Responses of Tropical Trees to Rainfall Seasonality and its Long-Term Changes     

Rolf Borchert 《Climatic change》1998,39(2-3):381-393

Seasonality and physiognomy of tropical forests are mainly determined by the amount of annual rainfall and its seasonal distribution. Climatic change scenarios predict that global warming will result in reduced annual rainfall and longer dry seasons for some, but not all, tropical rainforests. Tropical trees can reduce the impact of seasonal drought by adaptive mechanisms such as leaf shedding or stem succulence and by utilization of soil water reserves, which enable the maintenance of an evergreen canopy during periods of low rainfall. Correlations between climate and responses of tropical trees are therefore poor and the responses of tropical rainforests to climatic changes are hard to predict. Predicted climate change is unlikely to affect the physiognomy of rainforests with high annual rainfall and low seasonality. Seasonal evergreen forests which depend on the use of soil water reserves will be replaced by more drought-tolerant semideciduous forests, once rainfall becomes insufficient to replenish soil water reserves regularly. As the limits of drought tolerance of tropical rainforests are not known, rate and extent of future changes cannot be predicted.  相似文献   

The Baltic Sea Experiment BALTEX: A brief overview and some selected results of the authors     

Ehrhard Raschke  Ute Karstens  Ralph Nolte-Holube  Rüdiger Brandt  Hans-Jörg Isemer  Dag Lohmann  Manfred Lobmeyr  Burkhardt Rockel  Rolf Stuhlmann 《Surveys in Geophysics》1998,19(1):1-22

The mechanisms responsible for the transfer of energy and water within the climate system are under worldwide investigation within the framework of the Global Energy and Water Cycle Experiment (GEWEX) to improve the predictability of natural and man-made climate changes at short and long ranges and their impact on water resources. Five continental-scale experiments have been established within GEWEX to enable a more complete coupling between atmospheric and hydrological models. One of them is the Baltic Sea Experiment (BALTEX).In this paper, the goals and structure of BALTEX are outlined. A short overview of measuring and modelling strategies is given. Atmospheric and hydrological model results of the authors only are presented. These include also the validation of precipitation using station measurements as well as validation of modelled cloud cover with cloud estimates from satellite data. Furthermore, results of a large-scale grid based hydrological model to be coupled to atmospheric models are presented.This research has never been possible without the contribution of research groups and operational institutions from all 10 member countries. We concentrate here on results obtained at the GKSS research center.  相似文献   

Transport of Pb and Sr in leaky aquifers of the Bufa del Diente contact metamorphic aureole, north-east Mexico     

Rolf L. Romer  Wilhelm Heinrich 《Contributions to Mineralogy and Petrology》1998,131(2-3):155-170

The Sr and Pb isotopes from the 31.6 ± 0.3 Ma (2σ) old Diente del Bufa alkali syenite, northeastern Mexico, and marbles of its contact aureole were used to trace the sources and the mobility of these metals during hydrothermal activity. Chert layers form aquifers within the marbles. The marbles represent aquitards. During fluid-wallrock reaction, the chert layers developed wollastonite rims. Early wollastonite rims have Sr and Pb isotopic compositions similar to those of their immediate host marbles, which indicates that the isotopic composition of Sr and Pb is initially buffered by the marble. Later wollastonite and other replacement minerals rimming the aquifer have Sr and Pb isotopic compositions that carry with time increasingly larger contributions from the high-salinity magmatic brine. The Sr and Pb contributions from the alkali syenite can be traced isotopically for more than 90 m away from the contact of the intrusion. In contrast, Sr and Pb originating from the alkali syenite are traceable within the marbles only for 3 to 5 cm from the aquifer-marble boundary. This distance is comparable to the spatial distribution of isotopic alterations of C and O implying that Sr and Pb were transported into the marbles through a fluid phase. The isotopic variation of Sr, Pb, C, and O across the aquifer-marble profiles reflects infiltration as a transport mechanism rather than diffusion. Because Sr and Pb are minor components in both the infiltrating fluid and the rock and because their concentrations are strongly affected by the distribution coefficients among the solid phases present, there is little correlation between the isotopic compositions of the trace elements Sr and Pb and those of C and O, which are major components in fluid and rock. Very thin meta-argillite rinds at the outer margin of the aquifer represent residual material after the dissolution of calcite. They are distinctly enriched in Rb, Sr, and U. The Rb and Sr are to some extent residual from the original limestone mineralogy, whereas U is dominantly derived from the magmatic fluid and leaked from the aquifer with the escaping immiscible CO₂-rich H₂O-CO₂ fluid that was produced by decarbonation. The ²³⁸U/²⁰⁴Pb values ranging from 100 to 250 and distinctly lowered Th/U in the meta-argillite rims (1) demonstrate that U was transported with the magmatic fluid along the aquifer and (2) imply that during unmixing of the highly saline magmatic fluid U fractionated into the CO₂-rich H₂O-CO₂ fluid from which it precipitated selectively in the meta-argillite band across the aquifer. Radioautographs demonstrate that the upper meta-argillite rim has 20 to 40 times more U than the lower rim, which implies that 20 to 40 times more CO₂-rich H₂O-CO₂ fluid has left through the upper aquifer contact. Received: 30 September 1997 / Accepted: 15 December 1997  相似文献   

Isotopic composition of Late Mesozoic basic and ultrabasic rocks from the Andes (23–32°S) – implications for the Andean mantle     

Friedrich Lucassen  Monica Escayola  Rolf L. Romer  José Viramonte  Kerstin Koch  Gerhard Franz 《Contributions to Mineralogy and Petrology》2002,143(3):336-349

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Copper and zinc content of periphyton from two rivers as a function of dissolved metal concentration   总被引：5，自引：0，他引：5  

Renata Behra  Rolf Landwehrjohann  Katrin Vogel  Bettina Wagner  Laura Sigg 《Aquatic Sciences - Research Across Boundaries》2002,64(3):300-306

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Lethal and sublethal effects of dredging on reef corals     

Rolf P.M. Bak 《Marine pollution bulletin》1978,9(1):14-16

Effects of dredging on a coral reef are described. Under water light values at a depth of 12–13 m were reduced from about 30% to less than 1% surface illumination. Colonies of coral species which are inefficient sediment rejectors (Porites astreoides) lost their zooxanthellae and died. Calcification rates in Madracis mirabilis and Agaricia agaricites were observed to decrease by 33%. The period of suppressed calcification exceeds that of environmental disturbance.  相似文献   

Zur Petrogenese intermediärer effusiver Magmen     

Prof. Dr. Rolf F. W. Eigenfeld 《International Journal of Earth Sciences》1967,57(1):296-313

Zusammenfassung Die intermediären effusiven Magmen gehen auf ein einziges, auf das olivinbasaltische Magma zurück. Bei dessen langwährendem Eruptionsprozeß aus dem oberen Erdmantel durch die Sialkruste bis zur Oberfläche findet durch Reaktion mit den wall rocks des Grund- und Deckgebirges eine (z.T. selektive) Einschmelzung statt, die zur völligen Syntexis führt. Durch Zunahme von Si, Al und Alkalien aus dem kristallinen Grundgebirge entstehen die übersättigten Vulkanite. Die Desilifizierung der foidführenden Alkaligesteine wird nachDaly undShand durch Assimilation von Kalk, Dolomit und Mergel herbeigeführt.Ungeklärt bleibt hierbei jedoch die Zunahme des Kalis; denn dies war mit seiner Menge dem basischen Ausgangsmagma fremd. An Hand untersuchter Vorkommen in der Rhön und im Kaiserstuhl/Deutschland, im Monzoni-Gebiet/Oberitalien und in der Roccamonfina NW Neapel wird gezeigt, daß es komplexe Vorgänge sind, die die Kali-betonten Alkali-Effusivmagmen schufen. Bereits vor der Syntexis durch Karbonatgesteine waren sie schon einmal gründlich verändert worden durch Assimilation von Alkalisilikatgesteinen des durchbrochenen Grundgebirgssockels.

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The intermediate effusive magmas originate in only one, the olivine basalt magma. During its continuous eruption-process out of the upper mantle through the sial crust to the earth's surface there takes place a (partly selective) assimilation by reaction with the wall rocks of the basement and the sedimentary covering, that leads to a complete syntexis. By increase of silica, alumina and alcalis of the crystalline basement the oversaturated vulcanites are formed. AfterDaly andShand the assimilation of lime, dolomite and marl causes the desilication of the feldspathoid-bearing alcali rocks.Nevertheless the increase of the potassium is indefinite, because it was not in accordance the basic primary magma with regarding its amount. With the aid of investigated rocks of Rhön, Monzoni-district/Upper Italy, Roccamonfina nw. Naples, and Kaiserstuhl there is shown, that complex processes created the potassium-rich alcali-effusive magmas. Already befor syntexis by limestones they were fundamentally transformed by assimilation of alcali-silicate rocks of the broken through basement platform.

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Résumé Les magmas effusives intermédiaires peuvent être ramenés à un seul, le magma olivine-basaltique. Pendant le procès d'éruption lente de celui-ci par l'écorce sialique à la surface il se produit une réaction avec les « wall rocks » du cristallin et du manteau sédimentaire. Cette réaction produit par assimilation des matériaux une syntexis complète. Par augmentation de Si, Al, et des éléments alcalins du socle cristallin se développent les roches volcaniques sursaturées. La désilification des roches alcalines avec feldspathoides se produit d'aprèsDaly etShand par assimilation de calcaires, dolomites et marnes.L'augmentation du potassium reste à expliquer; la grande quantité de potassium n'existe pas dans le magma original basique. Nous avons pu démontrer par la recherche des roches volcaniques de la « Rhön », de « Monzoni » (Italie), de « Roccamonfina » (Naples) et du « Kaiserstuhl » que les réactions, qui produisent les magmas basiques alcalins avec dominance de potassium, sont d'un type très complexe. Ces magmas ont été modifiés à fond avant la syntexis par les roches carbonatiques au cours de l'assimilation des roches alcalo-siliciques du socle cristallin surmonté.

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Iodine Chemistry and its Role in Halogen Activation and Ozone Loss in the Marine Boundary Layer: A Model Study   总被引：6，自引：0，他引：6  

Rainer Vogt  Rolf Sander  Roland von Glasow  Paul J. Crutzen 《Journal of Atmospheric Chemistry》1999,32(3):375-395

A detailed set of reactions treating the gas and aqueous phase chemistry of the most important iodine species in the marine boundary layer (MBL) has been added to a box model which describes Br and Cl chemistry in the MBL. While Br and Cl originate from seasalt, the I compounds are largely derived photochemically from several biogenic alkyl iodides, in particular CH2I2, CH2ClI, C2H5I, C3H7I, or CH3I which are released from the sea. Their photodissociation produces some inorganic iodine gases which can rapidly react in the gas and aqueous phase with other halogen compounds. Scavenging of the iodine species HI, HOI, INO2, and IONO2 by aerosol particles is not a permanent sink as assumed in previous modeling studies. Aqueous-phase chemical reactions can produce the compounds IBr, ICl, and I2, which will be released back into the gas phase due to their low solubility. Our study, although highly theoretical, suggests that almost all particulate iodine is in the chemical form of IO-3. Other aqueous-phase species are only temporary reservoirs and can be re-activated to yield gas phase iodine. Assuming release rates of the organic iodine compounds which yield atmospheric concentrations similar to some measurements, we calculate significant concentrations of reactive halogen gases. The addition of iodine chemistry to our reaction scheme has the effect of accelerating photochemical Br and Cl release from the seasalt. This causes an enhancement in ozone destruction rates in the MBL over that arising from the well established reactions O(1D) + H2O 2OH, HO2 + O3 OH + 2O2, and OH + O3 HO2 + O2. The given reaction scheme accounts for the formation of particulate iodine which is preferably accumulated in the smaller sulfate aerosol particles.  相似文献   

Vyredox — In Situ Purification of Ground Water     

Rolf O Hallberg  Rudolf Martinell 《Ground water》1976,14(2):88-93

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Interaction between meander dynamics and floodplain heterogeneity in a large tropical sand‐bed river: the Rio Beni,Bolivian Amazon          下载免费PDF全文

Arved C. Schwendel  Andrew P. Nicholas  Rolf E. Aalto  Greg H. Sambrook Smith  Simon Buckley 《地球表面变化过程与地形》2015,40(15):2026-2040

The evolution of meandering river floodplains is predominantly controlled by the interplay between overbank sedimentation and channel migration. The resulting spatial heterogeneity in floodplain deposits leads to variability in bank erodibility, which in turn influences channel migration and planform development. Despite the potential significance of these feedbacks, few studies have quantified their impact upon channel evolution and floodplain construction in dynamic settings (e.g. locations characterized by rapid channel migration and high rates of overbank sedimentation). This study employs a combination of field observations, geographic information system (GIS) analysis of satellite imagery and numerical modelling to investigate these issues along a 375 km reach of the Rio Beni in the Bolivian Amazon. Results demonstrate that the occurrence of clay‐rich floodplain deposits promotes a significant reduction in channel migration rates and distinctive styles of channel evolution, including channel straightening and immobilization of bend apices leading to channel narrowing. Clay bodies act as stable locations limiting the propagation of planform disturbances in both upstream and downstream directions, and operate as ‘hinge’ points, around which the channel migrates. Spatial variations in the erodibility of clay‐rich floodplain material also promote large‐scale (10–50 km) differences in channel sinuosity and migration, although these variables are also likely to be influenced by channel gradient and tectonic effects that are difficult to quantify. Numerical model results suggest that spatial heterogeneity in bank erodibility, driven by variable bank composition, may force a substantial (c. 30%) reduction in average channel sinuosity, compared to situations in which bank strength is spatially homogeneous. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献