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71.
Summary A flow-through chromatographic experiment was carried out to determine the ability of an oxidized, acidic, chloride-bearing
solution to transport Pd through a column of crushed Columbia River basalt at 25 °C. An initial plug of solution containing
13.8 mg Pd/kg H2O was loaded onto the column of crushed basalt and eluted with an air-saturated, 1 m NaCl solution of pH 3. Even after 3606 h
of elution, corresponding to a fluid-rock mass ratio of 1338, less than 10% of the Pd originally loaded on the column was
recovered. On the other hand, in a similar experiment involving relatively unreactive quartz sand, the Pd was almost completely
recovered after the passage of only 4 pore masses of eluent (or a fluid-rock mass ratio of approximately one), a behavior
similar to that of Rb. The results suggest that unrealistically large amounts of oxidizing and acidic fluids are required
to react with a given mass of basalt in order to overcome the acid- and redox-buffering capacity of the rock and to mobilize
palladium as a chloride complex. On the other hand, Pd-chloride complexes can be easily transported through a rock with minimal
acid- and redox-buffering capacity, such as clean quartz sandstone. The implications of this study for PGE enrichments in
sediment-hosted stratiform copper (Kupferschiefer type) deposits are explored briefly.
Authors’ addresses: Scott A. Wood, Department of Geological Sciences, University of Idaho, Box 443022, Moscow, Idaho 83844-3022, USA; Charles Normand, Département des Sciences de la Terre et de l’Atmosphère, Université du Québec à Montréal, Case postale 8888, Succursale
Centre-ville, Montréal (Québec), H3C 3P8 Canada 相似文献
72.
73.
Ian McCallum Wolfgang Wagner Christiane Schmullius Anatoly Shvidenko Michael Obersteiner Steffen Fritz Sten Nilsson 《Carbon balance and management》2009,4(1):8-14
Production efficiency models (PEMs) are based on the theory of light use efficiency (LUE) which states that a relatively constant
relationship exists between photosynthetic carbon uptake and radiation receipt at the canopy level. Challenges remain however
in the application of the PEM methodology to global net primary productivity (NPP) monitoring. The objectives of this review
are as follows: 1) to describe the general functioning of six PEMs (CASA; GLO-PEM; TURC; C-Fix; MOD17; and BEAMS) identified
in the literature; 2) to review each model to determine potential improvements to the general PEM methodology; 3) to review
the related literature on satellite-based gross primary productivity (GPP) and NPP modeling for additional possibilities for
improvement; and 4) based on this review, propose items for coordinated research. 相似文献
74.
75.
Christiane Hudon Antonella Cattaneo Anne-Marie Tourville Poirier Philippe Brodeur Pierre Dumont Yves Mailhot Jean-Pierre Amyot Simon-Pierre Despatie Yves de Lafontaine 《Aquatic Sciences - Research Across Boundaries》2012,74(3):495-511
Submerged aquatic vegetation (SAV) constitutes a major component of fish habitat, providing support for epiphytes and invertebrates as well as shelter from predators. The effects of wetland epuration from a mesotrophic to a nearly oligotrophic state were examined over a 15?km long reach of the St. Lawrence River under the direct influence of major farmland tributaries. We hypothesized that the nutrient-enriched zone would support a higher biomass of SAV, epiphytes, macroinvertebrates and fish than the nitrogen-deficient epurated zone located downstream of the wetland. Predictions included that the enriched habitat would support a richer fish assemblage, with higher biomass and growth of juvenile yellow perch than found in the epurated zone. Results supported these hypotheses, demonstrating the chain of effects of nutrient reduction on the biomass of SAV (fourfold drop), invertebrate prey (ninefold), small (threefold) and large (1.5-fold) fish between the two zones. In addition to the reduction in SAV biomass, the replacement of filamentous chlorophytes by benthic mats of filamentous cyanobacteria in the epurated zone resulted in a less complex 3-D habitat structure and a low invertebrate availability for fish. Oligotrophication by wetland epuration exerted negative effects on fish habitat quality, food quantity and availability, with an impairment of juvenile perch growth and recruitment. A generalized model of the changes in habitat carrying capacity occurring with epuration (oligotrophication) or eutrophication is presented, with examples of other aquatic systems in which strong linkages between trophic status, SAV, invertebrates and fish productivity were also demonstrated. 相似文献
76.
Are marine plastic particles transport vectors for organic pollutants to the Arctic? 总被引:2,自引:0,他引:2
Christiane Zarfl 《Marine pollution bulletin》2010,60(10):1810-10081
Plastic litter accounts for 50-80% of waste items stranded on beaches, floating on the ocean surface and lodged in the seabed. Organic pollutants can be absorbed onto plastic particles from sea water, attached to their surfaces or included in the plastic matrix as additives. Such chemicals may be transported to remote regions by buoyant plastics and ocean currents. We have estimated mass fluxes of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and perfluorooctanoic acid (PFOA) to the Arctic via the main ocean currents and compared them to those in the dissolved state and in air. Substance fluxes with atmospheric or sea water currents account for several tons per year, whereas those mediated by plastics are four to six orders of magnitude smaller. However, the significance of various pollutant transport routes does not depend only on absolute mass fluxes but also on bioaccumulation in marine food chains. 相似文献
77.
Complex resistivity and radar investigation of building material: First results of field scale measurements 总被引:1,自引:0,他引:1
Sabine Kruschwitz Ernst Niederleithinger Christiane Trela Jens Wöstmann 《Acta Geophysica》2010,58(1):96-113
Moisture ingress is one of major damaging factors for masonry buildings. As the complex resistivity (CR) is sensitive to textural
properties as well as to the pore fluid chemistry of wet porous media, its non-destructive application can provide helpful
information for conservators. In a comprehensive laboratory study it has been shown that CR might even be able to distinguish
between salt content and saturation degree in only one measurement. The combined use of electrical and electromagnetic measurement
techniques in two field-scale flooding experiments has shown some unexpected differences. Possible reasons are discussed and
it is shown that bringing together the information of both methods leads to a clearer picture. 相似文献
78.
Mark Reyers Andreas Krüger Christiane Werner Joaquim G. Pinto Stefan Zacharias Michael Kerschgens 《Boundary-Layer Meteorology》2011,139(1):121-141
A mesoscale meteorological model (FOOT3DK) is coupled with a gas exchange model to simulate surface fluxes of CO2 and H2O under field conditions. The gas exchange model consists of a C3 single leaf photosynthesis sub-model and an extended big
leaf (sun/shade) sub-model that divides the canopy into sunlit and shaded fractions. Simulated CO2 fluxes of the stand-alone version of the gas exchange model correspond well to eddy-covariance measurements at a test site
in a rural area in the west of Germany. The coupled FOOT3DK/gas exchange model is validated for the diurnal cycle at singular
grid points, and delivers realistic fluxes with respect to their order of magnitude and to the general daily course. Compared
to the Jarvis-based big leaf scheme, simulations of latent heat fluxes with a photosynthesis-based scheme for stomatal conductance
are more realistic. As expected, flux averages are strongly influenced by the underlying land cover. While the simulated net
ecosystem exchange is highly correlated with leaf area index, this correlation is much weaker for the latent heat flux. Photosynthetic
CO2 uptake is associated with transpirational water loss via the stomata, and the resulting opposing surface fluxes of CO2 and H2O are reproduced with the model approach. Over vegetated surfaces it is shown that the coupling of a photosynthesis-based
gas exchange model with the land-surface scheme of a mesoscale model results in more realistic simulated latent heat fluxes. 相似文献
79.
Mohammed A. Khairy Marit Kolb Christiane Schmidt Dieter W. Zachmann Alaa R. Mostafa Anwar A. EL‐Fiky Müfit Bahadir 《洁净——土壤、空气、水》2011,39(3):301-312
Sediment samples were collected from 30 different locations in Abu Qir Bay (Mediterranean Sea), East Alexandria, Egypt and analyzed for trace elements. The highest concentrations of most of the elements were observed in the nearshore stations in the vicinity of the major anthropogenic activities as industrial settlements, wastewater discharges, and agricultural drainage. In addition, mussel samples of Mactra corallina and Tapes decussata were collected corresponding to the sediment samples. Concentrations of As, Cd, Cr, Mn, and Zn in the mussel tissues were higher than concentrations in sediments, thus indicating their relatively high bioavailability. Sequential extraction procedure was performed on selected sediment samples. Significant correlations were observed between the concentrations of Cu, Mn, Pb, and Zn in the exchangeable fraction of the sediments and the corresponding tissues of M. corallina. The output of the risk assessment applied on the sediments revealed that adverse ecological effects to benthic species could occur and that a higher level of risk is expected from the exposure to Cd, Cr, Hg, and Zn. No adverse carcinogenic or non‐carcinogenic human health effects are expected from the consumption of the two mussel species from Abu Qir Bay. 相似文献
80.
Bianchi TS Cook RL Perdue EM Kolic PE Green N Zhang Y Smith RW Kolker AS Ameen A King G Ojwang LM Schneider CL Normand AE Hetland R 《Marine environmental research》2011,72(5):248-257
Here we present results of an initial assessment of the impacts of a water diversion event on the concentrations and chemical composition of dissolved organic matter (DOM) and bacterioplankton community composition in Barataria Bay, Louisiana U.S.A, an important estuary within the Mississippi River Delta complex. Concentrations and spectral properties of DOM, as reflected by UV/visible absorbance and fluorescence, were strikingly similar at 26 sites sampled along transects near two western and two eastern areas of Barataria Bay in July and September 2010. In September 2010, dissolved organic carbon (DOC) was significantly higher (568.1-1043 μM C, x=755.6+/-117.7 μM C, n=14) than in July 2010 (249.1-577.1 μM C, x=383.7+/-98.31 μM C, n=14); conversely, Abs254 was consistently higher at every site in July (0.105-0.314) than in September (0.080-0.221), averaging 0.24±0.06 in July and 0.15±0.04 in September. Fluorescence data via the fluorescence index (FI450/500) revealed that only 30% (8 of 26) of the July samples had an FI450/500 above 1.36, compared to 96% (25 of 26) for the September samples. This indicates a more terrestrial origin for the July DOM. Bacterioplankton from eastern sites differed in composition from bacterioplankon in western sites in July. These differences appeared to result from reduced salinities caused by the freshwater diversion. Bacterioplankton communities in September differed from those in July, but no spatial structure was observed. Thus, the trends in bacterioplankton and DOM were likely due to changes in water masses (e.g., input of Mississippi River water in July and a return to estuarine waters in September). Discharge of water from the Davis Pond Freshwater Diversion (DPFD) through Barataria Bay may have partially mitigated some adverse effects of the oil spill, inasmuch as DOM is concerned. 相似文献