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21.
Stefan Jansen Eva Walpersdorf Ursula Werner Markus Billerbeck Michael E Böttcher Dirk de Beer 《Ocean Dynamics》2009,59(2):317-332
In this article, we describe the dynamics of pH, O2 and H2S in the top 5–10 cm of an intertidal flat consisting of permeable sand. These dynamics were measured at the low water line
and higher up the flat and during several seasons. Together with pore water nutrient data, the dynamics confirm that two types
of transport act as driving forces for the cycling of elements (Billerbeck et al. 2006b): Fast surface dynamics of pore water chemistry occur only during inundation. Thus, they must be driven by hydraulics (tidal
and wave action) and are highly dependent on weather conditions. This was demonstrated clearly by quick variation in oxygen
penetration depth: Seeps are active at low tide only, indicating that the pore water flow in them is driven by a pressure
head developing at low tide. The seeps are fed by slow transport of pore water over long distances in the deeper sediment.
In the seeps, high concentrations of degradation products such as nutrients and sulphide were found, showing them to be the
outlets of deep-seated degradation processes. The degradation products appear toxic for bioturbating/bioirrigating organisms,
as a consequence of which, these were absent in the wider seep areas. These two mechanisms driving advection determine oxygen
dynamics in these flats, whereas bioirrigation plays a minor role. The deep circulation causes a characteristic distribution
of strongly reduced pore water near the low water line and rather more oxidised sediments in the centre of the flats. The
two combined transport phenomena determine the fluxes of solutes and gases from the sediment to the surface water and in this
way create specific niches for various types of microorganisms. 相似文献
22.
Dr. Ursula Röhl 《International Journal of Earth Sciences》1990,79(1):13-26
The interpretation of microfacial and geochemical sediment features resulted in a detailed sequence analysis of Upper Muschelkalk strata in the northern and middle parts of West-Germany. It is now possible to correlate columnar sections at far distances. The method allows to make a synthesis of basin evolution. In this way it also succeed to reconstruct the dynamic activities in an epicontinental sedimentation area. The Upper Muschelkalk strata shows a hierarchically nested development of stratification cycles. There are minor cycles of probably paleotectonic origin, which are only locally significant. The major cycles are basing probably on sea level changes and allow supraregional parallelizations of sections. Indicators of the sea level maximums are clay horizons. They are called »Tonhorizonte« in Southern Germany and could be proved also in the Upper Muschelkalk strata of Northern Germany. So the stratigraphic correlation of the two sedimentation areas, which were so different in paleotectonic views, is possible. 相似文献
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24.
Heinz Sulser Diego García-Ramos Peter Kürsteiner Ursula Menkveld-Gfeller 《Swiss Journal of Geoscience》2010,103(2):257-272
Terebratuloid and cancellothyridoid brachiopods from the South-Helvetic Lutetian (Eocene) of the Fäneren region (NE Switzerland) are described: Carneithyris subregularis (Quenstedt) and two forms of Terebratulina s.l. under open nomenclature. Several species of Alpine and non-Alpine origin, related to Carneithyris subregularis, like Terebratula kickxi Galeotti, Terebratula aequivalvis Schafhäutl and Terebratula hilarionis Davidson show characters, which compare well with Carneithyris subregularis. Two of them, T. aequivalvis and T. hilarionis, are assigned to the genus Carneithyris. The stratigraphy and lithology of the sediments in the study area are reassessed. Life habits and palaeoecology of the brachiopods are discussed. C. subregularis apparently was a free living brachiopod without attachment to the substrate, as indicated by massive accumulations of callosities in the posterior parts of the shell. The variability of the cardinal process, as seen in the studied Carneithyris group can be interpreted as a morphological element to enlarge the surface of attachment of strong diductor muscles in relation to the internal thickening of the individual. 相似文献
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Ecological classification of macrophytes and phytobenthos for rivers in Germany according to the water framework directive 总被引:9,自引:0,他引:9
Jochen Schaumburg Christine Schranz Julia Foerster Antje Gutowski Gabriele Hofmann Petra Meilinger Susanne Schneider Ursula Schmedtje 《Limnologica》2004,34(4):283-301
A new assessment system for macrophytes and phytobenthos in German rivers meeting the requirements of the Water Framework Directive (WFD) of the European Community is described. Biocoenotic types based on biological, chemical and hydromorphological data from over 200 river sites covering the main ecoregions, hydromorphological stream types and degradation forms have been defined. For developing a classification system the quality element macrophytes and phytobenthos was divided into three components: macrophytes, benthic diatoms and remaining phytobenthos. For macrophytes seven types including one subtype, for benthic diatoms 14 types including three subtypes and for the remaining phytobenthos five river types were identified. The benthic vegetation at reference condition was described for most of the river types. Degradation is characterised as deviation in benthic vegetation species composition and abundance from the reference biocoenosis. For classification in five ecological status classes, several metrics were developed and used in combination with existing indices. For some of the described river types additional investigations are necessary before a classification system can be developed. 相似文献
28.
Gregory G. Lemaire Ursula S. McKnight Hanna Schulz Sandra Roost Poul L. Bjerg 《Ground Water Monitoring & Remediation》2020,40(2):40-51
Xenobiotic organic compounds can be discharged from contaminated groundwater inflow and may seep into streams from multiple pathways with very different dynamics, some not fully understood. In this study, we investigated the spatio-temporal variation of chlorinated ethenes discharging from a former industrial site (with two main contaminant sources, A and B) into a stream system in a heterogeneous clay till setting in eastern Denmark. The investigated reach and near-stream surroundings are representative of peri-urban settings, with a mix of high channel alteration and more natural stream environment. We therefore propose an approach for risk assessing impacts arising from such complex contamination patterns, accounting for potential spatio-temporal fluctuations and presence of multiple pathways. Our study revealed substantial variations in pathway contributions and overall contaminant mass discharge to the stream. Variable contaminant contributions arising from both groundwater seepage and urban drains were identified in the channelized part of the north stream, primarily from source A. Furthermore, variations in the hyporheic and shallow groundwater flows were found to enhance contaminant transport from source B. These processes result in an increase of the overall mass of contaminant discharged, correlating with the channels' flow. Thus, an in-stream control plane approach was found to be an effective method for integrating multiple and variable discharge contributions quantitatively, although information on specific contaminant sources is lost. This study highlights the complexity and variability of contaminant fluxes occurring at the interface between groundwater and peri-urban streams, and calls for the consideration of these variations when designing monitoring programs and remedial actions for contaminated sites with the potential to impact streams. 相似文献
29.
Abstract— A meteoritic origin was proposed for the New Quebec Crater in 1949 on the basis of an aerial photograph showing its unique circularity and raised rim amid Precambrian gneisses of the Canadian Shield. At that time, only those few craters associated with meteorites were generally accepted as of impact origin. When the earliest field expeditions failed to find meteorites or impact products, two leading meteoriticists, Frederick C. Leonard and Lincoln LaPaz, cited the “Chubb” Crater as a flagrant example for which claims of meteoritic origin were advanced without valid proof. They also listed the Lake Bosumtwi Crater in Ashanti (now Ghana) among crater-like features, clearly of non-meteoritic origin, misidentified as meteorite craters. Controversy over the origin these two craters continued for decades. In Part I of this paper, we trace the investigations that led to the current acceptance of New Quebec as an authentic impact crater. We note that, for reasons that are not entirely clear, a meteoritic origin for the New Quebec Crater achieved wider acceptance at an earlier date than for the Lake Bosumtwi Crater, where petrographic and chemical evidence is more abundant and compelling. In Part II, we describe the petrography of two impact melt samples from the New Quebec Crater and present new evidence on the degrees of shock metamorphism affecting the accessory minerals: apatite, sphene, magnetite and zircon. Zircon, in particular, shows a range from euhedral grains with no signs of alteration to those decomposed to baddeleyite plus silica. 相似文献
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