排序方式： 共有90条查询结果，搜索用时 578 毫秒
61.
José Antonio Álvarez-Robles Miguel Ángel Latre Pedro Rafael Muro-Medrano Francisco Javier Zarazaga-Soria Ruben Béjar 《Transactions in GIS》2007,11(6):835-847
This article aims at providing a simple way for water quality monitoring in a set of reservoirs using an earth observation‐based approach and the assessment of the use of this technique for a monitoring network in order to meet the requirements and objectives of the Water Framework Directive (WFD) by the Member States of the European Union. The study carried out was preformed in 42 reservoirs of the Ebro River Basin, in the northeast of Spain. The proposed methodology is based on the development of an algorithm for the estimation of water quality by means of LANDSAT TM band reflectance. Some band ratios were used in the model as well. Trophic State Index (TSI), calculated by means of Secchi Disc Transparency data, was estimated using a forward stepwise multiple regression analysis and the TM2 band and TM1/TM2 ratio. The final results showed a large variability in water quality across reservoirs. Moreover, substantial spatial heterogeneity was also observed in the water bodies. These results demonstrate the likelihood of developing a monitoring network based on remote sensing techniques for the implementation of the WFD. 相似文献
62.
Distribution and speciation of arsenic around roots in a contaminated riparian floodplain soil: Micro-XRF element mapping and EXAFS spectroscopy 总被引：4，自引：0，他引：4
Andreas Voegelin Frank-Andreas Weber Ruben Kretzschmar 《Geochimica et cosmochimica acta》2007,71(23):5804-5820
Riparian soils are periodically flooded, leading to temporarily reducing conditions. Diffusion of O2 through plants into the rhizosphere maintains oxic conditions around roots, thereby promoting trace element fractionation along a redox gradient from the reduced soil matrix towards the oxic rhizosphere. The aim of this study was to determine the distribution and speciation of arsenic around plant roots in a contaminated (170-280 mg/kg As) riparian floodplain soil (gleyic Fluvisol). The analysis of soil thin sections by synchrotron micro-X-ray fluorescence (μ-XRF) spectrometry showed that As and Fe were enriched around roots and that As was closely correlated with Fe. Arsenic contents of three manually separated rhizosphere soil samples from the subsoil were 5-9 times higher than respective bulk As contents. This corresponds to the accumulation of about half of the total As in the subsoil in Fe-enrichments around roots. The speciation of As in the soil was assessed by oxalate extractions at pH 3.0 as well as by X-ray absorption near edge structure (XANES) and extended X-ray fine structure (EXAFS) spectroscopy. More than 77% of the total As was oxalate extractable in all samples. XANES and EXAFS spectra demonstrated that As was predominantly As(V). For the accurate analysis of the EXAFS data with respect to the bonding of As(V) to the Fe- or Al-octahedra of (hydr)oxides and clays, all 3-leg and 4-leg multiple scattering paths within the As(V)O4-tetrahedron were considered in a fully constrained fitting scheme. We found that As(V) was predominantly associated with Fe-(hydr)oxides, and that sorption to Al- and Mn-hydroxides was negligible. The accumulation of As in the rhizosphere may affect As uptake by plants. Regarding the mobility of As, our results suggest that by oxygenation of the rhizosphere, plants attenuate the leaching of As from riparian floodplain soils during periods of high groundwater levels or flooding. 相似文献
63.
64.
Ruben D. Kos&#x;yan 《Coastal Engineering》1985,9(2):171-187
On the basis of the current concepts on the wave flow structure and solid particle motion in turbulent flow, an equation was derived which enables the suspended sediment concentration profile to be computed from known wave parameters. The equation was verified by laboratory and full-scale experiments which proved that it can be implemented for practical computations of the concentration profile seawards of the breaking zone. The formula yields the best results when operating on wave characteristics corresponding to maximum spectral density. 相似文献
65.
Göril Möschner Barbara Lothenbach Andrea Ulrich Ruben Kretzschmar 《Geochimica et cosmochimica acta》2008,72(1):1-18
The solubility of Fe-ettringite (Ca6[Fe(OH)6]2(SO4)3 · 26H2O) was measured in a series of precipitation and dissolution experiments at 20 °C and at pH-values between 11.0 and 14.0 using synthesised material. A time-series study showed that equilibrium was reached within 180 days of ageing. After equilibrating, the solid phases were analysed by XRD and TGA while the aqueous solutions were analysed by ICP-OES (calcium, sulphur) and ICP-MS (iron). Fe-ettringite was found to be stable up to pH 13.0. At higher pH-values Fe-monosulphate (Ca4[Fe(OH)6]2(SO4) · 6H2O) and Fe-monocarbonate (Ca4[Fe(OH)6]2(CO3) · 6H2O) are formed. The solubilities of these hydrates at 25 °C are: 相似文献
66.
67.
Primary production, plant and detrital biomass, and particle transport in the Columbia River Estuary
Lawrence F. Small C.David McIntire Keith B. MacDonald J.Ruben Lara-Lara Bruce E. Frey Michael C. Amspoker Ted Winfield 《Progress in Oceanography》1990,25(1-4)
The dynamics of primary production and particulate detritus cycling in the Columbia River Estuary are described, with particular reference to mechanisms that account for patterns within the water column, on the tidal flats, and in the adjacent wetlands. Analysis of patterns in phytoplankton flora and biomass and in distribution of detrital particulate organic matter (DPOC) in the water column indicated that salinities of 1–5 delineated an essentially freshwater flora from a marine or euryhaline flora, and that living phytoplankton was converted to DPOC at the freshwater-brackishwater interface. Similarly, the benthic diatom assemblages on tidal flats reflected either the fresh or the brackish nature of the water inundating the flats. Emergent vascular plants were grouped into six associations by cluster analysis, the associations being separated mainly on the bases of different relative abundances of freshwater, euryhaline or brackishwater species, and on whether samples occurred in high or low marsh areas.Annual rates of net areal 24-hr production averaged 55, 16, and 403gC m−2y−1 for phytoplankton, benthic algae, and emergent vascular vegetation, respectively. Total production over the whole estuary was 17,667 metric tons C y−1 for phytoplankton, 1,545mt C y−1 for benthic algae, and 11,325mt C y−1 for emergent vascular plants, for a grand total to 30,537mt C y−1. Phytoplankton biomass turned over approximately 39 times per year on average, while benthic algae turned over about twice and emergent plants once per year.Budgets for phytoplankton carbon (PPOC) and DPOC were developed based on PPOC and DPOC import and export, grazing loss, and in situ production and conversion of PPOC to DPOC. It is suggested that 36,205mt y−1 of PPOC is converted to DPOC in the estuary, principally at the freshwater-brackishwater interface. About 40,560mt y−1 of PPOC is exported to the ocean, and 159,185mt y−1 of DPOC is transported into the marine zone of the estuary (no data are available on DPOC export to the ocean). Thus, the estuary acts principally as a conduit for the transport of particles to the sea, and only secondarily as a converter of viable phytoplankton cells to detrital carbon and as a trap for DPOC. 相似文献
68.
Rafael García-Ruiz Avto Goguitchaichvili Miguel Cervantes-Solano Juan Morales Rafael Maciel-Peña José Rosas-Elguera Ruben Cejudo-Ruiz Jaime Urrutia-Fucugauchi 《Studia Geophysica et Geodaetica》2017,61(2):249-263
A rock magnetic and paleomagnetic investigation was performed on some selected, radiometrically dated lava flows from the Mascota Volcanic Field (MVF), western Trans- Mexican Volcanic Belt. A set of rock-magnetic experiments and standard paleomagnetic analysis were carried out on 19 sites spanning the time interval from 2268 to 72 kyr. The paleomagnetic directions are anchored to absolute radiometric ages while no such information was available in previous studies. This makes possible to correctly evaluate the fluctuation of Earth’s magnetic field from Pliocene to Pleistocene and reveal the firm evidence of possible Levantine excursion. Both Ti-poor and Ti-rich titanomagnetites seem to carry the remanent magnetization with Curie temperatures ranging from 350°C to 537°C. Thirteen flows correspond to the Brunhes chron, one of them exhibits transitional directions, while the remaining six sites belong to the Matuyama chron. New and existing dataset for MVF were used to estimate the paleosecular variation parameters. The selected data include 35 Plio-Quaternary lava flows. After excluding the poor quality data, as well as the transitional directions, the mean paleodeclination is 356.1° and oaleoinclination 39.9°, which agree well with the geocentric axial dipole (GAD) and the expected paleodirections for the Plio-Pleistocene, as derived from the reference poles for the stable North America. The corresponding mean paleomagnetic poles are paleolongitude 226.7° and paleolatitude 86.0°. The virtual geomagnetic pole scatter for the MVF is 15.2°, which is consistent with the value expected from model G at latitude of 20° (this model provides an interpretation of the paleosecular variation at different latitudes for the time of interest). The combined paleomagnetic data, supported by positive reversal test, indicate no paleomagnetically detectable vertical-axis rotations in the study area. The evidence of one transitional directions was detected, which may correspond to the Levantine excursion (360-370 kyr) or unnamed event between 400-420 kyr. 相似文献
69.
Marie-Laure Pesch Iso Christl Kurt Barmettler Stephan M Kraemer Ruben Kretzschmar 《Geochemical transactions》2011,12(1):2
Background
The isolation of highly pure copper-free methanobactin is a prerequisite for the investigation of the biogeochemical functions of this chalkophore molecule produced by methane oxidizing bacteria. Here, we report a purification method for methanobactin from Methylosinus trichosporium OB3b cultures based on reversed-phase HPLC fractionation used in combination with a previously reported resin extraction. HPLC eluent fractions of the resin extracted product were collected and characterized with UV-vis, FT-IR, and C-1s NEXAFS spectroscopy, as well as with elemental analysis and ESI-MS. 相似文献70.
Olivier Jacquat Claire Rambeau Andreas Voegelin Natalia Efimenko André Villard Karl B. Föllmi Ruben Kretzschmar 《Swiss Journal of Geoscience》2011,104(3):409-424
In order to better understand the origin and enrichment mechanisms leading to elevated Zn concentrations in Jurassic limestone
of the Jura mountain range (JMR) and the Burgundy (B), we investigated four locations of Bajocian age (JMR: Lausen–Schleifenberg,
Gurnigel; B: Vergisson–Davayé, Lucy-le-Bois) and two locations of Oxfordian age (JMR: Dornach, Pichoux) for their Zn distribution
and speciation. Measurements of the acid-extractable and bulk Zn contents showed that Zn is stratigraphically and spatially
heterogeneously distributed, in association with permeable carbonate levels. Up to 3,580 and 207 mg/kg Zn was detected in
Bajocian and Oxfordian limestone, respectively, with numerous limestone samples having Zn contents above 50 mg/kg. Using X-ray
absorption near edge structure spectroscopy and micro-X-ray fluorescence spectrometry, the speciation and micro-scale distribution
of Zn was investigated for selected limestone samples. In Bajocian limestone sphalerite and/or Zn-substituted goethite and
a minor fraction of Zn-bearing carbonates were identified. In contrast, Zn-bearing carbonates (Zn-substituted calcite and
hydrozincite) were accounting for most of the total Zn in Oxfordian limestone. The micro-scale distribution of Zn for Bajocian
and Oxfordian limestone was however similar with localized Zn-rich zones in the limestone cement and at the rim of oolites.
The stratigraphic sporadicity and microscale heterogeneity of the Zn distribution together with the Zn speciation results
point to a hydrothermal origin of Zn. Occurence of Zn-goethite is probably linked to the oxidative transformation of framboidal
pyrite and hydrothermal sphalerite in contact with meteoritic waters. Difference in speciation between Bajocian limestone
and Oxfordian limestone may be related to differences in rock permeability and/or to various hydrothermal events. Isotopic
dating of the different mineralizations will be needed to decipher differences in Zn speciation and the precise chronology
of hydrothermal episodes. 相似文献