Modelling the responses of mature forest trees to air pollution     

Heiner Schäfer Dr.  Hartmut Bossel  Holger Krieger  Norbert Trost 《GeoJournal》1988,17(2):279-287

Systems analysis of the responses of forest trees to air pollutants led to mathematical models which represent the essential life processes of mature trees (photosynthesis, respiration, growth etc.) under ‘normal’ conditions and — especially — under pollution strees. Computer simulations using these models have made it possible to test and analyse the consequences of — known or hypothetical — pollution effects. The simulation runs have led to the identification of three distinct behavioural modes (growth, stagnation, breakdown) and corresponding stable and unstable system states. The results have produced new insights and contributed to the understanding of the dieback process of spruce and beech trees. The presentation will concentrate on the most recent and most complex of the hitherto existing models, theBeech model.  相似文献   

Some assessments of the potential 2 × CO2 climatic effects on water balance components in the eastern mediterranean     

M. Segal  P. Alpert  U. Stein  M. Mandel  M. J. Mitchell 《Climatic change》1994,27(4):351-371

General circulation model (GCM) coarse evaluations of the climatological impact in the Eastern Mediterranean due to global doubling of the atmospheric CO₂ concentration were used as input for apreliminary estimation of modifications in local processes affecting the water balance in this region. It is suggested that: (i) in the 2 × CO₂ climate theaverage regional change of precipitation associated with typical mid-winter cyclonic systems is relatively small, however, it is associated with redistribution of the regional rainfall; (ii) in the elevated terrain in the northern part of the region, daytime snowmelt due to warm air advection may be enhanced, as much as 2.8 cm per day; and (iii) transpiration in the coastal area of the Eastern Mediterranean may increase by ~ 13% of its current level in the summer and somewhat more in the winter.  相似文献   

Benthic storms,vortices, and particle dispersion in the deep West European basin     

Holger Klein 《Ocean Dynamics》1987,40(3):87-102

Summary During the NOAMP Experiment (September '83 to May '86), 20 benthic storms with velocities of up to 27 cm/s and a duration of between 3 and 25 days, have been observed in a region centered at 47° 20 N and 20° W. The calculation of streamfunction maps shows clearly, that all storms between September '83 and September '84 occur in connection with deep reaching synoptic vortices. These events are important mechanisms for the dispersion of tracers, which are released at the seabed. They enable the particles to pass the interface between the well-mixed bottom boundary layer and the stratified interior of the deep sea. The eddies, with lifetimes of up to several months, trap the particles and facilitate horizontal and vertical transports within the eddy. Each vortex, by means of its shear, deforms a parcel of contaminated water to thin sheets, respectively to thin filaments with regard to two dimensions. This makes small-scale mixing processes work effectively.

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Tiefseestürme, Wirbel und Teilchenausbreitung in der Tiefsee des Westeuropäischen Beckens

Zusammenfassung Während des NOAMP-Experiments wurden in einem Gebietbei 47° 20 N und 20° W 20 Tiefseestürme mit Geschwindigkeiten bis zu 27 cm/s und einer Dauer zwischen 3 und 25 Tagen gemessen. Stromfunktionskarten zeigen, daß, zumindest im Zeitraum von September '83 bis September '84, die Stürme stets im Zusammenhang mit tiefreichenden synoptischen Wirbeln auftreten. Diese Ereignisse sind von herausragender Bedeutung für die Ausbreitung am Tiefseeboden eingebrachter Stoffe. Sie ermöglichen den Austausch von Wasserkörpern durch die Sprungschicht zwischen der stark durchmischten Bodengrenzschicht und dem geschichteten Inneren der Tiefsee. Die Wirbel, mit Lebenszeiten bis zu mehreren Monaten, können Wasserkörper mit Eigenschaften, die ihn von der umgebenden Wassermasse unterscheiden, einfangen und transportieren sie vertikal und horizontal innerhalb des Wirbels. Jeder Wirbel deformiert solche Wasserkörper zu dünnen Scheiben, bzw. zu dünnen Filamenten im Zweidimensionalen, und schafft somit die notwendige Voraussetzung für das Wirken kleinskaliger Vermischungsprozesse.

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Tempêtes de grands fonds, tourbillons, dispersion de particules dans les eaux profondes du Bassin de l'Europe de l'Ouest

Résumé Durant l'expérience NOAMP (septembre 1983 – Mai 1986), vingt tempêtes de grands fonds avec des vitesses supérieures à 27 cm/s et des durées comprises entre 3 et 25 jours, ont été observées dans un secteur centré sur le point 47° 20 nord et 20° ouest. Le calcul des cartes de courant montre clairement que les tempêtes sous-marines observées entre septembre 1983 et semtembre 1984 sont reliées à des tourbillons synoptiques atteignant de grandes profondeurs. Ces évènements sont des mécanismes importants pour la dispersion d'éléments — traces libérés sur le fond de l'océan. Ils permettent aux particules de franchir l'interface entre la couche limite de fond, homogène, et la partie stratifiée de la mer profonde. Les tourbillons qui ont des durées de vie de plusieurs mois, piègent les particules et facilitent leurs transports horizontaux et verticaux au sein même du tourbillon. Chaque tourbillon du fait du cisaillement, transforme un volume d'eau contaminée en minces couches, ou plutôt en minces filets d'eau, si l'on se place dans les deux dimensions. Cela génère en réalité un processus de mélange à petite échelle.

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Changes in hydraulic conductivity of laboratory sand-clay mixtures caused by a seawater-freshwater interface   总被引：5，自引：0，他引：5  

L.C. Goldenberg  M. Magaritz  A.J. Amiel  S. Mandel 《Journal of Hydrology》1984,70(1-4):329-336

The influence of small amounts of clay minerals on the hydraulic conductivity of sandy aquifer was investigated by laboratory experiments. Admixture of up to 1.5% by weight of clay minerals to sand did not cause any measurable decrease of hydraulic conductivity for seawater. Increasing the clay fraction from 1.5% to 10% decreased hydraulic conductivity by one order of magnitude. Montmorillonite caused the strongest decrease; the effect of kaolinite and illite was only half as large. When seawater was flushed by freshwater, hydraulic conductivity of the montmorillonite-sand mixture decreased drastically. However, flushing with freshwater did not measurably affect the hydraulic conductivity of an illite-sand or kaolinite-sand mixture. The explanation for this behaviour is the capability of various types of clay to adsorb different quantities of water between their platelets which induces a gel-droplet formation process. This is governed by the chemical composition and the ionic strength of the solution.  相似文献   

Tree roots — Methodological review and new development in dating and quantifying erosive processes     

Holger Grtner 《Geomorphology》2007,86(3-4):243-251

Exposed roots have been used in Dendrogeomorphology since the 1960s to determine erosion rates. This was done by using the root axis as the relative position of the former soil layer and then relating this measure to the age of the root in order to quantify the amount of soil erosion over time. Recently, wood anatomical research revealed the possibility of determining the first year of exposure of roots due to specific anatomical changes within the respective annual ring. As a consequence, using exposed roots that are still in contact to the soil surface, it is possible to reconstruct the size and position of the root at the time of exposure. Consequently, a new equation is presented to calculate the thickness of the eroded soil layer allowing a detailed reconstruction of erosion rates. The technique also helps to determine if the root was exposed by erosional processes or just by its ongoing secondary growth without any erosion involved.  相似文献   

Vegetation and climate in the Early‐ and Pleni‐Weichselian in northern Central Europe     

Gerfried Caspers  Holger Freund 《第四纪科学杂志》2001,16(1):31-48

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Trace metal dynamics in the water column and pore waters in a temperate tidal system: response to the fate of algae-derived organic matter     

Nicole Kowalski  Olaf Dellwig  Melanie Beck  Maik Grunwald  Sibylle Fischer  Maike Piepho  Thomas Riedel  Holger Freund  Hans-Jürgen Brumsack  Michael E. Böttcher 《Ocean Dynamics》2009,59(2):333-350

Tidal and seasonal behaviour of the redox-sensitive trace metals Mn, Fe, Mo, U, and V have been investigated in the open-water column and shallow pore waters of the backbarrier tidal flats of the island of Spiekeroog (Southern North Sea) in 2002 and 2007. The purpose was to study the response of trace metal cycles on algae blooms, which are assumed to cause significant changes in the redox state of the entire ecosystem. Trace metal data were complemented by measurements of nutrients and enumeration of algae cells in 2007. Generally, Mn and V show a tidal cyclicity in the water column with maximum values during low tide which is most pronounced in summer due to elevated microbial activity in the sediments. Mo and U behave almost conservatively throughout the year with slightly increasing levels towards high tide. Exceptions are observed for both metals after summer algae blooms. Thus, the seasonal behaviour of the trace metals appear to be significantly influenced by productivity in the water column as the occurrence of algae blooms is associated with an intense release of organic matter (e.g. transparent exopolymer particles, TEP) thereby forming larger organic-rich aggregates. Along with elevated temperatures in summer, the deposition of such aggregates favours microbial activity within the surface sediments and release of DOC, nutrients and trace metals (Mn, Mo and V) during the degradation of the aggregates. Additionally, pronounced reducing conditions lead to the reduction of Mn(IV)-oxides and Fe(III)-(oxihydr)oxides, thereby releasing formerly scavenged compounds as V and phosphate. Therefore, pore-water profiles show significant enrichments in trace metals especially from July to September. Finally, the trace metals are released to the open water column via draining pore waters (esp. Mo, Mn, and V) and/or fixed in the sediment as sulphides (Fe, Mo) and bound to organic matter (U). Non-conservative behaviour of Mo in oxygenated seawater, first observed in the investigation area by Dellwig et al. (Geochim Cosmochim Acta 71:2745–2761, 2007a), was shown to be a recurrent phenomenon which is closely coupled to bacterial activity after the breakdown of algae blooms. In addition to the postulated fixation of Mo in oxygen-depleted micro-zones of the aggregates or by freshly formed organic matter, a direct removal of Mo from the water column by reduced sediment surfaces may also play an important role.  相似文献   

Mediterranean quaternary river environments. John Lewin,Mark G. Macklin,and Jamie C. Woodward (Editors), 1995, A. A. Balkema,Rotterdam, vii + 292 pp., $135.00 (hardbound)     

Rolfe D. Mandel 《Geoarchaeology》1996,11(5):437-440

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Seismo-engineering parameters for sites of interim storages for spent nuclear fuel at German nuclear power plants     

Günter Leydecker  Timo Schmitt  Holger Busche  Thomas Schaefer 《Soil Dynamics and Earthquake Engineering》2008,28(9):754-762

Within the scope of the licensing procedure for 12 interim storage facilities for spent nuclear fuel at nuclear power plants (NPP) and one for the dismantling of a NPP in Germany, site-specific expert reports were carried out to determine seismo-engineering design parameters. Our work was based on the German nuclear safety standard KTA 2201 part 1 “Design of Nuclear Power Plants against Seismic Events” which requires the derivation of the design earthquake in terms of (macroseismic) intensity. The intensity of the particular design earthquake was evaluated by the deterministic method stipulated in KTA 2201 part 1. According to the current state-of-the-art of science and technology supplementary to the deterministic approach, probabilistic evaluations were done setting a probability of exceedance for the occurrence of the design earthquake of 10⁻⁵ year⁻¹. Geological development and neotectonic conditions of the site surrounding areas were included in the evaluations. For 13 interim storage facility sites, soil-dependent design spectra and corresponding strong-motion duration values were determined.For sites with low seismic hazard site-specific design spectra from the literature were used. In the case of sites with higher seismic hazard (design earthquakeVII 1/2 MSK) strong-motion registrations representative for the site were selected from world wide data and subsequently evaluated to derive site-specific design spectra.  相似文献   

Anthropocene flooding: Challenges for science and society     

Saman Razavi  Patricia Gober  Holger R. Maier  Roy Brouwer  Howard Wheater 《水文研究》2020,34(8):1996-2000

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