Optimization of the Sampling Technique for the Determination of Dissolved Hydrogen in Groundwater     

Axel Heimann  Silke Marczinek  Karin Kloosb  Stefan Peiffer 《洁净——土壤、空气、水》2003,31(6):491-500

In this study a field‐sampling technique for dissolved hydrogen (H₂) in groundwater will be presented which allows the transport of gaseous samples into the laboratory for further analysis. The method consists of transferring the headspace trapped in a gas‐sampling bulb which is continuously purged by groundwater into previously evacuated vials using a gas‐tight syringe. Three transfer steps with preceding evacuation of the vial led to a H₂‐recovery of 100 % in laboratory experiments. The method has been applied to determine H₂ concentrations in an aquifer contaminated with chlorinated solvents. Tests concerning the effect of different pumping techniques on H₂ concentrations revealed that most reliable values were obtained with a bladder pump, while an electrically driven submersible pump generated considerable amounts of hydrogen due to electrochemical interactions with the sampled water. Concentrations of dissolved hydrogen in field and laboratory samples were about two orders of magnitude higher when sampling was performed with the electrically driven submersible pump compared to sampling with the bladder pump and a peristaltic pump. Lab experiments with a Plexiglas reservoir to produce H₂‐enriched water were used to study the effect of two tubing materials (PVC, polyamide) on H₂ losses. PVC tubing turned out to allow transfer of H₂‐enriched water over 25 m without significant losses, while PA‐tubing was not suitable for sampling of H₂.  相似文献   

Lower crustal melting and the role of open-system processes in the genesis of syn-orogenic quartz diorite–granite–leucogranite associations: constraints from Sr–Nd–O isotopes from the Bandombaai Complex, Namibia     

Tina van de Flierdt  Stephan Hoernes  Stefan Jung  Peter Masberg  Edgar Hoffer  Urs Schaltegger  Hans Friedrichsen 《Lithos》2003,67(3-4):205-226

The Bandombaai Complex (southern Kaoko Belt, Namibia) consists of three main intrusive rock types including metaluminous hornblende- and sphene-bearing quartz diorites, allanite-bearing granodiorites and granites, and peraluminous garnet- and muscovite-bearing leucogranites. Intrusion of the quartz diorites is constrained by a U–Pb zircon age of 540±3 Ma.

Quartz diorites, granodiorites and granites display heterogeneous initial Nd- and O isotope compositions (_{Nd (540 Ma)}=−6.3 to −19.8; δ¹⁸O=9.0–11.6‰) but rather low and uniform initial Sr isotope compositions (⁸⁷Sr/⁸⁶Sr_initial=0.70794–0.70982). Two leucogranites and one aplite have higher initial ⁸⁷Sr/⁸⁶Sr ratios (0.70828–0.71559), but similar initial _Nd (−11.9 to −15.8) and oxygen isotope values (10.5–12.9‰). The geochemical and isotopic characteristics of the Bandombaai Complex are distinct from other granitoids of the Kaoko Belt and the Central Zone of the Damara orogen. Our study suggests that the quartz diorites of the Bandombaai Complex are generated by melting of heterogeneous mafic lower crust. Based on a comparison with results from amphibolite-dehydration melting experiments, a lower crustal garnet- and amphibole-bearing metabasalt, probably enriched in K₂O, is a likely source rock for the quartz diorites. The granodiorites/granites show low Rb/Sr (<0.6) ratios and are probably generated by partial melting of meta-igneous (intermediate) lower crustal sources by amphibole-dehydration melting. Most of the leucogranites display higher Rb/Sr ratios (>1) and are most likely generated by biotite-dehydration melting of heterogeneous felsic lower crust. All segments of the lower crust underwent partial melting during the Pan-African orogeny at a time (540 Ma) when the middle crust of the central Damara orogen also underwent high T, medium P regional metamorphism and melting. Geochemical and isotope data from the Bandombaai Complex suggest that the Pan-African orogeny in this part of the orogen was not a major crust-forming episode. Instead, even the most primitive rock types of the region, the quartz diorites, represent recycled lower crustal material.  相似文献   

Effect of melt composition on the partitioning of trace elements between titanite and silicate melt   总被引：7，自引：0，他引：7  

Stefan Prowatke  Stephan Klemme 《Geochimica et cosmochimica acta》2005,69(3):695-709

Isobaric and isothermal experiments were performed to investigate the effect of melt composition on the partitioning of trace elements between titanite (CaTiSiO₅) and a range of different silicate melts. Titanite-melt partition coefficients for 18 trace elements were determined by secondary ion mass spectrometry (SIMS) analyses of experimental run products. The partition coefficients for the rare earth elements and for Th, Nb, and Ta reveal a strong influence of melt composition on partition coefficients, whereas partition coefficients for other studied monovalent, divalent and most quadrivalent (i.e., Zr, Hf) cations are not significantly affected by melt composition. The present data show that the influence of melt composition may not be neglected when modelling trace element partitioning.It is argued that it is mainly the change of coordination number and the regularity of the coordination space of trace elements in the melt structure that controls partition coefficients in our experiments. Furthermore, our data also show that the substitution mechanism by which trace elements are incorporated into titanite crystals may be of additional importance in this context.  相似文献   

Partitioning of trace elements between rutile and silicate melts: Implications for subduction zones   总被引：9，自引：0，他引：9  

Stephan Klemme  Stefan Prowatke  Detlef Günther 《Geochimica et cosmochimica acta》2005,69(9):2361-2371

Mineral/melt trace element partition coefficients were determined for rutile (TiO₂) for a large number of trace elements (Zr, Hf, Nb, Ta, V, Co, Cu, Zn, Sr, REE, Cr, Sb, W, U, Th). Whilst the high field strength elements (Zr, Hf, Nb, Ta) are compatible in rutile, other studied trace elements are incompatible (Sr, Th, REE). In all experiments we found D_Ta > D_Nb, D_Hf > D_Zr and D_U > D_Th. Partition coefficients for some polyvalent elements (Sb, W, and Co) were sensitive to oxygen fugacity. Melt composition exerts a strong influence on HFSE partition coefficients. With increasing polymerization of the melt, rutile/melt partition coefficients for the high field strength elements Zr, Hf, Nb and Ta increase about an order of magnitude. However, D_Nb/D_Ta and D_Hf/D_Zr are not significantly affected by melt composition. Because D_U ? D_Th, partial melting of rutile-bearing eclogite in subducted lithosphere may cause excesses of ²³⁰Th over ²³⁸U in some island arc lavas, whereas dehydration of subducted lithosphere may cause excesses of ²³⁸U over ²³⁰Th. From our partitioning results we infer partition coefficients for protactinium (Pa) which we predict to be much lower than previously anticipated. Contrary to previous studies, our data imply that rutile should not significantly influence observed ²³¹Pa-²³⁵U disequilibria in certain volcanic rocks.  相似文献   

Experimental characterization of the impact of temperature and humidity on the breakdown of soil water repellency in sandy soils and composts          下载免费PDF全文

Amii Whelan  Cedric Kechavarzi  Frederic Coulon  Stefan H. Doerr 《水文研究》2015,29(8):2065-2073

Soil water repellency is a widespread phenomenon with the capacity to alter hydrological and geomorphological processes. Water repellency decays with time, and the consequences are only of concern during the timescale at which the water repellency persists. This study aimed to characterize the influence of temperature and humidity on the breakdown of water repellency. Apparent contact angle measurements were carried out on samples consisting of sand treated with stearic acid as well as naturally repellent dune sands and composts. Temperature and humidity were controlled using a cooled incubator and a purpose designed enclosed box in which humidity could be raised or lowered. Results showed the contact angle of the stearic‐acid‐treated sands decayed with time and that there was a significant increase with stearic acid concentration. For all samples, the decay in apparent contact angle could be described with a continuous breakdown model. The stearic‐acid‐treated sands showed a significant increase in contact angle with relative humidity at a temperature of 10 and 20 °C. These differences diminished with increasing temperature. Similar results were seen for the dune sands and composts. Despite the influence of temperature and humidity on contact angles, there was no significant change in the rate at which the contact angle decayed in any sample. Absolute humidity was found to provide a more relevant indicator than relative humidity when assessing the influence of humidity on repellency over a range of temperatures. The contact angle initially increased with absolute humidity before plateauing owing to the confounding effect of temperature. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Towards more systematic perceptual model development: a case study using 3 Luxembourgish catchments          下载免费PDF全文

Sebastian Wrede  Fabrizio Fenicia  Núria Martínez‐Carreras  Jérôme Juilleret  Christophe Hissler  Andreas Krein  Hubert H. G. Savenije  Stefan Uhlenbrook  Dmitri Kavetski  Laurent Pfister 《水文研究》2015,29(12):2731-2750

The synthesis of experimental understanding of catchment behaviour and its translation into qualitative perceptual models is an important objective of hydrological sciences. We explore this challenge by examining the cumulative understanding of the hydrology of three experimental catchments and how it evolves through the application of different investigation techniques. The case study considers the Huewelerbach, Weierbach and Wollefsbach headwater catchments of the Attert basin in Luxembourg. Subsurface investigations including bore holes and pits, analysis of soil samples and Electrical Resistivity Tomography measurements are presented and discussed. Streamflow and tracer data are used to gain further insights into the streamflow dynamics of the catchments, using end‐member mixing analysis and hydrograph separation based on dissolved silica and electrical conductivity. We show that the streamflow generating processes in all three catchments are controlled primarily by the subsolum and underlying bedrock. In the Huewelerbach, the permeable sandstone formation supports a stable groundwater component with little seasonality, which reaches the stream through a series of sources at the contact zone with the impermeable marls formation. In the Weierbach, the schist formation is relatively impermeable and supports a ‘fill and spill’‐type of flow mechanism; during wet conditions, it produces a delayed response dominated by pre‐event water. In the Wollefsbach, the impermeable marls formation is responsible for a saturation‐excess runoff generating process, producing a fast and highly seasonal response dominated by event water. The distinct streamflow generating processes of the three catchments are represented qualitatively using perceptual models. The perceptual models are in turn translated into quantitative conceptual models, which simulate the hydrological processes using networks of connected reservoirs and transfer functions. More generally, the paper illustrates the evolution of perceptual models based on experimental fieldwork data, the translation of perceptual models into conceptual models and the value of different types of data for processes understanding and model representation. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

New major element analyses of proximal tephras from the Azores and suggested correlations with cryptotephras in North-West Europe     

Stefan Wastegård  Hans Johansson  José M. Pacheco 《第四纪科学杂志》2020,35(1-2):114-121

The Azores Archipelago is one of the most active volcanic areas in the North Atlantic region. Approximately 30 eruptions have been reported over the last 600 years with some major VEI 5 (Volcanic Explosivity Index) eruptions further back in time. The geochemical composition of associated tephra-derived glass, however, is not well characterized. An Azorean origin of cryptotephras found in distal areas such as North Africa, the British Isles and Greenland has been suggested, but proximal data from the Azores are scarce and the correlations have only been tentative. These tephras have a traychtic composition, which excludes an Icelandic origin. In a previous study, we presented major element analyses of proximal tephra-derived glass from five Holocene eruptions on the Azores Islands. There is a striking geochemical similarity between tephras from volcanoes on São Miguel and Irish cryptotephras, and especially with eruptives from the Furnas volcano. Here we present new analyses of proximal tephras that confirm and strengthen a link between Furnas and cryptotephras found in south-west Ireland. We also suggest a correlation between a previously unsourced tephra found in a Swedish bog with an eruption of the Sete Cidades volcano c. 3880 a cal BP.  相似文献   

Exploring hydroclimatic change disparity via the Budyko framework          下载免费PDF全文

Ype van der Velde  Nikki Vercauteren  Fernando Jaramillo  Stefan C. Dekker  Georgia Destouni  Steve W. Lyon 《水文研究》2014,28(13):4110-4118

The Budyko framework characterizes landscape water cycles as a function of climate. We used this framework to identify regions with contrasting hydroclimatic change during the past 50 years in Sweden. This analysis revealed three distinct regions: the mountains, the forests, and the areas with agriculture. Each region responded markedly different to recent climate and anthropogenic changes, and within each region, we identified the most sensitive subregions. These results highlight the need for regional differentiation in climate change adaptation strategies to protect vulnerable ecosystems and freshwater resources. Further, the Budyko curve moved systematically towards its water and energy limits, indicating augmentation of the water cycle driven by changing vegetation, climate and human interactions. This finding challenges the steady state assumption of the Budyko curve and therefore its ability to predict future water cycles. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

The Late Cretaceous Klepa basalts in Macedonia (FYROM)—Constraints on the final stage of Tethys closure in the Balkans          下载免费PDF全文

Dejan Prelević  Simon Wehrheim  Magnus Reutter  Rolf L. Romer  Blažo Boev  Milica Božović  Paul van den Bogaard  Vladica Cvetković  Stefan M. Schmid 《地学学报》2017,29(3):145-153

The waning stage(s) of the Tethyan ocean(s) in the Balkans are not well understood. Controversy centres on the origin and life‐span of the Cretaceous Sava Zone, which is allegedly a remnant of the last oceanic domain in the Balkan Peninsula, defining the youngest suture between Eurasia‐ and Adria‐derived plates. In order to investigate to what extent Late‐Cretaceous volcanism within the Sava Zone is consistent with this model we present new age data together with trace‐element and Sr–Nd–Pb isotope data for the Klepa basaltic lavas from the central Balkan Peninsula. Our new geochemical data show marked differences between the Cretaceous Klepa basalts (Sava Zone) and the rocks of other volcanic sequences from the Jurassic ophiolites of the Balkans. The Klepa basalts mostly have Sr–Nd–Pb isotopic and trace‐element signatures that resemble enriched within‐plate basalts substantially different from Jurassic ophiolite basalts with MORB, BAB and IAV affinities. Trace‐element modelling of the Klepa rocks indicates 2%–20% polybaric melting of a relatively homogeneously metasomatised mantle source that ranges in composition from garnet lherzolite to ilmenite+apatite bearing spinel–amphibole lherzolite. Thus, the residual mineralogy is characteristic of a continental rather than oceanic lithospheric mantle source, suggesting an intracontinental within‐plate origin for the Klepa basalts. Two alternative geodynamic models are internally consistent with our new findings: (1) if the Sava Zone represents remnants of the youngest Neotethyan Ocean, magmatism along this zone would be situated within the forearc region and triggered by ridge subduction; (2) if the Sava Zone delimits a diffuse tectonic boundary between Adria and Europe which had already collided in the Late Jurassic, the Klepa basalts together with a number of other magmatic centres represent volcanism related to transtensional tectonics.  相似文献   

Effect of bed surface roughness on longitudinal dispersion in artificial open channels     

Marcus Schulz  Jan Priegnitz  Jörg Klasmeier  Stefan Heller  Stefan Meinecke  Michael Feibicke 《水文研究》2012,26(2):272-280

In several empirical and modelling studies on river hydraulics, dispersion was negatively correlated to surface roughness. In this study, it was aimed to investigate the influence of surface roughness on longitudinal dispersion under controlled conditions. In artificial flow channels with a length of 104 m, tracer experiments with variations in channel bed material were performed. By use of measured tracer breakthrough curves, average flow velocity, mean longitudinal dispersion, and mean longitudinal dispersivity were calculated. Longitudinal dispersion coefficients ranged from 0·018 m² s^?1 in channels with smooth bed surface up to 0·209 m² s^?1 in channels with coarse gravel as bed material. Longitudinal dispersion was linearly related to mean flow velocity. Accordingly, longitudinal dispersivities ranged between 0·152 ± 0·017 m in channels with smooth bed surface and 0·584 ± 0·015 m in identical channels with a coarse gravel substrate. Grain size and surface roughness of the channel bed were found to correlate positively to longitudinal dispersion. This finding contradicts several existing relations between surface roughness and dispersion. Future studies should include further variation in surface roughness to derive a better‐founded empirical equation forecasting longitudinal dispersion from surface roughness. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献