Tools and cover effects in bedload transport observations in the Pitzbach,Austria     

Jens M. Turowski  Dieter Rickenmann 《地球表面变化过程与地形》2009,34(1):26-37

We report bedload data and acoustic impulse measurements due to particle impact from the Pitzbach in Austria. Impulse counts can be viewed as a measure of the energy delivered to the bed by moving particles. Impulse counts show a large scatter even for the same discharge and bedload supply. This scatter is due to varying grain size distribution, grain shape, mode of transport of the sediment particles and spatial and temporal distribution of the sediment load. The mean impulse count at given hydraulic conditions may increase or decrease with increasing sediment supply, suggesting that both tools and cover effects are active on the channel bed. Dependent on the local balance between sediment supply and transport capacity, either effect may be dominant at different locations along the cross‐section at the same time. Furthermore, the same bed location may respond to increasing sediment supply as tools‐dominated at some discharges and cover‐dominated at other discharges. Our observations may have implications for modelling of bedrock erosion in landscape evolution models and of bedrock channel morphology. Erosion models that do not incorporate both tools and cover effects are not sufficient to describe observations. Furthermore, a local erosion law cannot in general be used to describe erosion averaged over the channel cross‐section. The changing balance between sediment supply and transport capacity with increasing discharge highlights that a single representative discharge is not sufficient to capture the full erosion dynamics. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Generation and regulation of summer runoff in a boreal flat fen     

Jens Kvrner  Bjrn Klve 《Journal of Hydrology》2008,360(1-4):15-30

Hydrometric measurements, electrical conductivity, water isotopic and hydrochemical components of stream water were used to study summer runoff generation in a flat fen. Different processes generated runoff at low- and high-flows. At storm-flows, fen runoff was generated from overland flow, originating from upland surface water. Temporary storage of water on the fen surface attenuated and delayed flow peaks. At low-flows, runoff at the fen outlet was generated from shallow subsurface flow in the Acrotelm. During low-flow periods, water originated mainly from peat storage water while during episodic events the wetland water storage was renewed by inflowing stream water. Assessment and modeling of hydrological effects of peatlands should be performed separately for low-flows and high-flows, based on the dominating runoff generating processes. Attenuation and retardation of storm-flows in fens by temporary surface storage will depend on the geometric properties of both storage sections and sections controlling outflow. A routing reservoir model adapted for flat fens can be used for simulation of attenuation and retardation in runoff events, and it is suggested that the model concept should be tested for a broader range of peatlands.  相似文献   

Determination of Trace Elements in the Quartz Reference Material UNS-SpS and in Natural Quartz Samples by ICP-MS   总被引：1，自引：0，他引：1  

Thomas Monecke  Gisela Bombach  Werner Klemm  Ulf Kempe  Jens Götze  Dieter Wolf 《Geostandards and Geoanalytical Research》2000,24(1):73-81

A procedure for the digestion and analysis of quartz samples was developed to measure trace element concentrations in natural quartz. The certified glass sand reference material UNS-SpS was chosen to assess the precision, accuracy and detection limit of the analytical method. Quartz was digested with HF/HNO₃ in a closed glassy carbon vessel and analysed by means of quadrupole ICP-MS with external calibration. Analyte concentrations of the sand UNS-SpS were compared with certified and other values from the literature. The abundances of a number of elements (Pr, Gd, Ho and Er) in the reference material are reported here for the first time. The procedure was then applied to three quartz samples from different geological settings to show that trace element data by ICP-MS can distinguish the origin of the sample.  相似文献   

Field instrumentation for high‐resolution parallel monitoring of bedrock erosion and bedload transport          下载免费PDF全文

Alexander R. Beer  Jens M. Turowski  Bruno Fritschi  Dirk H. Rieke‐Zapp 《地球表面变化过程与地形》2015,40(4):530-541

River incision is fundamental in shaping the Earth's surface. In mountainous regions with steep river beds, fluvial bedrock erosion by bedload transport is an important mechanism forming channels. However, there are only a few complete field datasets that can be used to improve process understanding and evaluate erosion models, especially at the process scale. To provide a simultaneous dataset of hydraulics, bedload transport and bedrock erosion at high temporal and spatial resolution, a new measuring device has been installed in the Erlenbach, a gauged stream in the Swiss Pre‐Alps. In this stream, bedload transport rates can be calculated from surveying deposits and from geophone plate sensors and bedload transport samples can be taken directly by an automated moving basket system. To measure bedrock erosion rates simultaneously, two natural stone slabs were mounted flush with the channel bed in a steel frame hosting various measurement devices. Force sensors below the slabs record normal stress and shear stress. At‐a‐point erosion rates on the slab surfaces are continuously measured at sub‐millimetre precision at three locations on each slab. In addition, the slab topography is monitored following erosive flood events. In this article (i) the ‘erosion scale’ device is described, (ii) data resolution and data quality is assessed by means of tests and event data, and (iii) the first transport event is discussed. The erosion scales are confirmed to provide data at high spatio‐temporal resolution for process analysis. The preliminary data show evidence for the tools effect in bedrock erosion. The bedrock slabs can be exchanged to obtain measurements for catchments with different lithologies for comparison. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Climate change impact on North Sea wave conditions: a consistent analysis of ten projections   总被引：1，自引：1，他引：0  

Iris Grabemann  Nikolaus Groll  Jens Möller  Ralf Weisse 《Ocean Dynamics》2015,65(2):255-267

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Estimating tsunami inundation from hurricane storm surge predictions along the U.S. gulf coast   总被引：1，自引：1，他引：0  

Alyssa Pampell-Manis  Juan Horrillo  Jens Figlus 《Ocean Dynamics》2016,66(8):1005-1024

Gulf of Mexico (GOM) coasts have been included in the U.S. Tsunami Warning System since 2005. While the tsunami risk for the GOM is low, tsunamis generated by local submarine landslides pose the greatest potential threat, as evidenced by several large ancient submarine mass failures identified in the northern GOM basin. Given the lack of significant historical tsunami evidence in the GOM, the potential threat of landslide tsunamis in this region is assessed from a worst-case scenario perspective based on a set of events including the large ancient failures and most likely extreme events determined by a probabilistic approach. Since tsunamis are not well-understood along the Gulf Coast, we investigate tsunami inundation referenced to category-specific hurricane storm surge levels, which are relatively well established along the Gulf Coast, in order to provide information for assessing the potential threat of tsunamis which is more understandable and accessible to emergency managers. Based on tsunami inundation studies prepared for the communities of South Padre Island, TX, Galveston, TX, Mobile, AL, Panama City, FL, and Tampa, FL, we identify regional trends of tsunami inundation in terms of modeled storm surge inundation. The general trends indicate that tsunami inundation can well exceed the level of storm surge from major hurricanes in open beachfront and barrier island regions, while more interior areas are less threatened. Such information can be used to better prepare for tsunami events as well as provide a preliminary estimate of tsunami hazard in locations where detailed tsunami inundation studies have not been completed.  相似文献   

Inferring lake depth using diatom assemblages in the shallow,seasonally variable lakes of the Nebraska Sand Hills (USA): calibration,validation, and application of a 69-lake training set     

Avery L. C. Shinneman  Danuta M. Bennett  Sherilyn C. Fritz  Jens Schmieder  Daniel R. Engstrom  Aris Efting  John Holz 《Journal of Paleolimnology》2010,44(2):443-464

The Nebraska Sand Hills are a distinctive eco-region in the semi-arid Great Plains of the western United States. The water table underlying the Sand Hills is part of the High Plains/Ogallala aquifer, an important water resource for the central Great Plains. Lake levels are affected directly by fluctuations in the water table, which is recharged primarily by local precipitation and responds quickly to climatically induced changes in regional water balance. Instrumental records are available for only 50–100 years, and paleolimnological data provide important insights into the extremes and variability in moisture balance over longer time scales. A set of 69 lakes from across Nebraska was used to establish a statistical relationship between diatom community composition and water depth. This relationship was then used to develop a diatom-based inference model for water depth using weighted averaging regression and calibration techniques. Development of the inference model was complicated by strong intra-seasonal variability in water depth and the linkages between depth and other limnologic characteristics, including alkalinity, water clarity and nutrient concentrations. Analysis of historical diatom communities from eight lakes allowed for the reconstruction of lake-level fluctuations over the past several thousand years. Comparisons of the more recent portion of these reconstructions with the instrumental Palmer Drought Severity Index (PDSI) showed that sediment records may not faithfully reflect short-term fluctuations in water level, except where sedimentation rates are very high. However, large and persistent changes in moisture availability were discernible even in longer, low-resolution records. Thus, diatoms are a useful addition to the tools available for understanding past drought in the central Great Plains, especially when trajectories of change are constrained by data from multiple sites or other proxies.  相似文献   

Structure and evolution of the Rockeskyllerkopf Volcanic Complex, West Eifel Volcanic Field, Germany     

Cliff S. J. Shaw  Alan B. Woodland  Jens Hopp  Nesha D. Trenholm 《Bulletin of Volcanology》2010,72(8):971-990

The Rockeskyllerkopf Volcanic Complex (RVC) comprises three overlapping monogenetic volcanic centers: Southeast Lammersdorf (SEL), Mäuseberg (M) and Rockeskyllerkopf (RKK). Each volcanic center comprises proximal wall deposits with a well defined crater wall unconformity and crater fill deposits that partially to completely cover the outer crater wall. The SEL Center is a phreatomagmatic tuff ring composed of lithic rich tephra deposited by pyroclastic falls and surges. The second center, Mäuseberg, with its crater to the northwest of the SEL Center is predominantly magmatic. Topographic and outcrop patterns suggest that this center may have formed a series of overlapping scoria cones along a N–S trending fissure. The youngest center, RKK, which lies on a poorly developed palaeosol within the earlier Mäuseberg deposits, comprises a well developed proximal crater wall sequence. This sequence of magmatic, likely Strombolian, fall and grain avalanche deposits passes upward into a crater fill sequence that comprises variably welded bombs. The final eruptions in the center were massive lava flows that were ponded within the RKK crater. Ar–Ar age dating of reequilibrated fragments of phlogopite megacrysts in the SEL lavas indicates volcanic activity began at 474?±?39 ka. Literature K–Ar dates for the youngest lava flows in the RKK Center give ages of 360?±?60 to 470 ka. Our interpretation of the age data and the presence of the poorly developed palaeosol between the Mäuseberg and RKK centers indicates that volcanism in the RVC began around 470 ka with the eruption of the SEL and Mäuseberg centers followed a few thousand years later by the eruption of the RKK Center.  相似文献   

Depth colonization of eelgrass (<Emphasis Type="Italic">Zostera marina</Emphasis>) and macroalgae as determined by water transparency in Danish coastal waters     

S?ren?Laurentius?NielsenEmail author  Kaj?Sand-Jensen  Jens?Borum  Ole?Geertz-Hansen 《Estuaries and Coasts》2002,25(5):1025-1032

We present a comparative analysis of lower depth limits for growth of eelgrass, large brown algae and other macroalgae measured by SCUBA-diving along 162 transects in 27 Danish fjords and coastal waters, coupled to 1,400 data series of water chemistry (especially nitrogen) and Secchi depth transparency collected between March and October. Danish coastal waters are heavily eutrophied and characterized by high particle concentrations, turbid water and lack of macrophyte growth in deep water. Median values are 3.6 m for Secchi depth and median lower-depth limits are 4.0 m for eelgrass, 5.3 m for brown algae and 5.0 m for other macroalgae. Depth limits for growth of eelgrass and macroalgae increase linearly with transparency in the coastal waters. The relationships are highly significant (p<10⁻⁶) and transparency accounts for about 60% of the variability of depth limits. Eelgrass extends approximately to half the maximum depth of macroalgae, presumably because of greater respiratory costs to maintain the below-ground rhizomes and roots of eelgrass, which often constitutes half the plant weight. As a reflection of the importance of total nitrogen (TN) in controlling phytoplankton biomass and thus Secchi depth in coastal marine waters, we found that TN could explain 48–73% of the variation in depth limits of eelgrass and macroalgae, according to a multiplicative model (Y=aX^b). As with Secchi depth, the relationship to eelgrass showed a lower slope, reflecting the higher respiratory costs of eelgrass. The models show great sensitivity and a profound quantitative response with proportional effects on Secchi depth and depth limits when total-N concentrations are reduced.  相似文献   

B2114+022: a distant radio source gravitationally lensed by a starburst galaxy     

Pedro Augusto †  Ian W. A. Browne  Peter N. Wilkinson  Neal J. Jackson  Chris D. Fassnacht ‡  Tom W. B. Muxlow  Jens Hjorth  reas O. Jaunsen  Leon V. Koopmans  Alok R. Patnaik  Greg B. Taylor 《Monthly notices of the Royal Astronomical Society》2001,326(3):1007-1014

We have discovered a radio source (B2114+022) with a unique structure during the course of the JVAS gravitational lens survey. VLA, MERLIN, VLBA and MERLIN+EVN radio maps reveal four compact components, in a configuration unlike that of any known lens system, or, for that matter, any of the ∼15 000 radio sources in the JVAS and CLASS surveys. Three of the components are within 0.3 arcsec of each other while the fourth is separated from the group by 2.4 arcsec. The widest separation pair of components have similar radio structures and spectra. The other pair also have similar properties. This latter pair have spectra which peak at ∼5 GHz. Their surface brightnesses are much lower than expected for synchrotron self-absorbed components.
Ground-based and Hubble Space Telescope optical observations show two galaxies ( z =0.3157 and 0.5883) separated by 1.25 arcsec. The lower redshift galaxy has a post-starburst spectrum and lies close to, but not coincident with, the compact group of three radio components. No optical or infrared emission is detected from any of the radio components down to I =25 and H =23 . We argue that the most likely explanation of the B2114+022 system is that the post-starburst galaxy, assisted by the second galaxy, lenses a distant radio source producing the two wide-separation images. The other two radio components are then associated with the post-starburst galaxy. The combination of the angular sizes of these components, their radio spectra and their location with respect to their host galaxy still remains puzzling.  相似文献