Review study on near-natural conditions of Central European mountain streams, with particular reference to debris and beaver dams: Results of the “REG meeting” 2000

This paper summarises the results of the “Rhithron Ecology Group” meeting in Essen (March 2000), supplemented by a literature evaluation.An extended view of small mountain streams in Central Europe under “potentially natural conditions” is presented. We focus on the potential impact of natural transverse structures (debris dams and beaver dams) on stream morphology, hydrology, habitat composition and communities. Furthermore, impact of other stream morphological features, which are presently lacking in the Central European landscape, is described.We suggest that Central European mountain streams are characterised by a higher proportion of lentic zones under “potentially natural conditions”. Morphological degradation leads to a loss of lentic zones and to an increase of current velocities and corresponding changes in faunal composition, particularly higher abundance and proportion of rheophilic species and a decrease of species preferring lentic zones. This should be regarded in future stream assessment.     

Zeitliche Beziehung zwischen variskischer Tektonik und initialem Magmatismus in Ostthüringen

Zusammenfassung Die voroberdevonischen Kerngesteine des Bergaer Sattels werden von wenige Meter mächtigen konkordanten und diskordanten Diabas-Gängen durchschlagen. Die diskordanten Gänge liegen ausnahmslos in der achsenflächenparallelen Transversalschieferung (s₁). Die Erklärung dieser Lagerungsform durch eine voroberdevonische Schieferung oder durch die Annahme eines nachsudetischen Intrusionsalters stünde im Widerspruch zu den bisherigen Ansichten. Eine genaue Überprüfung dieser s₁-parallelen Gänge erweist deutlich deren Bindung an die Mittelschenkel der Falten niederer Ordnung. Die aus der Schichtung abweichende Intrusion folgte demnach achsenflächenparallelen Schenkelbrüchen tiefoberdevonisch angelegter Embryonalfalten. Sie werden der reußischen Phase v.Gaertners (1951) zugeschrieben. Diese Bewegung an der Wende Mittel-/Oberdevon wird als intrageosynklinale Vorfaltung der saxothuringischen Zone des variskischen Orogens aufgefaßt.Dieser Beitrag ist das Teilergebnis einer regionalgeologischen Untersuchung, deren Anregung und Betreuung Verf. Herrn Professor Dr. F.Deubel verdankt.     

Sedimentation patterns of diatoms in Lake Holzmaar, Germany - (on the transfer of climate signals to biogenic silica oxygen isotope proxies)

The seasonal sedimentation pattern of diatom valves in Lake Holzmaar was investigated during 1995 by deploying sediment traps at three different lake depths. According to the sedimentation pattern, the major reproduction zone of diatoms was restricted to the upper 6 m of the water body. The population growth started late in April and blooms of Cyclotella cf. comensis Grun., which dominates the plankton diatoms, and Fragilaria crotonensis Kitton were collected in traps during June and September, and July, respectively. During summer, the seasonal sedimentation pattern of each taxon, as collected in the upper traps, was reflected in the concentrations in the lowest trap. However, in May and from September onwards, the community composition in the lowest trap and augmented trapping rates suggest both sediment focusing and resuspension of bottom sediments.The temperature signals as recorded by 18O values of diatom valves should, therefore, reflect integrated temperatures between 0 and 6 m depth. However, temperatures during summer and autumn are expected to be accentuated in the sedimentary record since the isotopic signal is weighted by both the number and the weight-mass of the valves. During summer, the transfer of these signals by the sedimenting diatoms retains the information pattern recorded, while in spring and autumn/winter additional influxes caused by resuspension may somewhat alter those temperature informations. The proxy signals finally stored in the sediments, may, therefore, not precisely represent the successive temperatures currently recorded during 1995 within mid-lake.     

Zum Problem der „Dynamischen Bezugsfläche“, insbesondere im Golfstromgebiet

Zusammenfassung In der Ozeanographie ist cs üblich, als dynamische Bezugsfläche eine Nullfläche zu wählen, d. h. eine Fläche im baroklinen Ozean, in der die Geschwindigkeit der Strömung verschwindet. Die Kenntnis dieser Tiefe, also der Untergrenze des Strömungssystems, ist nicht nur eine Voraussetzung für die Berechnung absoluter Strömungen nach der klassischen Methode, sondern auch wichtig für eine Analyse der Dynamik ozeanischer Zirkulationsvorgänge.Bei der theoretischen Behandlung cines vertikal und horizontal geschichteten Ozeans mit Hilfe der vertikal integrierten Bewegungsgleichungen treten Glieder auf, die eine Kenntnis der Tiefenlage des Strömungssystems voraussetzen. Nur im Falle sehr spezieller Bedingungen oder einer konstanten Tiefe des Zirkulationssystems verschwinden die von der Untergrenze abhängigen Glieder.In der vorliegenden Arbeit wird an einem einfachen Modell der Einfluß einer variablen Tiefe der Untergrenze des Strömungssystems auf den horizontalen Massentransport diskutiert. Ein interessantes Beispiel bietet das Stromsystem an der Ostküste von Nordamerika, wo das Feld des Golfstromes einem äquivalent-barotropen System zuzustreben scheint. Ein solches Feld erfordert einen starken Abfall der Untergrenze der Strömung von der linken zur rechten Flanke, d. h. vom Kontinentalschelf zur Sargassosee. Die so geforderte Nullfläche stimmt gut mit der nach der D efantschen Methode bestimmten überein.

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On the problem of the dynamical reference surface with special consideration of the Gulf Stream

Summary It has become a customary practice in oceanography to choose as a dynamical reference surface a zerolevel, that is, a surface in the barocline ocean where the current velocities vanish. The knowledge of the depth of such a surface, or of the lower boundary of the current system, is not only required for computing absolute currents according to the classical method, but it is also important for an analysis of the dynamics of the oceanic circulation.When dealing theoretically with a stratified ocean by means of the vertically integrated equations of motion, additional terms appear in the basic equations which depend on the depth of the lower boundary of the current system. The terms which depend on the variable depth of this lower boundary would disappear only in the case of very special conditions or of a constant depth of the circulation.The present paper discusses a simple model which shows the effect of a variable depth of the lower boundary of the current system on the horizontal mass transport. An interesting example is offered by the currents off the east coast of North America, where the current field of the Gulf Stream seems to approach an equivalent-barotropic system. Such a field requires a strong slope of the lower boundary of the current, that is, of the zero level, from the left to the right hand border, or from the continental shelf towards the Sargasso Sea. This zero level as requir ed theoretically for stationary currents agrees well with the level of no motion as determined by the method of A. Defant.

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Sur le problème d'une «surface de référence dynamique» discuté en considération spéciale de la région du courant du Golfe

Résumé Les océanographes ont pris l'habitude de choisir comme «surface de référence dynamique» un «niveau de zéro», c. a. d. une surface dans l'océan barocline où la vitesse devient nulle. La connaissance de la situation en profondeur d'une surface, donc, la limite inférieure du système de courants est non seulement indispensable au calcul des courants absolus d'après la méthode classique mais aussi importante à l'analyse de la dynamique de la circulation océanique.Si l'on étudie théoriquement un océan stratifié en se servant des équations de mouvements verticalement intégrées, on rencontre dans les équations fondamentales des termes additionnels qui dépendent de la limite inférieure du système de courants. Ces termes qui dépendent de la profondeur variable de cette limite inférieure disparaîtront seulement en cas de conditions très spéciales ou de présence d'une profondeur constante du système de circulation.Le travail actuel discute à l'aide d'un exemple simple l'influence qu'une profondeur variable de la limite inférieure du système de courants exersc sur le transport horizontal de masse. Le système de courants devant la côte orientale de l'Amérique du Nord où le champ du courant de Golfe semble s'approcher d'un système équivalent-barotrope en offre un exemple intéressant. Un tel champ nécessite une forte inclinaison de la limite inférieure du courant, c. a. d. une inclinaison allant du bord gauche au bord droit du niveau de zéro ou du plateau continental jusqu'à la mer des Sargasses. Ce niveau de zéro, comme il est théoriquement dérivé en cas des courants stationnaires, est en bon accord avec le niveau sans mouvement déterminé d'après la méthode de Defant.

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Herrn Professor Dr. Gerhard Schott zum 90. Geburtstag gewidmet.     

Distribution and activity of petroleum hydrocarbon degrading bacteria in the North Sea and Baltic Sea

Summary Data were collected in 1988 and 1989 on the distribution and activity of petroleum hydrocarbon degrading bacteria in the North Sea and Baltic Sea. Crude oil degrading bacteria and the number of bacteria which in particular degrade naphthalene were quantified using a modified dilution method (MPN). Crude oil degrading bacteria were present in all of about 100 water samples, with as many as 10³ ml^–1 in some samples. Numbers of naphthalene degrading bacteria were at least tenfold lower. There is obviously a greater connection between this bacteria group and petroleum hydrocarbon (PHC) contamination than between the more nonspecific group of crude oil degrading bacteria and PHC contamination. Data from the North Sea show an extremely high abundance of hydrocarbon degrading bacteria, even in winter, while in the southern Baltic Sea low numbers of bacteria were found and slower crude oil degradation was observed.

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Verteilung und Aktivität von erdölkohlenwasserstoffabbauenden Bakterien in Nord- und Ostsee

Zusammenfassung 1988 und 1989 wurden Daten über Verteilung und Aktivität von erdölkohlenwasserstoffabbauenden Bakterien in Nord- und Ostsee gesammelt. Rohölabbauende Bakterien und die Zahl von Bakterien, die insbesondere Naphthalen abbauen, wurden mit einer modifizierten Lösungsmethode (MPN) bestimmt. Rohölabbauende Bakterien wurden in allen ca. 100 Wasserproben nachgewiesen; in einigen Proben mit nicht weniger als 10³/ml. Die Zahl der naphthalenabbauenden Bakterien war mindestens um den Faktor 10 kleiner. Ein stärkerer Zusammenhang zwischen dieser Bakteriengruppe und der Belastung des Meerwassers durch Erdöl-Kohlenwasserstoffe als zwischen der eher unspezifischen Gruppe der rohölabbauenden Bakterien und dieser Belastung ist wahrscheinlich. Daten aus der Nordsee zeigen, selbst im Winter, eine sehr hohe Zahl von kohlenwasserstoffabbauenden Bakterien, während in der südlichen Ostsee eine niedrigere Anzahl von Bakterien bestimmt und ein langsamerer Rohölabbau beobachtet wurde.

     

Coexisting Ca-poor pyroxenes in the Main Zone of the Bushveld Complex

Electron microprobe analyses of Ca-poor pyroxenes in gabbroic rocks of the Main Zone of the Bushveld Complex reveal that inverted pigeonites have lower Mg/Fe ratios than coexisting hypersthenes. Textural relationships, however, indicate that the two Ca-poor pyroxenes did not crystallize simultaneously from the magma. Early pigeonite reacted with the magma to form hypersthene and the difference in the Mg/Fe ratio of these two pyroxenes reflects the difference of this ratio between early pigeonite and the magma at the time of reaction. Some of the grains of early pigeonite, now inverted to hypersthene, evidently escaped this reaction with the magma. Bulk compositions of pyroxenes intermediate between that of pigeonite and hypersthene are postulated on the grounds of varying amounts of exsolved augite in the hypersthene which has originated from pigeonite by reaction with magma.     

Ray parameters of diffracted long period P and S waves and the velocities at the base of the mantle

The derivation of P and S velocities at the core-mantle boundary (CMB) from long-period diffracted waves by the use of the simple ray-theoretical formulav _CMB=r _c /p (v _CMB=velocity at the CMB;r _c =core radius;p=ray parameter) yields apparent velocity values which differ from the true velocities. Using a dominant period of about 20 sec for calculating theoretical seismograms, we found a linear relation between the apparent velocity and the average velocity in a transition zone at the base of the mantle with fixed velocity on top.The ray parameters determined from long-period earthquake data are found to be 4.540±0.035 and 8.427±0.072 sec/deg for P_diff and S_diff, respectively. These values yield apparent velocities of 13.378±0.103 for P and 7.207±0.062 km/sec for S waves. By means of the theoretical relation between apparent and average velocity and under the assumption of linear variation of velocity with depth, one can invert the apparent velocities into true CMB velocities of 13.736±0.170 and 7.320±0.124 km/sec. These results imply positive velocity gradients at the base of the mantle and hence no significant departures from adiabaticity and homogeneity.Contribution No. 211 of the Geophysical Institute, University of Karlsruhe.     

The molasse facies of the Columbian orogen,Canadian Cordillera

The authors present a tentative model for the relationship between deformation, uplift and molasse sedimentation in the Columbian Orogen of the Canadian Cordillera. Data are mainly drawn from the north-central part of the Columbian Orogen. Two distinct deformational episodes are recognized. The first, probably of mid-Jurassic age, was accompanied by regional metamorphism and resulted in southwesterly directed folds and related faults. This episode of crustal shortening appears to have been the precursor of uplift in the western Columbian Orogen (Omineca Crystalline Belt), causing the progradation of a primogenic non-marine molasse over marine shale and flysch. The second deformation, of probable late Cretaceous to Eocene age, caused overprinting of earlier structures by steep faults in the west and led to the growth of the fold-and-thrust belt of the Rocky Mountains. This episode created a morphogenic drainage system with molasse deposition in intramontane fault basins and along both flanks of the Columbian Orogen. Modal analyses from fluviatile sandstones within the primogenic and morphogenic molasse illustrate the progressive stripping of sedimentary and volcanic units along both sides of the orogenic core zone. Post-orogenic drainage from Miocene to Recent was strongly modified by the development of high-gradient drainage towards the Pacific Ocean.     

The role of CO2 in the genesis of olivine melilitite

The nature of the near-liquidus phases for a mantle-derived olivine melilitite composition have been determined at high pressure under dry conditions and with various water contents. Olivine and clinopyroxene occur on or near the liquidus and there are no conditions where orthopyroxene crystallizes in equilibrium with the olivine melilitite. We have determined the effect on the liquidus temperature and liquidus phases of substituting CO₂ for H₂O on a mole for mole basis at 30 kb, using olivine melilitite + 20 wt% H₂O at = 0 and = (CO₂)/(H₂+CO₂) (mole fraction) = 0.25, 0.5, 0.75 and 1.0 (i.e. olivine melilitite + 38 wt% CO₂). Experiments were buffered by the MH or NNO buffers. At 30 kb, CO₂ is only slightly less soluble than water for <0.5 as judged by the slight increase in liquidus temperature on mole-for-mole substitution of CO₂ for H₂O and at 30 kb, 1200° C, = = 0.5 the olivine melilitite contains 8.8 wt% H₂O and 21 wt% CO₂ in solution. For 1 the CO₂ saturated liquidus is depressed 70 ° C below the anhydrous liquidus and the magma dissolves approx. 17% CO₂ at 30kb, 1400 ° C, 1, 0. Infrared spectra of quenched glasses have absorption bands characteristic of CO ₃ ⁼ and OH- molecules and no evidence for HCO ₃ ^- . The effect of CO ₃ ⁼ molecules dissolved in the olivine melilitite at high pressure is to suppress the near-liquidus crystallization of olivine and clinopyroxene and bring orthopyroxene and garnet on to the liquidus. We infer that olivine melilitite magmas may be derived by equilibrium partial melting (<5%) of pyrolite at 30 kb, 1150–1200 ° C, provided that both H₂O and CO₂ are present in the source region in minor amounts. Preferred conditions are 0< <0.5, 0.5< <1, and at low oxygen fugacities (相似文献