High-frequency monitoring of hydrological and biogeochemical fluxes in forested catchments of southern Chile     

Cristián Frêne  Juan J. Armesto  Freddy Véliz  Fernando D. Alfaro  Kathleen C. Weathers 《水文研究》2021,35(5):e14175

The variability of rainfall-dependent streamflow at catchment scale modulates many ecosystem processes in wet temperate forests. Runoff in small mountain catchments is characterized by a quick response to rainfall pulses which affects biogeochemical fluxes to all downstream systems. In wet-temperate climates, water erosion is the most important natural factor driving downstream soil and nutrient losses from upland ecosystems. Most hydrochemical studies have focused on water flux measurements at hourly scales, along with weekly or monthly samples for water chemistry. Here, we assessed how water and element flows from broad-leaved, evergreen forested catchments in southwestern South America, are influenced by different successional stages, quantifying runoff, sediment transport and nutrient fluxes during hourly rainfall events of different intensities. Hydrograph comparisons among different successional stages indicated that forested catchments differed in their responses to high intensity rainfall, with greater runoff in areas covered by secondary forests (SF), compared to old-growth forest cover (OG) and dense scrub vegetation (CH). Further, throughfall water was greatly nutrient enriched for all forest types. Suspended sediment loads varied between successional stages. SF catchments exported 455 kg of sediments per ha, followed by OG with 91 kg/ha and CH with 14 kg/ha, corresponding to 11 rainfall events measured from December 2013 to April 2014. Total nitrogen (TN) and phosphorus (TP) concentrations in stream water also varied with rainfall intensity. In seven rainfall events sampled during the study period, CH catchments exported less nutrients (46 kg/ha TN and 7 kg/ha TP) than SF catchments (718 kg/ha TN and 107 kg/ha TP), while OG catchments exported intermediate sediment loads (201 kg/ha TN and 23 kg/ha TP). Further, we found significant effects of successional stage attributes (vegetation structure and soil physical properties) and catchment morphometry on runoff and sediment concentrations, and greater nutrients retention in OG and CH catchments. We conclude that in these southern hemisphere, broad-leaved evergreen temperate forests, hydrological processes are driven by multiple interacting phenomena, including climate, vegetation, soils, topography, and disturbance history.  相似文献   

The standard theory of extinction and the spectrum of stars with very little reddening     

Frdric Zagury 《New Astronomy》2001,6(8):345-486

This paper examines the relationship between spectra of stars of same spectral type with extremely low reddenings. According to the standard theory, the relationship between the spectrum of stars with same spectral type and small, but different reddenings should be different in the optical and in the UV. This difference is not observed: the ratio of the spectra of two stars in directions where the reddening is large enough to be detected and low enough not to give a noticeable 2200 Å bump is an exponential of 1/λ from the near-infrared to the far-UV. This result is in conformity with the ideas introduced in preceding papers: the exponential optical extinction extends to the UV, and the spectrum of stars with enough reddening is contaminated by light scattered at close angular distance from the stars. An application will be the determination of the spectrum of a non-reddened star from the spectrum of a star of same spectral type with little reddening.  相似文献   

Impact of the seasonal variations of composition on the temperature field of Titan’s stratosphere     

Sébastien Lebonnois  Frédéric Hourdin  David Luz 《Icarus》2003,163(1):164-174

We investigate the role of seasonal variations of Titan’s stratospheric composition on the temperature. We use a general circulation model coupled with idealized chemical tracers that reproduce variations of ethane (C₂H₆), acetylene (C₂H₂), and hydrogen cyanide (HCN). Enhancement of the mole fractions of these compounds, at high latitudes in the winter hemisphere relative to their equatorial values, induces a relative decrease in temperature above approximately 0.2 mbar, with a peak amplitude around −20 K, and a relative increase in temperature below, around 1 mbar, with a peak amplitude around +7 K. These thermal effects are mainly due to the variations of the cooling to space induced by the varying distributions. The ethane, acetylene, and hydrogen cyanide variations affect the cooling rates in a similar way, with the dominant effect being due to ethane, though its latitudinal variations are small.  相似文献   

The physics of pulses in gamma-ray bursts: emission processes, temporal profiles and time-lags     

Frédéric Daigne  Robert Mochkovitch 《Monthly notices of the Royal Astronomical Society》2003,342(2):587-592

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Diffuse Galactic light at high Galactic latitude: nature and interpretation     

Frédéric Zagury 《Monthly notices of the Royal Astronomical Society》2006,370(4):1763-1770

The hypothesis of an extended red emission (ERE) in diffuse Galactic light (DGL) has been put forward in 1998 by Gordon, Witt & Friedmann who found that scattered starlight was not enough to explain the amount of DGL in the R band, in some high Galactic latitude directions. This paper re-investigates, for high Galactic latitudes, the brightnesses and colours of DGL, integrated star and galaxy light (ISGL), and of the total extrasolar light (ISGL+DGL) measured by Pioneer. Under the traditional assumption that DGL is forward scattering of background starlight by interstellar dust on the line of sight, ISGL and Pioneer have very close colours, as it is found by Gordon, Witt & Friedmann. Pioneer observations at high |b| thus accept an alternative and simple interpretation, with no involvement of ERE in DGL.  相似文献   

Transfer factors of contamination between the German Bight and its tributary waters derived from measured tritium and Cs-137 activity concentrations     

Christoph Wedekind  Günter Främcke 《Ocean Dynamics》1991,44(2):59-75

Summary Evaluation of the results of radioactivity monitoring in the southern North Sea between 1977 and 1987 has shown that in the water of the German Bight three areas stand out due to their different ratios between salinity and concentration of dissolved Cs-137 and tritium. While salinity steadily increases with greater distance from the coast, the Cs-137 concentration above 34 PSU (Practical Salinity Unit) increases sharply and shows how far water from the western and central North Sea, contaminated by nuclear reprocessing in Sellafield (Irish Sea), reaches into the German Bight. In the 34 to 32.5 PSU range, the influence can be seen of water contaminated by tritium originating in the rivers Rhein, Maas and Schelde, precipitation and the nuclear reprocessing plant at La Hague (Channel). Below 32.5 PSU, the influence of the influx from the rivers Elbe, Weser and Ems becomes apparent. These rivers are less contaminated with tritium.Assuming that Cs-137 and tritium, like the salinity of sea water, behave conservatively and that the decay-time of these two isotopes is long compared with the time-scale of water exchange in the southern North Sea, the concentration values measured are used to calculate the structure of the water masses in the three areas of the German Bight mentioned above using the mixing principle. Evaporation is taken into account. Results show that beyond 34 PSU, about half the sea water originates in the western central North Sea while the other half comes from the Channel. Below 34 PSU, the first mentioned share amounts only to a few per cent. Results also show that fresh water from the Rhein delta and precipitation, increasing with a decrease in salinity from 34 to 32.5 PSU, accounts for a maximum of 5% each. The fresh water influx into the German Bight via the rivers Elbe, Weser and Ems amounts to app. 11% when the PSU value reaches 29. The calculated portions are the mean values for the observation period. The number of measurements available makes it impossible to distinguish more exactly between the temporal and spatial variability of the amounts of the individual components.The quantity of each calculated portion of sea water also represents the transfer factor of concentration between the nuclide concentration in the source (e. g. the Rhein) and the concentration in the German Bight. In addition, these factors are used to calculate the transfer factors of discharge using the annual drainage rates of the sources. Thus a radioactive discharge rate of 10¹⁵ Bq per year into the Rhein would produce a mean activity concentration of 0.34 Bq/l in the German Bight (at a salinity of 33.5 PSU). To verify the calculated transfer factors, tritium concentrations in the German Bight are derived from existing environmental tritium data and the results are compared with the values actually measured.

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Transferkaktoren zwischen der Deutschen Bucht und ihren Zuflüssen abgeleitet aus der Tritium- und Cs-137-Aktivitätskonzentration in den beteiligten Gewässern

Zusammenfassung Eine zusammenhängende Auswertung der Meßergebnisse der Radioaktivitätsüberwachung in der südlichen Nordsee über den Zeitraum 1977 bis 1987 hat gezeigt, daß im Wasser der Deutschen Bucht deutlich drei durch den Salzgehalt des Meerwassers und die Konzentration der gelösten Radionuklide charakterisierte Bereiche zu unterscheiden sind.Während der Salzgehalt mit wachsender Entfernung von der Küste stetig zunimmt, steigt die Cs-137-Konzentration oberhalb 34 PSU (Practical Salinity Unit) sprunghaft an und signalisiert die Grenze, bis zu der das durch die Kernbrennstoff-Wiederaufarbeitung in Sellafield (Irische See) kontaminierte Meerwasser der westlichen und mittleren Nordsee in die Deutsche Bucht vordringt. Im Bereich 34 bis 32,5 PSU ist das von Westen zugeführte, stärker Tritium-kontaminierte Wasser aus Rhein, Maas, Schelde und atmosphärischem Niederschlag zu erkennen, an das sich unterhalb 32,5 PSU der geringer mit Tritum kontaminierte Zufluß aus Elbe, Weser und Ems anschließt.Davon ausgehend, daß sich Cs-137 und Tritium wie der Salzgehalt im Meerwasser konservativ verhalten und daß weiterhin die Halbwertzeit des radioaktiven Zerfalls dieser beiden Nuklide lang ist gegenüber den Wasseraustauschzeiten im betrachteten Meeresgebiet, wurden die in der südlichen Nordsee gemessenen sowie aus der Literatur für den Süßwasserbereich entnommenen Konzentrationswerte dazu genutzt, um rechnerisch mit Hilfe des Mischungsgesetzes den Wassermassenaufbau in den drei genannten Salinitätsbereichen in der Deutschen Bucht quantitativ zu bestimmen. Es zeigte sich, daß oberhalb von 34 PSU das Meerwasser aus etwa gleichen Teilen aus der westlichen/mittleren Nordsee und dem Kanal stammt, während unterhalb dieser Salzgehaltsgrenze nur noch mit wenigen Prozentanteilen Wasser aus der mittleren Nordsee zu finden ist. Ferner ergab sich, daß das aus dem Rheinmündungsbiet bzw, aus dem atmosphärischen Niederschlag stammende Süßwasser — mit sinkendem Salzgehalt steigend — bei 32,5 PSU einen maximalen Anteil von jeweils 5% an Meerwasser hat. Der direkte Süßwasserzufluß aus Elbe, Weser und Ems beträgt in die Deutsche Bucht bei 29 PSU ca. 11%.Die berechneten Anteile sind Mittelwerte über den gesamten Beobachtungszeitraum; die Anzahl der Messungen läßt eine genauere Unterscheidung in zeitliche und räumliche Variabilität der Zusammensetzung nicht zu.Die Größe des jeweils bestimmten Anteils am Meerwasser stellt gleichzeitig den Transferfaktor der Konzentration zwischen der Nuklidkonzentration im Ursprungsgewässer (z. B. dem Rhein) und der sich daraus einstellenden Konzentration in der Deutschen Bucht dar. Ferner wurden die Transferfaktoren der Konzentration in Verbindung mit aus der Literatur entnommenen Größen der jährlichen Abflußmengen der Ursprungsgewässer genutzt, um auch die Transferfaktoren der jährlichen Einbringung zu ermitteln. So ergibt die jährliche Einbringung von 10¹⁵ Bq eines Nuklides z. B. in den Rhein bei 33,5 PSU in der Deutschen Bucht eine mittlere Konzentration von 0,34 Bq/l.Als Anwendungsbeispiel und zur Überprüfung der Richtigkeit der Transferfaktoren wird die Auswertung des Tritiumauslasses bei La Hague auf die Deutsche Bucht berechnet und mit den gemessenen Werten verglichen.

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The relationship between hydrodynamic properties and weathering of soils derived from volcanic rocks,Galapagos Islands (Ecuador)     

M. Adelinet  J. Fortin  N. d’Ozouville  S. Violette 《Environmental Geology》2008,56(1):45-58

The aim of this interdisciplinary study is to examine a component of the hydrological cycle in Galapagos by characterizing soil properties. Nine soil profiles were sampled on two islands. Their physical and hydrodynamic properties were analyzed, along with their mineralogical composition. Two groups of soils were identified, with major differences between them. The first group consists of soils located in the highlands (>350 m a.s.l.), characterized by low hydraulic conductivity (<10⁻⁵ m s⁻¹) and low porosity (<25%). These soils are thick (several meters) and homogeneous without coarse components. Their clay fraction is considerable and dominated by gibbsite. The second group includes soils located in the low parts of the islands (<300 m a.s.l.). These soils are characterized by high hydraulic conductivity (>10⁻³ m s⁻¹) and high porosity (>35%). The structure of these soils is heterogeneous and includes coarse materials. The physical properties of the soils are in good agreement with the variations of the rainfall according to the elevation, which appears as the main factor controlling the soil development. The clayey alteration products constrain soils physical and hydrodynamic properties by reducing the porosity and consequently the permeability and also by increasing water retention.  相似文献   

Formation of Zn–Ca phyllomanganate nanoparticles in grass roots     

Bruno Lanson  Matthew A. Marcus  Sirine Fakra  Frdric Panfili  Nicolas Geoffroy  Alain Manceau 《Geochimica et cosmochimica acta》2008,72(10):2478-2490

It is now well established that a number of terrestrial and aquatic microorganisms have the capacity to oxidize and precipitate Mn as phyllomanganate. However, this biomineralization has never been shown to occur in plant tissues, nor has the structure of a natural Mn(IV) biooxide been characterized in detail. We show that the graminaceous plant Festuca rubra (red fescue) produces a Zn-rich phyllomanganate with constant Zn:Mn and Ca:Mn atomic ratios (0.46 and 0.38, respectively) when grown on a contaminated sediment. This new phase is so far the Zn-richest manganate known to form in nature (chalcophanite has a Zn:Mn ratio of 0.33) and has no synthetic equivalent. Visual examination of root fragments under a microscope shows black precipitates about ten to several tens of microns in size, and their imaging with backscattered and secondary electrons demonstrates that they are located in the root epidermis. In situ measurements by Mn and Zn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and X-ray diffraction (XRD) with a micro-focused beam can be quantitatively described by a single-phase model consisting of Mn(IV) octahedral layers with 22% vacant sites capped with tetrahedral and octahedral Zn in proportions of 3:1. The layer charge deficit is also partly balanced by interlayer Mn and Ca. Diffracting crystallites have a domain radius of 33 Å in the ab plane and contain only 1.2 layers (8.6 Å) on average. Since this biogenic Mn oxide consists mostly of isolated layers, basal 00l reflections are essentially absent despite its lamellar structure. Individual Mn layers are probably held together in the Mn–Zn precipitates by stabilizing organic molecules. Zinc biomineralization by plants likely is a defense mechanism against toxicity induced by excess concentrations of this metal in the rhizosphere.  相似文献   

Budgets of Mn,Cd and Cu in the macrotidal Gironde estuary (SW France)     

Stéphane Audry  Gérard BlancJörg Schäfer  Frédéric GuérinMatthieu Masson  Sébastien Robert 《Marine Chemistry》2007

The behavior and budget of Mn, Cd and Cu in the Gironde estuary were investigated through data from both the water column (WC) and sediment depth profiles. In the estuarine freshwater reaches, Mn and Cd removal from and Cu addition to the dissolved phase occurs with a magnitude equivalent to 10%, 30% and 25% of their respective annual fluvial gross dissolved input, respectively. In the saline estuary, diffusive benthic outflow is the main source of dissolved Mn (74% of the total gross dissolved input within the estuary) to the WC. In contrast, Cd (96%) and Cu (89%) are mainly released into the dissolved phase of the WC from fluvial, estuarine and dredging-related particles through complexation (Cd) and organic carbon mineralization (Cu). Anthropogenic activities (sediment dredging) induce pore water inputs, particulate sulfide oxidation and sediment resuspension, significantly contributing to the metal budget of the WC. The related amounts of metals released could be equivalent to 20–50% (Cd) and up to 70% (Cu) of their respective net dissolved addition. Mass balances suggest that a large part of the metals previously released into the dissolved phase from processes within the estuary are removed by suspended particles due to (co-)precipitation of Fe/Mn (oxy)hydroxides and scavenging on autochthonous organic matter. On an annual basis, the Gironde estuary acts as a net sink of dissolved Mn, removing 60% of the dissolved fluvial inputs, and as a net source of dissolved Cd and Cu, contributing ∼ 85% and 20–45% to the dissolved Cd and Cu fluxes to the ocean.  相似文献   

The European coastal zone: characterization and first assessment of ecosystem metabolism     

Frdric Gazeau  Stephen V. Smith  Bernard Gentili  Michel Frankignoulle  Jean-Pierre Gattuso 《Estuarine, Coastal and Shelf Science》2004,60(4):673-694

The geomorphic, oceanographic, terrestrial and anthropogenic attributes of the European coastal zone are described and published data on ecosystem function (primary production and respiration) are reviewed. Four regions are considered: the Baltic Sea, Mediterranean Sea, Black Sea and the European Atlantic coast including the North Sea. The metabolic database (194 papers) suffers from a non-homogeneous geographical coverage with no usable data for the Black Sea which was therefore excluded from this part of our study. Pelagic gross primary production in European open shelves is, by far, the most documented parameter with an estimated mean of 41 mmol C m⁻² d⁻¹, the lowest value is reported in the Mediterranean Sea (21 mmol C m⁻² d⁻¹) and the highest one in the Atlantic/North Sea area (51 mmol C m⁻² d⁻¹). Microphytobenthic primary production, mostly measured in shallow areas, is extrapolated to the entire 0–200 m depth range. Its contribution to total primary production is low in all regions (mean: 1.5 mmol C m⁻² d⁻¹). Although macrophyte beds are very productive, a regional production estimate is not provided in this study because their geographical distribution along the European coastline remains unknown. Measurements of pelagic community respiration are clearly too sparse, especially below the euphotic zone, to yield an accurate picture of the fate of organic matter produced in the water column. With a mean value of 17 mmol C m⁻² d⁻¹, benthic community respiration consumes approximately 40% of the pelagic organic matter production. Estuaries generally exhibit high metabolic rates and a large range of variation in all parameters, except microphytobenthic primary production. Finally, the problem of eutrophication in Europe is discussed and the metabolic data obtained in the framework of the Land–Ocean Interactions in the Coastal Zone (LOICZ) project are compared with available direct measurements of net ecosystem production.  相似文献