Das Kuriosum eines scheinbaren “Tidewindes” im Revier Außenelbe

Zusammenfassung Bei einer Auswertung der Windmessungen deutscher Feuerschiffe für die Sturmflut-Periode Mitte Februar 1962 fiel es auf, daß die Differenzen der Windgeschwindigkeit zwischen den Feuerschiffen Elbe 1 und Elbe 2 offenbar einem bestimmten Rhythmus unterlagen. Da der Abstand der meisten Maxima der Winddifferenz (Elbe 1 minus Elbe 2) etwa 12 Std. betrug, tauchte die Vermutung auf, daß dieser Rhythmus gezeitenbedingt war. Die Mittelbildung über 13 nach den Gezeiten geordnete Fälle ergab denn auch den Tidewind in ausgeprägter Form, wobei das relative Windmaximum von Elbe 1 bei Mitte Ebbstromzeit lag^** und der mittlere Schwankungsbetrag (Maximum — Minimum) 3.6 kn betrug. Eine auf die Gezeiten bezogenen Auswertung von Fällen quasikonstanter Windrichtung ergab noch größere Schwankungsbeträge und vor allem eine gegenläufige Schwingung des Tidewindes bei westlichen und östlichen Winden. Da dies Verhalten des Windes — nach Vorzeichen und Betrag — recht genau den differentiellen Schwankungen des Gezeitenstromes bei Elbe 1 und Elbe 2 entsprach, so hätte man an einen Mitführungseffekt des strömenden Wassers auf die Luft denken können, wäre nicht die ungeschwächte Übertragung von Bewegungsgröße bis in Anemometerhöhe von 18 m allzu unwahrscheinlich gewesen. Tatsächlich erlischt, wie E. R. Reiter [1955] zeigen konnte, der Mitführungseffekt bei einem Flusse ähnlicher Geschwindigkeit wie die Außenelbe in etwa 3 m Höhe über Wasser.Des Rätsels Lösung liegt in der kombinierten Wirkung des Gezeitenstroms und des Windes auf die Lage (Kielrichtung) der vor Anker schwojenden Feuerschiffe. Damit verändert sich im Verlauf einer Tide — bei konstanter Windrichtung — die Anblasrichtung der Schiffe, und diese Änderungen des Anströmungswinkels ergeben systematische Änderungen der gemessenen. Windgeschwindigkeit in Abhängigkeit von der Strömmungsstörung am Schiffshindernis. Die mit dem Gezeitenstrom schwojenden Feuerschiffe erscheinen so als ein geeignetes Versuchsobjekt zur besseren Feststellung des quantitativen störenden Schiffseinflusses auf den Wind.

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The strange phenomenon of an apparent tidal wind in the Estuary of the Outer Elbe (Außenelbe)

Summary When the wind measured by the German lightvessels for the storm surge period mid February 1962 was studied, it became obvious that the differences of wind velocities observed on the lightvessels Elbe 1 and Elbe 2 showed a certain rhythm. As most maxima of these wind differences (Elbe 1 minus Elbe 2) followed one another within about 12 hours, it was supposed that this rhythm was connected with the tide. The average of a series of 13 tides showed very remarkably the tidal wind, the maxima of the wind differences being at the centre of the ebbstream interval at Elbe 1 and the mean range of maximum-minimum being 3.6 kn. Cases of wind with quasi-constant directions showed even greater values of deviation when referred to the tide and, above all, deviations in opposite directions at easterly and westerly winds. As this phenomenon, in sign and quantity, very nearly corresponded to the differences of the tidal currents at Elbe 1 and Elbe 2, one could have thought of an effect by which air is carried along by the streaming water, if not, up to the height of the anemometer of 18 m, the unweakened transfer of momentum would have been too unlikely. In fact, as E. R. Reiter [1955] demonstrated, the effect of air being carried along by the streaming water fades out at about 3 m above the water level of a river at similar velocities as the Outer Elbe.The explanation of this phenomenon is the combined effect of the tidal current and the wind on the course of the lightvessels swinging round their anchors. At a constant direction of the wind, during one tide, the angle between wind and course varies and this variation of the angle leads to a systematic variation of the measured wind speed according to the disturbance caused by the ship as an obstacle. Therefore, lightvessels swinging round with the tidal current seem to be a suitable test to study how much the ship herself disturbs the wind.

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Aspect curieux d'un «vent de marée» apparent dans la zone de l'Elbe extérieure

Résumé A l'occasion d'une étude des vitesses du vent mesurées aux bateaux-feu au cours des ondes de tempête de mi-février 1962, on fit la remarque que les différences de vitesse du vent entre les bateaux-feu «Elbe 1» et «Elbe 2» paraissaient obéir à un certain rythme. Comme l'écart de la plupart des maxima de différence («Elbe 1» moins «Elbe 2») était d'environ 12 heures, il vint d'abord à l'esprit, que ce rythme était subordonné à la marée. La moyenne obtenue dans 13 cas pris dans l'ordre suivant la marée, faisait d'ailleurs apparaître nettement le «vent de marée» pour lequel le maximum relatif de «Elbe 1» correspondait au «milieu de la période de jusant» et la variation moyenne (maximum-minimum) se chiffrait à 3.6 noeuds. Une étude, rapportée à la marée, de cas de direction de vent quasi-constante, fit apparaître des variations encore plus grandes et surtout une oscillation en sens contraire du «vent de marée» par vents d'Ouest-d'Est. Comme ce comportement du vent-selon prévision et grandeur correspondait très exactement aux variations différentielles du courant de marée à «Elbe 1» et «Elbe 2», on aurait pu penser à un effet d'entraînement exercé sur l'air par le courant d'eau, si cet entraînement n'avait gardé la même force jusqu'à la hauteur de 18 m de l'anémomètre, ce qui était invraisemblable. En fait, comme l'a montré E. R. Reiter [1955] l'effet d'entraînement pour un fleuve d'une vitesse analogue à l'Elbe extérieure, cesse de se faire sentir à environ 3 m au-dessus de l'eau.Cette énigme trouve son explication dans l'action combinée du courant de marée et du vent sur la situation (direction de la quille) des bateaux-feu évitant sur leur ancre. C'est ainsi qu'au cours d'une marée-le vent gardant la même direction-le navire reçoit le vent sous des angles variables. Il en résulte des modifications systématiques de la vitesse de vent mesurée qui dépend de l'obstacle que le navire présente au courant d'air. Ainsi les bateaux-feu s'évitant au courant de marée semblent fournir un élément d'expérience approprié pour une meilleure détermination quantitative de l'influence perturbatrice du navire sur le vent.

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Herrn Prof. Dr. H. U. Roll zum 60. Geburtstag gewidmet.     

U.S. Mussel Watch: 1977–1978 results on trace metals and radionuclides

The results of the U.S. Mussel Watch Monitoring Program for the period 1976–1978 for trace metals and artificial radionuclides in bivalves are presented. The substances analysed included Ag, Cu, Zn, Cd, Ni, Pb, ²³⁸Pu, ^239+240Pu and ²⁴¹Am. The analyses of organic substances will be presented elsewhere. The concentrations of these substances in the bivalves may reflect upwelling processes, anthropogenic inputs or natural levels. Off the California coast, mussels show markedly elevated Pu and Cd concentrations in coastal areas adjacent to the most intensive upwelling zones. Elevated levels of Pb, for example, are found in organisms living adjacent to highly urbanized places. The general patterns of distribution repeat themselves year after year at a given site. Thus, it is concluded that annual monitoring activities may not be necessary and that a frequency of sampling of several or so years may be more appropriate to identify pollution problems. Finally, national or regional baselines for metal concentrations in bivalves from unpolluted waters are proposed. National baselines for Pb in the west coast mussels of 1·0 parts 10^?6 and for Ag in east coast mussels of 0·05 parts 10^?6 are suggested.     

Anisotropy of magnetic susceptibility variations in a single icelandic columnar basalt

Measurements of the anosotropy of magnetic susceptibility in 34 specimens drilled from a single Icelandic columnar basalt segment reveal a preferred, long-axis alignment of magnetic minerals normal to the long axis of the column and well grouped. Maximum elongation of these minerals occurs in regions which crystallized late, as independently indicated by relative samarium concentrations. We propose that the variations in magnetic mineral elongation are controlled by variations in thermal stress in the cooling column, before complete solidification. An upper limit of 75–100 bars is suggested for these stresses.     

Fish assemblage stability over fifty years in the Lake Pontchartrain estuary; Comparisons among habitats using canonical correspondence analysis

We assessed fish assemblage stability over the last half century in Lake Pontchartrain, an environmentally degraded oligohaline estuary in southeastern Louisiana. Because assemblage instability over time has been consistently associated with severe habitat degradation, we attempted to determine whether fish assemblages in demersal, nearshore, and pelagic habitats exhibited change that was unrelated to natural fluctuations in environmental variables (e.g., assemblage changes between wet and dry periods). Collection data from three gear types (trawl, beach seine, and gill nets) and monthly environmental data (salinity, temperature, and Secchi depth) were compared for four collecting periods: 1954 (dry period), 1978 (wet period), 1996–1998 (wet period), and 1998–2000 (dry period). Canonical correspondence analysis (CCA) revealed that although the three environmental variables were significantly associated with the distribution and abundance patterns of fish assemblages in all habitats (with the exception of Secchi depth for pelagic samples), most fish assemblage change occurred among sampling periods (i.e., along a temporal gradient unrelated to changing environmental variables). Assemblage instability was the most pronounced for fishes collected by trawls from demersal habitats. A marked lack of cyclicity in the trawl data CCA diagram indicated a shift away from a baseline demersal assemblage of 50 yr ago. Centroid positions for the five most collected species indicated that three benthic fishes, Atlantic croaker (Micropogonias undulatus), spot (Leiostomus xanthurus), and hardhead catfish (Arius felis), were more dominant in past demersal assemblages (1954 and 1978). A different situation was shown for planktivorous species collected by trawls with bay anchovy (Anchoa mitchilli) becoming more dominant in recent assemblage and Gulf menhaden (Brevoortia patromus) remaining equally represented in assemblages over time. Changes in fish assemblages from nearshore (beach seine) and pelagic (gill net) habitats were more closely related to environmental fluctuations, though the CCA for beach seine data also indicated a decrease in the dominance ofM. undulatus and an increase in the proportion ofA. mitchilli over time. The reduced assemblage role of benthic fishes and the marked assemblage change indicated by trawl data suggest that over the last half century demersal habitats in Lake Pontchartrain have been impacted more by multiple anthropogenic stressors than nearshore or pelagic habitats.     

Sulfur isotope fractionation during growth of sulfate-reducing bacteria on various carbon sources

Stable sulfur isotope fractionation during microbial sulfate reduction is a potential tool to estimate sulfate reduction rates at field sites. However, little is known about the influence of the utilized carbon source on the magnitude of sulfur isotope fractionation. To investigate this effect, both a pure culture (strain PRTOL1) and enrichment cultures from a petroleum hydrocarbon (PHC)-contaminated aquifer were used and grown in batch cultures on various carbon sources with an initial sulfate concentration of 1 mmol/L. As sole carbon sources the PHC components naphthalene, 1,3,5-trimethylbenzene, and heating oil (enrichment culture) and the organic acids acetate, pyruvate, benzoate, and 3-phenylpropionate (enrichment culture and PRTOL1) were used. Sulfate reduction rates of all cultures ranged from 6 ± 1 nmol cm⁻³ d⁻¹ (enrichment culture grown on 1,3,5-trimethylbenzene) to 280 ± 6 nmol cm⁻³ d⁻¹ (enrichment culture grown on pyruvate). Cell-specific sulfate reduction rates ranged from 1.1 × 10⁻¹⁴ mol cell⁻¹ d⁻¹ (PRTOL1 grown on pyruvate) to 1.5 × 10⁻¹³ mol cell⁻¹ d⁻¹ (PRTOL1 grown on acetate). Sulfur isotope enrichment factors (ε) for the enrichment culture ranged from 16.1‰ (3-phenylpropionate) to 34.5‰ (1,3,5-trimethylbenzene) and for PRTOL1 from 30.0‰ (benzoate) to 36.0‰ (pyruvate). Cultures of PRTOL1 always showed higher ε values than the enrichment culture when grown on the same carbon source due to culture-specific properties. Higher ε values were obtained when the enrichment culture was grown on PHC components than on organic acids. No relationship between ε values and cell-specific sulfate reduction rate existed when all data were combined. When comparing the magnitude of ε values determined in this laboratory study with ε values measured at contaminated and uncontaminated field sites, it becomes evident that a multitude of factors influences ε values at field sites and complicates their interpretation. The results of this study help us assess some of the general parameters that govern the magnitude of ε in sulfate-reducing environments.     

Integrated resource management

Food, energy and mineral resources appeared to be available in limitless quantities. The accelerated growth in global population during recent centuries brought about a new situation. We reached the resource limits of Spaceship Earth. This, along with the dawning awareness of the extent of environmental damage to date, have made it necessary to turn to new attitudes as to the use of renewable and non-renewable resources.IRM (Integrated Resource Management) is proposed as a way to rationally balance the use and conservation of natural resources. A databank based on the Geographic Information System (GIS) concept, bringing together all relevant resources of a nation, is the centerpiece of IRM and will make it possible to establish strategies to optimize the long term use of resources, including all relevant environmental factors.