di Bolzano/Alto Adige), has engaged in tourism of outstanding quality, centreed on the existing landscape potential. Until today this has been the basis for successful tourism development. In the meantime however, there have been calls in South Tyrol for a quantitative expansion, founded on the implementation of an artificial touristic infrastructure and products. As is the case in many other alpine regions, this could be detrimental to the quality of the landscape. Supported by tourism research and based on the authors’ own long-standing experience, this article analyzes the development and trends of tourism in South Tyrol from a geographical perspective and takes a critical look at the various planning prospects and the problems which might evolve for the landscape and for tourism marketing.     

The impact of the PBL scheme and the vertical distribution of model layers on simulations of Alpine foehn

Summary This paper investigates the influence of the planetary boundary-layer (PBL) parameterization and the vertical distribution of model layers on simulations of an Alpine foehn case that was observed during the Mesoscale Alpine Programme (MAP) in autumn 1999. The study is based on the PSU/NCAR MM5 modelling system and combines five different PBL schemes with three model layer settings, which mainly differ in the height above ground of the lowest model level (z ₁). Specifically, z ₁ takes values of about 7 m, 22 m and 36 m, and the experiments with z ₁ = 7 m are set up such that the second model level is located at z = 36 m. To assess if the different model setups have a systematic impact on the model performance, the simulation results are compared against wind lidar, radiosonde and surface measurements gathered along the Austrian Wipp Valley. Moreover, the dependence of the simulated wind and temperature fields at a given height (36 m above ground) on z ₁ is examined for several different regions. Our validation results show that at least over the Wipp Valley, the dependence of the model skill on z ₁ tends to be larger and more systematic than the impact of the PBL scheme. The agreement of the simulated wind field with observations tends to benefit from moving the lowest model layer closer to the ground, which appears to be related to the dependence of lee-side flow separation on z ₁. However, the simulated 2 m-temperatures are closest to observations for the intermediate z ₁ of 22 m. This is mainly related to the fact that the simulated low-level temperatures decrease systematically with decreasing z ₁ for all PBL schemes, turning a positive bias at z ₁ = 36 m into a negative bias at z ₁ = 7 m. The systematic z ₁-dependence is also observed for the temperatures at a fixed height of 36 m, indicating a deficiency in the self-consistency of the model results that is not related to a specific PBL formulation. Possible reasons for this deficiency are discussed in the paper. On the other hand, a systematic z ₁-dependence of the 36-m wind speed is encountered only for one out of the five PBL schemes. This turns out to be related to an unrealistic profile of the vertical mixing coefficient. Correspondence: Günther Z?ngl, Meteorologisches Institut der Universitat München, 80333 München, Germany