Quantification of vertical density variations of salt-marsh vegetation     

Urs Neumeier 《Estuarine, Coastal and Shelf Science》2005,63(4):489-496

Density and structure of salt-marsh canopies control the reduction of water flow by the vegetation, which may cause inter alia increased accretion. This paper presents and evaluates two methods that quantify the vertical density variations of salt-marsh canopies: the vertical biomass distribution and the lateral obstruction ratio obtained from a binarised picture. The former provides accurate results and is well adapted to define canopy heights; the second reflects the flow hindrance better, but is unsuitable for dense canopies. Both methods are used to illustrate density variation over short distances in Spartina marshes and to monitor two English salt-marshes over one year. The results demonstrate the great seasonal variability in the vegetation, which must be taken into account when long-term predictions are extrapolated from short-term measurements.  相似文献   

Episodic construction of the Tatra granitoid intrusion (Central Western Carpathians,Poland/Slovakia): consequences for the geodynamics of Variscan collision and Rheic Ocean closure     

Aleksandra Gawęda  Jolanta Burda  Urs Klötzli  Jan Golonka  Krzysztof Szopa 《International Journal of Earth Sciences》2016,105(4):1153-1174

  相似文献   

The relative mobility of natural (Th,Pb and Po) and fallout (Pu,Am, Cs) radionuclides in the coastal marine environment: results from model ecosystems (MERL) and Narragansett Bay     

Peter H Santschi  Yuan-Hui Li  Dennis M Adler  Michael Amdurer  Joy Bell  Urs P Nyffeler 《Geochimica et cosmochimica acta》1983,47(2):201-210

The relative mobility of nuclides of Pb, Th, Pu, and Cs, which are widely used as geochemical tracers for sedimentation and bioturbation. was investigated in artificial microcosm tanks (MERL) and in Narragansett Bay. Their mobility was characterized by their removal rates from the water column, their affinity toward particles and their degree of penetration into the surface sediments. Pb, Th, and Pu transport was controlled predominantly by the affinity of these elements to particles, and the transport parameters of the particles themselves (i.e. sediment resuspension and mixing rates). Because of its low distribution coefficient, transport of Cs was controlled by molecular diffusion through pore water in the winter, while in summer, Cs transport was enhanced due to bioturbation. The increase with depth of the $\text{Cs}\text{Pu}$ ratio in core profiles of MERL and Narragansett Bay sediments is thus caused primarily by the higher mobility of Cs.  相似文献   

On the distribution of noble gases in Allende: a differential oxidation study     

Urs Frick  R.O. Pepin 《Earth and Planetary Science Letters》1981

We have developed a closed-system combustion technique and utilized it to progressively oxidize a gas-rich, highly carbonaceous acid residue and a fine-grained (<4 μm) matrix sample from the Allende C3V meteorite and analyze the released gases mass spectrometrically. For the residue complete gas mobilization occurs at temperatures below 600°C. The temperature interval over which most of the gases are released coincides with that for combustion of most of the carbon. Release is primarily due to chemical attack rather than thermal activation of the gases. There are somewhat different oxidation thresholds for the heavy gases (Ar, Kr, and Xe) and the light gases (He, Ne), indicating chemically different sites for the two groups. Relative enhancement of isotopically anomalous components near 600°C is as large as in any open-system oxidation method. Differential combustion of the matrix sample reveals three distinct outgassing peaks, the first matching the release from the carbonaceous residue (“combustibles”), the second attributed to sulfides, and the third tentatively assigned to silicates. They comprise about 53%, 7% and 40% of the total heavy gases respectively. While the “sulfides” exhibit a small fission-like component, the Xe in the “silicates” appears isotopically uniform with roughly AVCC composition. The “combustibles” of the matrix contain relatively less excess¹²⁹Xe than the residue, perhaps indicating that ～10% of the total¹²⁹Xe in the residue was acquired from “silicates” by redistribution during acid treatment. We cannot rule out the possibility that planetary gases assigned to “sulfides” or “silicates” actually reside in carbonaceous phases somehow sheltered within soluble mineral assemblages, or in acid-soluble carbonaceous phases resistant to oxidation. Integrated releases below and above 600°C during the matrix combustion exhibit virtually identical heavy gas elemental composition, implying similar fractionation during planetary gas entrapment in various materials or in the same material in various environments.  相似文献   

Osmium isotopes in the aerosols of the mantle volcano Mauna Loa   总被引：2，自引：0，他引：2  

Urs Kr  henbü  hl  Markus Geissbü  hler  Fritz Bü  hler  Peter Eberhardt  David L. Finnegan 《Earth and Planetary Science Letters》1992,110(1-4):95-98

Aerosols and reactive gases from the spring 1984 eruption of Mauna Loa Volcano on Hawaii were collected and analyzed for osmium and its isotopic composition. The measured¹⁸⁷Os/¹⁸⁶Os ratio of1.14 ± 0.03 is close to the ratio in matter with solar systemRe/Os abundance. This result shows that the aerosols from Mauna Loa originated in the mantle and that their composition was not or only slightly influenced by their contact with the crust.  相似文献   

Human impacts and eutrophication patterns during the past ~200 years at Lago Grande di Avigliana (N. Italy)     

Walter Finsinger  Christian Bigler  Urs Krähenbühl  André F. Lotter  Brigitta Ammann 《Journal of Paleolimnology》2006,36(1):55-67

A short sediment core from Lago Grande di Avigliana (Piedmont, Italy), the second most eutrophied lake in Italy, was analysed for pollen and diatoms to reconstruct land-use changes and to estimate baseline conditions for total phosphorus (TP) in the water column. Varve counts on sediment thin-sections and ²¹⁰Pb, ²²⁶Ra, and ¹³⁷Cs dating provided a reliable chronology for the past ~200 years. The main pollen-inferred land-use changes showed a sharp decrease of hemp retting around AD 1900, as well as a gradual change to less intensive agriculture and increasing abundance of exotic plants since AD ~1970. Diatom-inferred TP reconstructions indicated stable TP concentrations until AD ~1950, revealing baseline mesotrophic conditions (TP <25 μg l⁻¹). After AD ~1950, TP values increased distinctly and continuously, culminating in the late 1960s with concentrations of 150 μg l⁻¹. Subsequently, diatoms implied a linear decrease of TP, with an inferred value of 40 μg l⁻¹ in the surface sediment sample. Comparison with instrumental TP measurements from the water column since AD 1980 showed a rapid recovery and allowed a direct validation of the diatom TP inference. However, although the TP concentration has decreased considerably, baseline conditions have not yet been reached. When compared to the limnological effects of sewage discharges on inferred-TP concentration, our results indicated that agricultural land use played a minor role in the lake’s eutrophication.  相似文献   

Age and isotopic constraints on magmatism along the Karakoram-Kohistan Suture Zone,NW Pakistan: evidence for subduction and continued convergence after India-Asia collision   总被引：1，自引：0，他引：1  

Stefan Heuberger  Urs Schaltegger  Jean-Pierre Burg  Igor Maria Villa  Martin Frank  Hamid Dawood  Shahid Hussain  Andrea Zanchi 《Swiss Journal of Geoscience》2007,100(1):85-107

  相似文献   

Survival of eclogite xenolith in a Cretaceous granite intruding the Central Dabieshan migmatite gneiss dome (Eastern China) and its tectonic implications   总被引：3，自引：0，他引：3  

Wei Lin  Masaki Enami  Michel Faure  Urs Schärer  Nicolas Arnaud 《International Journal of Earth Sciences》2007,96(4):707-724

Investigation of an eclogite xenolith, discovered in a Cretaceous granite from the Central Domain of the Dabieshan massif in eastern China, yields new petrological insights into the high to ultrahigh-pressure metamorphism, experienced by the Qinling-Dabie orogen. Prior to inclusion as a xenolith in the granite during the Early Cretaceous, this eclogite xenolith had recorded a complex metamorphic evolution that complies with subduction and exhumation processes experienced by the continental crust of the South China Block. Well-preserved mineral parageneses substantiate the prograde and retrograde stages revealed by inclusions in porphyroblastic garnet and zoned minerals such as garnet, omphacite and amphibole in the matrix. The relatively low P/T re-equilibration during a late metamorphic stage was textually inferred by the presence of aluminous and calcic-subcalcic amphiboles such as katophorite, edenite, taramite and pargasite as main matrix phases. According to our U/Pb, Rb/Sr and new ⁴⁰Ar/³⁹Ar geochronological results, namely109 ± 1 and 112 ± 2 Ma plateau ages for muscovite and amphiboles, respectively, two successive but distinct cooling stages account for the thermal history of the granite–migmatite gneiss dome that forms the Central Dabieshan Domain. We argue that prior to the Cretaceous doming, the Central Dabieshan Domain experienced a tectono-metamorphic evolution similar to that observed in the high-pressure to ultra high-pressure units developed in the Southern Dabieshan Domain and Hong’an massif.  相似文献   

Zircon U–Pb geochronology of Ordovician magmatism in the polycyclic Ruitor Massif (Internal W Alps)     

François Guillot  Urs Schaltegger  Jean-Michel Bertrand  Étienne Deloule  Thierry Baudin 《International Journal of Earth Sciences》2006,95(1):1-1

  相似文献   

Automatic regional moment tensor inversion in the European-Mediterranean region   总被引：4，自引：0，他引：4  

Fabrizio Bernardi  Jochen Braunmiller  Urs Kradolfer  Domenico Giardini 《Geophysical Journal International》2004,157(2):703-716

  相似文献