Influence of catchment quality and altitude on the water and sediment composition of 68 small lakes in Central Europe     

Beat Müller  André F. Lotter  Michael Sturm  Adrian Ammann 《Aquatic Sciences - Research Across Boundaries》1998,60(4):316-337

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The accessibility of big towns in FranceL'accessibilité des grandes villes françaisesZur erreichbarkeit der großen städte in Frankreich     

Jacqueline Beaujeu-Garnier  Odile Andan  André Libault 《Geoforum》1975,6(2):137-150

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Reflectance spectrophotometry extended to u.v. for terrestrial,lunar and meteoritic samples     

Audouin Dollfus  André Cailleux  Bernard Cervelle  Chon Trung Hua  Jean-Claude Mandeville 《Geochimica et cosmochimica acta》1980,44(9):1293-1310

Extension of remote sensing of planetary bodies to the ultraviolet is now feasiable up to 2000 Å from earth-orbiting telescopes and spacecraft. The benefits of this extension is analysed on the basis of laboratory spectra taken on a large variety of terrestrial, lunar and meteoritic samples. Knowledge of the albedo for two wavelengths at 2300 and 6500 Å permits classification of a surface into one of the following types: lunar, carbonaceous chondrites, ordinary chondrites, achondrites or acidic rocks, basaltic rocks, irons. For lunar-type surfaces, a simple albedo measurement at 6500 Å can be converted into quantitative abundance determinations of silicate, aluminium oxide and iron; a large amount of telescopic lunar photometry data is available for mapping these abundances. Extension of the photometry to 2300 Å permits quantitative measurement of TiO₂ abundances. For asteroids and non-icy satellites, rock-type classification and constraints in chemical abundances of Si, Al, Fe and Ti can be derived from photometry at 2300 and 6500 Å. The IUE telescope already orbiting the earth, the Space Telescope to come, the lunar polar orbiter and other spacecraft under prospect are potentially available to provide the photometric observations at 6500 and 2300 Å required.  相似文献   

Radiocarbon dates and late-Quaternary stratigraphy from Mamontova Gora,unglaciated central Yakutia,Siberia, U.S.S.R.     

Troy L. Péwé  André Journaux  Robert Stuckenrath 《Quaternary Research》1977,8(1):51-63

A fine exposure of perennially frozen ice-rich silt and associated flora and vertebrate fauna of late-Quaternary age exists at Mamontova Gora along the Aldan River in central Yakutia, Siberia, U.S.S.R. The silt deposit caps a 50-m-high terrace and consists of three units. An upper layer 1–2 m thick overlies a 10–15-m-thick brownish to black silt layer. The lower silt layer is greenish to gray and about 15 m thick. All the silt is well sorted with 60% of the particles falling between 0.005 and 0.5 mm in diameter and is generally chemically and mineralogically homogeneous. The middle unit contains may extinct vertebrate mammal remains and ice wedges. The lower unit contains little vegetation and no ice wedges. The silt is widespread and exists as a loamy blanket on terraces at various elevations on both sides of the lower Aldan River. The origin of the silt blanket of late-Quaternary age in central Yakutia has long been controversial. Various hypotheses have been suggested, including lacustrine and alluvial, as well as frost-action origins. It is sometimes referred to as loess-like loam. Péwé believes the silt at Mamontova Gora is loess, some of which has been retransported very short distances by water. The silt probably was blown from wide, braided, unvegetated flood plains of rivers draining nearby glaciers. The silt deposits are late Quaternary in age and probably associated with the Maximum glaciation (Samarov) and Sartan and Syryan glaciations of Wisconsinan age. On the basis of biostratigraphy, 10 radiocarbon dates, and their relation to the nearby glacial record, it is felt that the upper unit at Mamontova Gora is Holocene and the middle unit is Wisconsinan. The youngest date available from the middle unit at this particular location is 26,000 years. Dates greater than 56,000 years were obtained in the lower part of the middle unit. The lower unit is definitely beyond the range of radiocarbon dating and probably is older than the last interglacial. The sediment, fauna, ice wedges, stratigraphy, and age of perennially frozen slit deposits in central Alaska are remarkably similar to those of the deposits exposed in central Yakutia. Both areas consist of unglaciated rolling lowlands and river terraces surrounded by high mountains that were extensively glaciated in Pleistocene time. The glaciers extended from the high mountains to the edges of the ranges. In both regions, extensively braided, silt-charged rivers drained the mountains and flowed through the lowlands on their way to the sea. It follows that there should be a similar late-Quaternary history.  相似文献   

Precipitation water storage capacity in a temperate mixed oak–beech canopy     

Frédéric André  Mathieu Jonard  Quentin Ponette 《水文研究》2008,22(20):4130-4141

The storage capacity of a temperate mixed oak–beech stand was investigated as a function of stand density and species composition. Measurements were performed in selected zones delimited by three neighbouring trees. Three independent approaches were compared: (i) a spraying laboratory experiment to estimate the water storage on foliage before and after dripping; (ii) a mechanistic model describing rainfall partitioning within the forest canopy and providing estimates of foliage storage capacities; and (iii) linear regression analyses to evaluate the canopy (foliage + branches) storage capacity using the relationship between throughfall and rainfall. Good agreement was generally observed between the laboratory experiment and the mechanistic model estimates, while estimations from the regression method tended to exceed those from the other approaches. Storage capacity estimates ranged from 0·22 mm to 0·80 mm for pure oak zones, from 0·24 mm to 1·12 mm for mixed zones and from 0·53 mm to 1·17 mm for pure beech zones. The increase of storage capacity with increasing proportion of beech in the canopy resulted from higher beech LAI compared with oak. Similarly, for mixed and pure beech canopies, storage capacity was higher for high density zones than for low density zones as a result of the increase in LAI with increasing local basal area; in contrast, for pure oak, the storage capacity was not related to basal area because of the lower shade‐tolerance of this species compared with beech. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Changes in stream water quality due to logging of the boreal forest in the Montmorency Forest,Québec     

Yohann Tremblay  Alain N. Rousseau  André P. Plamondon  Denis Lévesque  Marcel Prévost 《水文研究》2009,23(5):764-776

Summer stream water quality was monitored before and following the logging of 50% of the boreal forest within three small watersheds (<50 ha) nested in the ‘Ruisseau des Eaux‐Volées’ Experimental Watershed, Montmorency Forest (Québec, Canada). Logging was conducted in winter, on snow cover according to recommended best management practices (BMPs) to minimize soil disturbance and protect advance growth. A 20‐m forest buffer was maintained along perennial streams. In watershed 7·2, cut‐blocks were located near the stream network and logging was partially allowed within the riparian buffer zone. In watersheds 7·5 and 7·7, logging occurred farther away from the stream network. Observations were also made for watershed 7·3 that collected the runoff from watersheds 7·2 and 7·5, and watershed 7·6, the uproad portion of watershed 7·7. The control watershed 0·2 was contiguous to the impacted watersheds and remained undisturbed. Following clearcutting, changes in summer daily maximum and minimum stream temperatures remained within ± 1 °C while changes in diurnal variation did not decrease by more than 0·5 °C. Concentrations of NO₃^? greatly increased by up to 6000% and concentrations of K⁺ increased by up to 300% during the second summer after logging. Smaller increases were observed for Fe_total (up to 71%), specific conductance (up to 26%), and Mg²⁺ (up to 19%). Post‐logging pH decreased slightly by no more than 7% while PO₄^3? concentration remained relatively constant. Suspended sediment concentrations appeared to increase during post‐logging, but there was not enough pre‐logging data to statistically confirm this result. Logging of moderate intensity and respecting established BMPs may account for the limited changes of water quality parameters and the low exceedances of the criteria for the protection of aquatic life. The proximity of the cutover to the stream network and logging within the riparian zone did not appear to affect water quality. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Low calcification rates and calcium carbonate production in Porites panamensis at its northernmost geographic distribution          下载免费PDF全文

Carlos Orión Norzagaray‐López  Luis Eduardo Calderon‐Aguilera  José Martín Hernández‐Ayón  Héctor Reyes‐Bonilla  Juan P. Carricart‐Ganivet  Rafael Andrés Cabral‐Tena  Eduardo Francisco Balart 《Marine Ecology》2015,36(4):1244-1255

Porites panamensis is a hermatypic coral present in the eastern Pacific Ocean. Skeletal growth parameters have been reported, but studies of the relationship between annual calcification rates and environmental controls are scarce. In this study, we investigated three aspects of the annual calcification rates of P. panamensis: growth parameters among three P. panamensis populations; the sea surface temperature as a calcification rate control spanning a latitudinal gradient; and calcium carbonate production among three sites. Growth parameters varied among the sites due to the colony growth form. Massive colonies in the north showed a higher calcification rate than encrusting colonies in the south (mean: 1.22–0.49 g CaCO₃ · cm^?2 · yr^?1), where variations in calcification rates were related to growth rate (0.91–0.38 cm · yr^?1) rather than to skeletal density differences (overall mean ± SD, 1.31 ± 0.04 g CaCO₃ · cm^?3). Our results showed a positive linear relationship between annual calcification rates and sea surface temperatures within these P. panamensis populations. Differences were related to distinct oceanographic environments (within and at the entrance of the Gulf of California) with different sea surface temperature regimes and other chemical properties. Different populations calcified under different environmental conditions. Calcium carbonate production was dependent upon the calcification rate and coral cover and so carbonate production was higher in the north (coral cover 12%) than in the south (coral cover 3.5). Thus, the studied sites showed low calcium carbonate production (0.25–0.43 kg CaCO₃ · m^?2 · yr^?1). Our results showed reduced calcification rates, regional temperature regime control over calcification rates, different growth forms, low coral cover and low calcium carbonate production rates in P. panamensis.  相似文献   

Isotropic and anisotropic pointing models     

András Pál  Krisztián Vida  László Mészáros  György Mező 《Experimental Astronomy》2016,41(1-2):1-15

This paper describes an alternative approach for generating pointing models for telescopes equipped with serial kinematics, esp. equatorial or alt-az mounts. Our model construction does not exploit any assumption for the underlying physical constraints of the mount, however, one can assign various effects to the respective components of the equations. In order to recover the pointing model parameters, classical linear least squares fitting procedures can be applied. This parameterization also lacks any kind of parametric singularity. We demonstrate the efficiency of this type of model on real measurements with meter-class telescopes where the results provide a root mean square accuracy of 1.5?2 arcseconds.  相似文献   

An inverse procedure to estimate transmissivity from heads and SP signals     

Straface S  Fallico C  Troisi S  Rizzo E  Revil A 《Ground water》2007,45(4):420-428

Experimental hydraulic heads and electrical (self-potential) signals associated with a pumping test were used in an inverse model to estimate the transmissivity distribution of a real aquifer. Several works reported in the literature show that there is a relatively good linear relationship between the hydraulic heads in the aquifer and electrical signals measured at the ground surface. In this experimental test field, first, the current coupling coefficient was determined by the best fit between experimental and modeled self-potential signals at the end of the pumping phase. Soon afterward, with the hydraulic heads obtained from the self-potential signals, the transmissivity distribution of the aquifer was conditioned by means an inverse model based on the successive linear estimator (SLE). To further substantiate the estimated T field from the SLE analysis, we analyzed the drawdown rate, the derivative of the drawdown with respect to the ln(t), because the drawdown rate is highly sensitive to the variability in the transmissivity field. In our opinion, these results show that self-potential signals allow the monitoring of subsurface flow in the course of pumping experiments, and that electrical potentials serve as a good complement to piezometric observations to condition and characterize the transmissivity distribution of an aquifer.  相似文献   

Molecular and isotopic partitioning of low-molecular-weight hydrocarbons during migration and gas hydrate precipitation in deposits of a high-flux seepage site     

Thomas Pape  André Bahr  Janet Rethemeyer  John D. Kessler  Heiko Sahling  Kai-Uwe Hinrichs  Stephan A. Klapp  William S. Reeburgh  Gerhard Bohrmann 《Chemical Geology》2010,269(3-4):350-363

Detailed knowledge of the extent of post-genetic modifications affecting shallow submarine hydrocarbons fueled from the deep subsurface is fundamental for evaluating source and reservoir properties. We investigated gases from a submarine high-flux seepage site in the anoxic Eastern Black Sea in order to elucidate molecular and isotopic alterations of low-molecular-weight hydrocarbons (LMWHC) associated with upward migration through the sediment and precipitation of shallow gas hydrates. For this, near-surface sediment pressure cores and free gas venting from the seafloor were collected using autoclave technology at the Batumi seep area at 845 m water depth within the gas hydrate stability zone.Vent gas, gas from pressure core degassing, and from hydrate dissociation were strongly dominated by methane (> 99.85 mol.% of ∑[C₁–C₄, CO₂]). Molecular ratios of LMWHC (C₁/[C₂ + C₃] > 1000) and stable isotopic compositions of methane (δ¹³C = ? 53.5‰ V-PDB; D/H around ? 175‰ SMOW) indicated predominant microbial methane formation. C₁/C₂₊ ratios and stable isotopic compositions of LMWHC distinguished three gas types prevailing in the seepage area. Vent gas discharged into bottom waters was depleted in methane by > 0.03 mol.% (∑[C₁–C₄, CO₂]) relative to the other gas types and the virtual lack of ¹⁴C–CH₄ indicated a negligible input of methane from degradation of fresh organic matter. Of all gas types analyzed, vent gas was least affected by molecular fractionation, thus, its origin from the deep subsurface rather than from decomposing hydrates in near-surface sediments is likely.As a result of the anaerobic oxidation of methane, LMWHC in pressure cores in top sediments included smaller methane fractions [0.03 mol.% ∑(C₁–C₄, CO₂)] than gas released from pressure cores of more deeply buried sediments, where the fraction of methane was maximal due to its preferential incorporation in hydrate lattices. No indications for stable carbon isotopic fractionations of methane during hydrate crystallization from vent gas were found. Enrichments of ¹⁴C–CH₄ (1.4 pMC) in short cores relative to lower abundances (max. 0.6 pMC) in gas from long cores and gas hydrates substantiates recent methanogenesis utilizing modern organic matter deposited in top sediments of this high-flux hydrocarbon seep area.  相似文献