The Bear Brook Watershed in Maine: Multi-decadal whole-watershed experimental acidification     

Kaizad F. Patel  Ivan J. Fernandez  Sarah J. Nelson  Stephen A. Norton  Cheryl J. Spencer 《水文研究》2021,35(5):e14147

The Bear Brook Watershed in Maine (BBWM) is a long-term research site established to study the response of forest ecosystem function to environmental disturbances of chronic acidic deposition and ecosystem nitrogen enrichment. Starting in 1989, the West Bear (treated) watershed received bimonthly applications of ammonium sulfate [(NH₄)₂SO₄] fertilizer from above the canopy, whereas East Bear (reference) received ambient deposition. The treatments were stopped in 2016, marking the beginning of the recovery phase. Research at the site has focused on soils, streams, and vegetation. Here, we describe data collected over three decades at the BBWM—input and stream output nutrient fluxes, quantitative soil pits and soil chemistry, and soil temperature and moisture.  相似文献   

High energy phenomena in eta carinae     

Roberto F. Viotti  Lucio Angelo Antonelli  Sonja Rebecchi  Corinne Rossi 《Journal of Astrophysics and Astronomy》2002,23(1-2):19-22

We have investigated with BeppoSAX the long term behaviour of the harder X-ray component of the supposed supermassive binary system η Car along its 5.52 year cycle. We have found that in March 1998 during egress from the last December 1997 eclipse, this component was the same as outside eclipse, but for a large (×3.5) increase of NH _h , that can be attributed to the presence or formation of opaque matter in front of the source near periastron. Unexpectedly, at that time the iron 6.7 keV emission line was 40% stronger. BeppoSAX has for the first time found ahard X-ray tail extending to at least 50 keV, that cannot be adequately fitted with an additional hotter thermal component. The 2–100 keV spectrum of η Car is instead well fitted with an absorbed powerlaw spectrum with photon index 2.53, suggesting non-thermal emission as an alternative model for the core source.  相似文献   

NORTHERN AND SOUTHERN HEMISPHERIC POLAR LOWS——A COMPARATIVE STUDY          下载免费PDF全文

Erik A.Rasmussen 《Acta Meteorologica Sinica》1993,(3)

Northern Hemispheric“polar lows”,i.e.maritime,small,but fairly intense cyclonic systems have been studied formore than two decades.Recently researchers have turned their attention towards the occurrence of polar lows and othersmall-scale cyclonic disturbances on the Southern Hemisphere.In this paper a short account of our present knowledgeof Northern Hemispheric polar lows will be given,followed by some preliminary results of an investigation of the natureand occurrence of polar lows on the Southern Hemisphere.  相似文献   

Modelling the effect of low soil temperatures on transpiration by Scots pine     

Per‐Erik Mellander  Manfred Sthli  David Gustafsson  Kevin Bishop 《水文研究》2006,20(9):1929-1944

For ecosystem modelling of the Boreal forest it is important to include processes associated with low soil temperature during spring‐early summer, as these affect the tree water uptake. The COUP model, a physically based SVAT model, was tested with 2 years of soil and snow physical measurements and sap flow measurements in a 70‐year‐old Scots pine stand in the boreal zone of northern Sweden. During the first year the extent and duration of soil frost was manipulated in the field. The model was successful in reproducing the timing of the soil warming after the snowmelt and frost thaw. A delayed soil warming, into the growing season, severely reduced the transpiration. We demonstrated the potential for considerable overestimation of transpiration by the model if the reduction of the trees' capacity to transpire due to low soil temperatures is not taken into account. We also demonstrated that the accumulated effect of aboveground conditions could be included when simulating the relationship between soil temperature and tree water uptake. This improved the estimated transpiration for the control plot and when soil warming was delayed into the growing season. The study illustrates the need of including antecedent conditions on root growth in the model in order to catch these effects on transpiration. The COUP model is a promising tool for predicting transpiration in high‐latitude stands. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Propagation of the cosmic-ray iron group at intermediate energies     

C. Baixeras  M. Casas  F. Fernandez  A. Vidal-Quadras  M. Ortega 《Astrophysics and Space Science》1983,96(2):321-331

Elemental abundances of the VH group of cosmic radiation have been measured in the energy interval 250–550 MeV nucl^–1 in a balloon exposure at Sioux Falls (South Dakota) of a plastic detector LeXAN stack. The so obtained abundances have been extrapolated to the sources in the frame of the homogeneous model correcting for energy loss. After taking into account solar modulation, the best fit to model values has led to a escape mean free path _e = 5E ^–0.4 g cm^–2, whereE is the energy in GeV nucl^–1, forE>1 GeV nucl^–1, and a constant _e = 5 g cm^–2 forE1 GeV nucl^–1. When turning to the diffusion model, also including an energy loss term, a diffusion coefficientD=3×10²⁸ cm² s^–1 has been estimated.  相似文献   

Local kinematics of OB stars     

G. A. Pellegatti Franco 《Astrophysics and Space Science》1983,96(1):195-203

Analysis of observational data of OB stars show an, excellent agreement of the density distributions in space ?(x, y, z) as well as in velocity space \(\rho (\dot x,\dot y,\dot z)\) with the predictions of the density wave theory, the values for the density and velocity fluctuations are explained only by the non-linear theory. These theoretical calculations predict perturbations greater than ±10 km s^?1, consistent with the observations for the velocity field. Thus one should disregard analytical treatments of the linearized equations since they predict maximum perturbations of ±5km s^?1. Another consequence of this is the fact that the Gould's Belt is not a local anomaly, but a local feature of the density waves. The analysis of observational data show that the wave pattern is similar to that of the gas and dust.  相似文献   

Microbial mineralization and assimilation of black carbon: Dependency on degree of thermal alteration   总被引：4，自引：0，他引：4  

Sander Bruun  Erik S. Jensen  Lars S. Jensen 《Organic Geochemistry》2008,39(7):839-845

Black carbon is degraded slowly in the environment and its formation can therefore be an effective sink for atmospheric CO₂. This study examined whether charcoal is assimilated by microorganisms or not and estimated the rate of mineralization depending on the degree of thermal alteration of the black carbon. Charcoals were produced at three different temperatures from homogeneously ¹⁴C labelled plant material and incubated in soil, and ¹⁴C in the evolved CO₂ and the microbial biomass was measured. Unlike parallel plant samples, CO₂ evolution from the charcoals showed no lag phase, but a period of faster CO₂ evolution for the first 5–8 days followed by a period of slow evolution. The mineralization of charcoal appeared to decrease with increasing temperature at which it was produced. This was also the case after the initial period of fast CO₂ evolution. With the techniques used, it was not possible to observe any microbial assimilation of charcoal, either because it did not occur, or because the methods used were not sufficiently sensitive. However, the lack of a lag phase in the CO₂ evolution from the charcoals is in line with earlier evidence that charcoal is initially oxidized at the surfaces by abiotic processes.  相似文献   

Hydrogeochemical investigations and groundwater provinces of the Friuli Venezia Giulia Plain aquifers,northeastern Italy   总被引：2，自引：0，他引：2  

Franco Cucchi  Giuliana Franceschini  Luca Zini 《Environmental Geology》2008,55(5):985-999

Water resources are a key factor, particularly for the planning of the sustainable regional development of agriculture, as well as for socio-economic development in general. A hydrochemical investigation was conducted in the Friuli Venezia Giulia aquifer systems to identify groundwater evolution, recharge and extent of pollution. Temperature, pH, electric conductivity, total dissolved solids, alkalinity, total hardness, SAR, Ca²⁺, Na⁺, K⁺, Mg²⁺, Cl⁻, SO₄ ²⁻, NO₃ ⁻, HCO₃ ⁻ _, water quality and type, saturation indexes and the environmental stable isotope δ¹⁸O were determined in 149 sampling stations. The pattern of geochemical and oxygen stable isotope variations suggests that the sub-surface groundwater (from phreatic and shallow confined aquifers) is being recharged by modern precipitations and local river infiltrations. Four hydrogeological provinces have been recognised and mapped in the Friuli Venezia Giulia Plain having similar geochemical signatures. These provinces have different degrees of vulnerability to contamination. The deep confined groundwater samples are significantly less impacted by surface activities; and it appears that these important water resources have very low recharge rates and would, therefore, be severely impacted by overabstraction.  相似文献   

A model for the viscosity of rhyolite as a function of H₂O-content and pressure: A calibration based on centrifuge piston cylinder experiments     

Paola Ardia  Daniele Giordano 《Geochimica et cosmochimica acta》2008,72(24):6103-6123

The Newtonian viscosity of synthetic rhyolitic liquids with 0.15-5.24 wt% dissolved water was determined in the interval between 580 and 1640 °C and pressures of 1 atm and 5-25 kbar. Measurements were performed by combining static and accelerated (up to 1000g) falling sphere experiments on water-bearing samples, with high temperature concentric cylinder experiments on 0.15 wt% H₂O melts. These methods allowed viscosity determinations between 10² and 10⁷ Pa s, and cover the complete range of naturally occurring magmatic temperatures, pressures, and H₂O-contents for rhyolites.Our viscosity data, combined with those from previous studies, were modeled by an expression based on the empirical Vogel-Fulcher-Tammann equation, which describes viscosities and derivative properties (glass transition temperature T_g, fragility m, and activation volume of viscous flow Va) of silicic liquids as a function of P-T-X_(H2O). The fitted expressions do not account for composition-dependent parameters other than X_(H2O) and reproduce the entire viscosity database for silicic liquids to within 3.0% average relative error on log η (i.e. std. error of estimate of 0.26 log units).The results yield the expected strong decrease of viscosity with temperature and water content, but show variable pressure dependencies. Viscosity results to be strongly affected by pressure at low pressures; an effect amplified at low temperatures and water contents. Fragility, as a measure for the deviation from Arrhenian behavior, decreases with H₂O-content but is insensitive to pressure. Activation volumes are always largely negative (e.g., less than −10 cm³/mol) and increase strongly with H₂O-content. Variations in melt structure that may account for the observed property variations are discussed.  相似文献   

Effect of major anions on arsenate desorption from ferrihydrite-bearing natural samples     

Franco Frau  Riccardo BiddauLuca Fanfani 《Applied Geochemistry》2008

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