Rill development and soil erosion: a laboratory study of slope and rainfall intensity   总被引：7，自引：0，他引：7  

Catherine Berger  Marcel Schulze  Dirk Rieke‐Zapp  Fritz Schlunegger 《地球表面变化过程与地形》2010,35(12):1456-1467

A total of 15 rainfall simulation experiments were conducted in a 1 m by 2 m box varying slope (10, 20, 30%) and rainfall intensity (60, 90, 120 mm h^?1). The experiments were performed to study how rill networks initiate and evolve over time under controlled conditions with regard to the treatment variables considered, and to allow for input in a computer simulation model. Runoff and sediment yield samples were collected. Digital elevation models were calculated by means of photogrammetry for several time steps of most experiments. The soil used in the experiments was a basal till derived Cambisol typical for the Swiss Plateau. While significant differences were found for sediment yield, runoff did not vary significantly with treatment combinations. Increasing rainfall intensity had a larger effect on sediment yield than increasing slope. Rill density and energy expenditure decreased with time, suggesting that energy expenditure was a useful parameter to describe the emergence of rill network at the laboratory scale. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Morphometric techniques allow environmental reconstructions from low-diversity continental ostracode assemblages     

Thijs Van der Meeren  Dirk Verschuren  Emi Ito  Koen Martens 《Journal of Paleolimnology》2010,44(4):903-911

Quantification of intra-specific morphological variability of aquatic biota along environmental gradients can produce biological proxies that can be applied to paleoenvironmental reconstructions. This morphology-derived proxy information can be especially valuable when dealing with low-diversity fossil assemblages, i.e. in situations when paleoenvironmental inference based on species composition of the assemblage is less effective. We analyzed valve size and outline shape of the widespread and highly environmentally tolerant ostracode species Limnocythere inopinata collected in 15 lakes and ponds of Western Mongolia. We quantified shape variability among and within these living populations in relation to water chemistry and physical habitat variables. Our results indicate that: (1) a population’s mean valve outline is related to habitat type, (2) surface water temperature, the alkalinity to sulphate ratio, specific conductance and total phosphorus together explain a high portion of the variance in mean valve outline between populations, and (3) a quantitative model inferring the alkalinity to sulphate ratio from mean valve outline has an R2 of 0.88 and RMSEP of 0.17. These results corroborate the hypothesis that high morphological variability in this ostracode species is due to both ecophenotypic variance and high clonal diversity associated with a mixed reproductive strategy (a combination of sexual and parthenogenetically reproducing lineages), and underline the value of morphometric techniques in paleoecology.  相似文献   

Towards radiocarbon calibration beyond 28 ka using speleothems from the Bahamas     

Dirk L. Hoffmann  J. Warren Beck  David A. Richards  Peter L. Smart  Joy S. Singarayer  Tricia Ketchmark  Chris J. Hawkesworth 《Earth and Planetary Science Letters》2010,289(1-2):1-10

We present a new speleothem record of atmospheric Δ¹⁴C between 28 and 44 ka that offers considerable promise for resolving some of the uncertainty associated with existing radiocarbon calibration curves for this time period. The record is based on a comprehensive suite of AMS ¹⁴C ages, using new low-blank protocols, and U–Th ages using high precision MC-ICPMS procedures. Atmospheric Δ¹⁴C was calculated by correcting ¹⁴C ages with a constant dead carbon fraction (DCF) of 22.7 ± 5.9%, based on a comparison of stalagmite ¹⁴C ages with the IntCal04 (Reimer et al., 2004) calibration curve between 15 and 11 ka. The new Δ¹⁴C speleothem record shows similar structure and amplitude to that derived from Cariaco Basin foraminifera (Hughen et al., 2004, 2006), and the match is further improved if the latter is tied to the most recent Greenland ice core chronology (Svensson et al., 2008). These data are however in conflict with a previously published ¹⁴C data set for a stalagmite record from the Bahamas — GB-89-24-1 (Beck et al., 2001), which likely suffered from ¹⁴C analytical blank subtraction issues in the older part of the record. The new Bahamas speleothem ?¹⁴C data do not show the extreme shifts between 44 and 40 ka reported in the previous study (Beck et al., 2001). Causes for the observed structure in derived atmospheric Δ¹⁴C variation based on the new speleothem data are investigated with a suite of simulations using an earth system model of intermediate complexity. Data-model comparison indicates that major fluctuations in atmospheric ?¹⁴C during marine isotope stage 3 is primarily a function of changes in geomagnetic field intensity, although ocean–atmosphere system reorganisation also played a supporting role.  相似文献   

Noise levels of superconducting gravimeters at seismic frequencies   总被引：6，自引：0，他引：6  

Dirk Banka  & David Crossley 《Geophysical Journal International》1999,139(1):87-97

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Image‐ray Tomography     

Dirk Gajewski  Martin Tygel 《Geophysical Prospecting》2014,62(3):413-426

Seismic tomography is a well‐established approach to invert smooth macro‐velocity models from kinematic parameters, such as traveltimes and their derivatives, which can be directly estimated from data. Tomographic methods differ more with respect to data domains than in the specifications of inverse‐problem solving schemes. Typical examples are stereotomography, which is applied to prestack data and Normal‐Incidence‐Point‐wave tomography, which is applied to common midpoint stacked data. One of the main challenges within the tomographic approach is the reliable estimation of the kinematic attributes from the data that are used in the inversion process. Estimations in the prestack domain (weak and noisy signals), as well as in the post‐stack domain (occurrence of triplications and diffractions leading to numerous conflicting dip situations) may lead to parameter inaccuracies that will adversely impact the resulting velocity models. To overcome the above limitations, a new tomographic procedure applied in the time‐migrated domain is proposed. We call this method Image‐Incident‐Point‐wave tomography. The new scheme can be seen as an alternative to Normal‐Incidence‐Point‐wave tomography. The latter method is based on traveltime attributes associated with normal rays, whereas the Image‐Incidence‐Point‐wave technique is based on the corresponding quantities for the image rays. Compared to Normal‐Incidence‐Point‐wave tomography the proposed method eases the selection of the tomography attributes, which is shown by synthetic and field data examples. Moreover, the method provides a direct way to convert time‐migration velocities into depth‐migration velocities without the need of any Dix‐style inversion.  相似文献   

Freeze coring soft sediments in tropical lakes     

Dirk Veerschuren 《Journal of Paleolimnology》2000,24(3):361-365

A new freeze corer is described that is specifically designed for operation in warm tropical lakes. It combines the standard wedge-shaped freeze-on container with a 20-liter thermos from which pellets of solid CO₂ descend into the wedge to replace those that have sublimated. This extends the duration of effective freezing from ~20 to ~45 min, sufficient to form an adequate thickness of frozen crust in warm (> 22 °C) lakes and prevent its premature melting during retrieval through the water column. The instrument contains no electrical components, which simplifies construction, operation, and maintenance. The front and back surfaces of the freeze wedge are fitted length-wise with serrated ridges to facilitate removal of the crust as four rectangular sediment slabs. The feasibility of freeze coring studies in tropical regions is mainly determined by the local availability of a large-volume dry ice producer.  相似文献   

Requirements for the Catchment,Treatment, and Surveillance of Drinking Water To Avoid the Transmittance of Pathogenic Bacterial,Viral, and Parasitic Organisms     

Dirk Schoenen 《洁净——土壤、空气、水》2001,29(4):187-196

Measures devised for guaranteeing the supply of epidemiologically and hygienically sound drinking water are generally based on observations made during epidemics and the follow‐up scientific studies. Despite the high level standards that have been attained in the treatment of drinking water, the drinking water‐derived outbreaks still keep cropping up even in the industrialized countries. The outbreaks of the parasites Giardia lamblia and Cryptosporidium parvum, and the recent outbreak in Canada caused by Toxoplasma gondii, again focused our attention to the possible infection risk posed by pathogens in drinking water. The circumstances of the cryptosporidia outbreak in Milwaukee in 1993 can be considered as typical for such outbreaks in which parasites have caused human disease. There are generally two ways of avoiding the transmittance of pathogens by drinking water: (i) use of uncontaminated groundwater, or (ii) treatment of the potentially contaminated one. All surface waters have to be considered potentially contaminated, while the purity of the groundwater depends on the local conditions. Routine disinfection of drinking water should be used to minimize the residual risk posed by pathogens. For purification of fecally contaminated water it is utterly inadequate. Testing of water for pathogens followed by more extensive decontamination measures in the case of positive findings appears to be of little value.  相似文献   

Biological Test for the Detection of Low Concentrations of Infectious Cryptosporidium parvum Oocysts in Water     

Panagiotis Karanis  Dirk Schoenen 《洁净——土壤、空气、水》2001,29(4):242-245

An in vivo SCID mouse infectivity assay was used to determine its capacity to detect the infectivity of low concentrations of Cryptosporidium parvum oocysts in water. This biological test can be applied to demonstrate oocysts infectivity in water samples derived from drinking water supply and/or environmental sources.  相似文献   

A Triggered Depth‐Dependent Sampling System to Overcome the Carry‐Over Effects of the Membrane Interface Probe          下载免费PDF全文

Jan Bumberger  Kilian Peisker  Nils Reiche  Dirk Radny  Peter Dietrich 《Ground Water Monitoring & Remediation》2016,36(3):54-61

The membrane interface probe (MIP) is widely used for the in situ characterization of volatile organic compounds (VOCs) in the subsurface. A main problem using the MIP system is the carry‐over effect of VOCs during the transport from the point of measurement to the detector using a conventional transfer line. This effect results in compound specific retention times, which is shown in disproportionately high measuring signals after the actual penetration of contaminated zones. In consequence, the lower extent of contamination is not clearly identifiable and may be overestimated. The presented field study presents an evaluation of different methods to overcome the carry‐over effect, especially with regard to the required measurement times that are needed to wait for a complete disappearance of the detector signals before forwarding the probe. This was accomplished by comparing data collected with a MIP system with (1) unheated transfer line and (2) a system including a heated transfer line to data collected with a system using (3) a depth‐dependent triggered sampling behind the membrane including two transfer lines. A comparison with analytical results from soil samples gave a good correlation for all three methods. Furthermore, it could be shown that the use of a heated transfer line has a time improvement of 30% compared to an unheated transfer line while the depth dependent triggered sampling using two separate transfer lines yielded a time improvement of over 90%. These results confirm the benefit of the latter method, particularly for the use in highly contaminated sediments.  相似文献   

UV‐Irradiation of the Antibiotic Sulfathiazole Surprisingly Leads to Former Antituberculotic Promizole          下载免费PDF全文

Astrid Spielmeyer  Myriam Heer  Siegrun A.I. Mohring  Heike Hausmann  Jessica Stahl  Manfred Kietzmann  Sebastian Dold  Bernhard Spengler  Gerd Hamscher 《洁净——土壤、空气、水》2015,43(4):490-495

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