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   

Chute channel dynamics in large,sand‐bed meandering rivers     

Michael Grenfell  Rolf Aalto  Andrew Nicholas 《地球表面变化过程与地形》2012,37(3):315-331

Meander bends of many large, sand‐bed meandering rivers are partitioned by chute channels that convey permanent flow, and co‐exist with the mainstem for decades. As a first step toward understanding the dynamics and morphodynamic implications of these ‘bifurcate meander bends’, this study applied binary logistic regression analysis to determine whether it is possible to predict chute initiation based on attributes of meander bend character and dynamics. Regression models developed for the Strickland River, Papua New Guinea, the lower Paraguay River, Paraguay/Argentina, and the Beni River, Bolivia, revealed that the probability of chute initiation at a meander bend is a function of the bend extension rate (the rate at which a bend elongates in a direction perpendicular to the valley axis trend). Image analyses of all rivers and field observations from the Strickland suggest that the majority of chute channels form during scroll–slough development. Rapid extension is shown to favour chute initiation by breaking the continuity of point bar deposition and vegetation encroachment at the inner bank, resulting in widely‐spaced scrolls with intervening sloughs that are positively aligned with primary over‐bar flow. The rivers plot in order of increasing chute activity on an empirical meandering‐braided pattern continuum defined by potential specific stream power (ω_pv) and bedload calibre (D₅₀). Increasing stream power is considered to result in higher bend extension rates, with implications for chute initiation. In addition, chute stability is shown to depend on river sediment load relative to flow discharge (Qs/Q), such that while the Beni may plot in the region of highly braided rivers by virtue of a high potential specific stream power, the formation of stable chute channels is suppressed by the high sediment load. This tendency is consistent with previous experimental studies, and results in a planform that is transitional between single‐thread meandering and braided. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Photodegradation,Photocatalytic, and Aerobic Biodegradation of Sulfisomidine and Identification of Transformation Products by LC–UV‐MS/MS     

Faten Sleman  Waleed M. M. Mahmoud  Rolf Schubert  Klaus Kümmerer 《洁净——土壤、空气、水》2012,40(11):1244-1249

Much attention has recently been devoted to the fate and effects of pharmaceuticals in the water cycle. Removal of antibiotics in effluents by photo‐treatment or biodegradation is a topic currently under discussion. Degradation and removal efficiencies of sulfisomidine (SUI) by photodegradation and aerobic biodegradability were studied. SUI behavior was monitored during photolysis and photocatalysis (catalyst titanium dioxide) using 150‐W medium‐pressure Hg lamp. Also an aerobic bacterial degradation test from the OECD series (closed bottle test (CBT, OECD 301 D)) was performed. The primary elimination of SUI was monitored. Structures of photo‐degradation products were assessed by chromatographic separation on a C18 column with ultraviolet detection at 270 nm and ion trap MS. The results demonstrate that SUI is not readily biodegradable in CBT. Photo catalysis was more is effective than photolysis. SUI underwent photodegradation and several SUI photoproducts were identified. Accordingly, the photodegradation pathway of SUI was postulated. When reaching the aquatic environment, SUI and its photo products can constitute a risk to the environment.  相似文献   

The role of soil moisture initialization in subseasonal and seasonal streamflow prediction – A case study in Sri Lanka     

Sarith P.P. Mahanama  Randal D. Koster  Rolf H. Reichle  Lareef Zubair 《Advances in water resources》2008

The two main contributors to streamflow predictability at subseasonal to seasonal timescales in tropical regions are: (i) the predictability of meteorologic (particularly precipitation) anomalies, and (ii) the land surface soil moisture state at the start of the forecast period. Meteorological predictions at subseasonal timescale are usually fraught with error and may not be dependable. The accurate initialization of soil moisture, as obtained through real-time land data analysis, may provide skill in subseasonal to seasonal streamflow prediction, even when the prediction skill for rainfall is small.  相似文献   

Comparison of Earth’s magnetospheric magnetic field models in the context of cosmic ray physics   总被引：1，自引：0，他引：1  

Laurent Desorgher  Karel Kudela  Erwin O. Flückiger  Rolf Bütikofer  Marisa Storini  Vladimir Kalegaev 《Acta Geophysica》2009,57(1):75-87

Over the last two decades, models of the Earth’s magnetospheric magnetic field have been continuously improved to describe more precisely the different magnetospheric current systems (magnetopause current, symmetric and partial ring currents, tail currents and field aligned currents). In this paper we compare the different Tsyganenko models and the Alexeev and Feldstein model in the context of cosmic ray physics. We compare the vertical cutoff rigidity and asymptotic direction of vertical incidence obtained with these models for the January 20, 2005, ground level enhancement and for the big magnetic storm of April 6, 2000. For the event of January 20, 2005, we study the impact of the differences in asymptotic direction obtained with the models on the radiation dose computation at aircraft altitude. For the magnetic storm of April 6, 2000, we discuss the importance of the different magnetospheric current systems in causing cutoff rigidity variations. Finally we summarise the advantages and drawbacks of the different models in the context of space weather.  相似文献   

Determination of the freshwater budget of tidal flats from measurements near a tidal inlet     

Reiner Onken  Rolf Riethmüller 《Continental Shelf Research》2010

The freshwater budget of a tidal flat area is evaluated from long-term hydrographic time series from an observation pole positioned in a tidal channel in the Hörnum Basin (Germany). For each tidal cycle, the freshwater budget is calculated from the total imported and exported water volumes and the corresponding mean densities. The variability of the budget on a tidal scale is characterised by a period of twice the tidal period, exhibiting a minimum when the tidal flats are dry around daylight hours during the foregoing low tide, and a maximum when low tide occurs at night; enhanced evaporation on the flats at daylight hours is identified as the driving process. On the average over one year, while winter observations are missing, the freshwater budget is negative for the years 2002–2005 and positive only for 2006. The interannual mean is negative and amounts to a freshwater loss of about 2 mm day⁻¹, although the large-scale climate in this region is humid. The results demonstrate that the bulk parametrisations for the latent and sensible heat flux between the ocean and the atmosphere must not be applied for the tidelands.  相似文献