Competitive effects of fish in structurally simple habitats: perch,invertebrates, and goldeneye in small boreal lakes     

Petri?NummiEmail author  Veli-Matti?V??n?nen  Martti?Rask  Kari?Nyberg  Keijo?Taskinen 《Aquatic Sciences - Research Across Boundaries》2012,74(2):343-350

We determined the associations between Eurasian perch Perca fluviatilis, invertebrates, and common goldeneye Bucephala clangula in boreal lakes. Our aim was to test the hypothesis that perch play a controlling role in small, oligotrophic, acidic, and poorly vegetated boreal lakes, affecting both invertebrate numbers and community structure. In addition, we predicted that perch impact lake usage by goldeneye. In the observational part of our study, we first explored the association between perch, invertebrates and goldeneye (pairs and broods per shore km) in 18 boreal, poorly vegetated lakes. Perch densities were associated negatively with invertebrate abundance and lake usage by goldeneye broods. In the experimental part in three fish-free lakes, we found that upon successful perch introductions, the number and biomass of invertebrates, the proportion of large dytiscids, and lake usage by goldeneye broods significantly decreased. We conclude that perch apparently plays a key role as a predator of invertebrates in boreal lakes with few aquatic macrophytes. It is evident that perch can strongly affect their prey populations and communities, and this predation may have an indirect effect on species, e.g. goldeneye, that consume the same prey.  相似文献   

Constraints on the nature of the subvolcanic reservoir at South Sister volcano,Oregon from U-series dating combined with sub-crystal trace-element analysis of plagioclase and zircon     

Mark E. Stelten  Kari M. Cooper 《Earth and Planetary Science Letters》2012

We present sub-crystal-scale ²³⁸U–²³⁰Th zircon ages and ²³⁸U–²³⁰Th–²²⁶Ra plagioclase ages of bulk mineral separates from the Holocene (2.0–2.3 ka) eruptions of the Rock Mesa (RM) and Devil's Hills (DH) rhyolites at South Sister volcano, Oregon. We link these age data with sub-crystal trace-element analyses of zircon and plagioclase to provide insight into the subvolcanic system at South Sister, as an example of a small-volume continental arc volcano. Our results document the presence of coeval yet physically-distinct regions within the magma reservoir and constrain the timescales over which these heterogeneities existed. Zircons from the RM and DH dominantly record ages from 20 to 80 ka, with some grains recording ages > 350 ka, whereas plagioclase records ²³⁰Th–²²⁶Ra ages of 2.3–6.8 ka (RM) and 4.0–9.6 ka (DH-3) and a ²³⁸U–²³⁰Th age of 10 ± 34 ka (DH-3). We interpret zircons with ages < 350 ka as antecrysts inherited from a longer lived upper-crustal magma reservoir from which the rhyolites were generated, based on crystallization ages coeval with earlier periods of silicic volcanism at South Sister, the undersaturated nature of the RM and DH magmas with respect to zircon, and Ti-in-zircon temperatures consistent with low-temperature (< 815 °C) crystallization. In contrast, plagioclase ages are near the eruption age and dominantly preserve information about the recent (< 10 ka), higher-temperature evolution of the host magmas. Although zircon and plagioclase record different crystallization ages, each phase crystallized over the same time period in the RM compared to DH rhyolites. Linking these crystal age data with sub-crystal trace-element analyses demonstrates that zircon and plagioclase have distinct trace-element characteristics between eruptions, which require that the RM and DH crystals (and therefore magmas) were derived from distinct regions that had evolved independently for > 50 ka within a heterogeneous magmatic system and coexisted as physically-distinct, dominantly-liquid bodies prior to eruption. Thus, we favor a model where rhyolites are generated in independent batches by accumulation of evolved liquids in a heterogeneous, largely crystalline reservoir. Similarities in crystal age and chemical data to that at other young silicic systems (e.g., Mount St. Helens, Okataina Caldera Complex) suggest that this model may be more generally applicable to silicic magmas.  相似文献   

Comparative analysis of Venus and Mars magnetotails     

A. Fedorov  C. Ferrier  S. Barabash  C. Mazelle  H. Gunell  K. Brinkfeldt  A. Grigoriev  M. Yamauchi  W. Baumjohann  A.J. Coates  D.R. Linder  K.C. Hsieh  J.-J. Thocaven  H. Koskinen  T. Sales  P. Riihela  N. Krupp  J. Luhmann  S. Orsini  A. Mura  M. Maggi  P. Brandt  K. Szego  R.A. Frahm  J.R. Sharber  P. Bochsler 《Planetary and Space Science》2008,56(6):812-817

We have an unique opportunity to compare the magnetospheres of two non-magnetic planets as Mars and Venus with identical instrument sets Aspera-3 and Aspera-4 on board of the Mars Express and Venus Express missions. We have performed both statistical and case studies of properties of the magnetosheath ion flows and the flows of planetary ions behind both planets. We have shown that the general morphology of both magnetotails is generally identical. In both cases the energy of the light (H⁺) and the heavy (O⁺, etc.) ions decreases from the tail periphery (several keV) down to few eV in the tail center. At the same time the wake center of both planets is occupied by plasma sheet coincident with the current sheet of the tail. Both plasma sheets are filled by accelerated (500-1000 eV) heavy planetary ions. We report also the discovery of a new feature never observed before in the tails of non-magnetic planets: the plasma sheet is enveloped by consecutive layers of He⁺ and H⁺ with decreasing energies.  相似文献   

Dual sensor streamer technology used in Sleipner CO2 injection monitoring     

Anne‐Kari Furre  Ola Eiken 《Geophysical Prospecting》2014,62(5):1075-1088

CO₂ has been injected into the saline aquifer Utsira Fm at the Sleipner field since 1996. In order to monitor the movement of the CO₂ in the sub‐surface, the seventh seismic monitor survey was acquired in 2010, with dual sensor streamers which enabled optimal towing depths compared to previous surveys. We here report both on the time‐lapse observations and on the improved resolution compared to the conventional streamer surveys. This study shows that the CO₂ is still contained in the subsurface, with no indications of leakage. The time‐lapse repeatability of the dual sensor streamer data versus conventional data is sufficient for interpreting the time‐lapse effects of the CO₂ at Sleipner, and the higher resolution of the 2010 survey has enabled a refinement of the interpretation of nine CO₂ saturated layers with improved thickness estimates of the layers. In particular we have estimated the thickness of the uppermost CO₂ layer based on an analysis of amplitude strength together with time‐separation of top and base of this layer and found the maximum thickness to be 11 m. This refined interpretation gives a good base line for future time‐lapse surveys at the Sleipner CO₂ injection site.  相似文献   

A GIS-based method for the selection of the location of residence     

Xavier ALBACETE  Kari PASANEN  Mikko KOLEHMAINEN 《地球空间信息科学学报》2012,15(1)

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Theoretical interpretation of photometric properties of the Martian surface and atmosphere     

Kari Lumme  Leonard J. Martin  William A. Baum 《Icarus》1981,45(2):379-397

Earth-based UBV photometry, high-quality photographs from the Lowell Observatory collection, and Mariner 9 data have been combined with a new radiative transfer theory to derive physical parameters for the Martian surface and atmosphere, both before and during the 1971 dust storm. We find that the dust particles of the storm had a single-scattering albedo of 0.84 ± 0.02 and an asymmetry factor of 0.35 ± 0.10 in green (V) light. The geometric albedo of Mars was 0.15 and the phase integral 1.83, which yield 0.27 for the Bond albedo. The mean optical thickness of the “clear” atmosphere averaged over the whole planet was 0.15 ± 0.05 and was not detectably dependent on wavelength. Geometric albedos for the surface are 0.25 (light areas) and 0.17 (dark areas) in V, 0.095 in B (both areas), and 0.060 in U (both areas). The soil particles are moderately backward scattering with an asymmetry factor of ?0.20, indicating them to be rather opaque. The mean surface roughness, on a scale larger than that of individual dust particles and therefore large compared with the wavelength, is 0.57. This represents the depth/radius ratio of an average hole and it is only one-half as large as values typical for the Moon and asteroids.  相似文献   

线阵探测器(LDA)的现状及发展趋势   总被引：7，自引：1，他引：7  

J·柯斯克能  蔺春涛  高冬 《CT理论与应用研究》2002,11(3):12-15

本文概述了当前的线阵探测器(LDA)技术及未来发展，同时详细说明了LDA的重要性能特征，并对不同应用下不同的阵列设计进行了讨论。目前芬兰探测技术公司已将该项技术成功应用于大型集装箱检测系统，工业CT，医用CT，L型双能探测器等工业医学应用中．  相似文献   

Kinetic control of oxidation state at thermodynamically buffered potentials in subsurface waters     

John W. Washington  Dinku M. Endale  Kari E. Chappell 《Geochimica et cosmochimica acta》2004,68(23):4831-4842

Dissolved oxygen (DO) and organic carbon (C_org) are among the highest- and lowest-potential reactants, respectively, of redox couples in natural waters. When DO and C_org are present in subsurface settings, other couples are drawn toward potentials imposed by them, generating a bimodal clustering of calculated redox potentials. Which cluster a couple is drawn toward is determined by whether the couple’s oxidant or reductant is more concentrated. Generally, reactants >10^-6M are near equilibrium with their dominant complementary reactant and in a cluster, whereas reactants <10^-6M are relatively slow to react and diverge from the clusters. These observations suggest that reactions of higher-potential oxidants with lower-potential reductants commonly proceed simultaneously, regardless of the presence of other potential reactants, with the rates of reaction being determined more by concentration than relative potentials. As DO or C_org decreases, the potential gap separating couples diminishes. In waters having quantifiable concentrations of higher potential oxidants O₂ and NO₃^-, [H₂] was not diagnostic of their presence. In the water we analyzed having no quantifiable O₂ or NO₃^-, redox potential calculated with [H₂] was similar to potentials calculated for SO₄^2- reduction and methanogenesis. Composite reactions, NO₃^-→N₂ and O₂→H₂O, are best characterized in multiple steps due to slow reaction of low-concentration intermediates. The [CO] data we report, among the first for groundwater, are high compared to water equilibrated with the atmosphere.  相似文献   

Palaeomagnetic results from the Palaeozoic basement of the southern Drummond Basin, central Queensland, Australia   总被引：1，自引：0，他引：1  

Kari L. Anderson  Mark A. Lackie  David A. Clark 《Geophysical Journal International》2004,159(2):473-485

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First results from the plasma composition spectrometer PROMICS-3 in the Interball project     

I. Sandahl  S. Barabash  H. Borg  E. Yu. Budnik  E. M. Dubinin  U. Eklund  H. Johansson  H. Koskinen  K. Lundin  R. Lundin  A. Mostrom  R. Pellinen  N. F. Pissarenko  T. Pulkkinen  P. Toivanen  A. V. Zakharov 《Annales Geophysicae》1997,15(5):542-552

PROMICS-3 is a plasma experiment flown in the Russian project Interball. It performs three-dimensional (3D) measurements of ions in the energy range 4 eV–70 keV with mass separation and of electrons in the energy range 12 eV–35 keV. The Interball project consists of two main satellites, the Tail Probe and the Auroral Probe, each with one subsatellite. The Interball Tail Probe was launched on 3 August 1995, into a 65° inclination orbit with apogee at about 30 R_E. Both main satellites carry identical PROMICS-3 instruments and thus direct comparisons of the particle distributions will be possible once the Auroral Probe is launched. Furthermore, PROMICS-3-Tail is the first instrument measuring the 3D ion distribution function in the magnetospheric boundary layers at high latitudes. In this paper we describe the PROMICS-3 instrument and show initial results from the Tail probe, measurements of the mag-netosheath, plasma sheet, and ring current plasmas.  相似文献