Variations in the depth distribution of phosphorus in soil profiles and implications for model-based catchment-scale predictions of phosphorus delivery to surface waters     

P.N. Owens  L.K. Deeks  G.A. Wood  M.J. Betson  E.I. Lord  P.S. Davison 《Journal of Hydrology》2008,350(3-4):317-328

The PSYCHIC process-based model for predicting sediment and phosphorus (P) transfer within catchments uses spatial data on soil-P derived from the National Soil Inventory (NSI) data set. These soil-P values are based on bulked 0–15 cm depth and do not account for variations in soil-P with depth. We describe the depth distribution of soil-P (total and Olsen) in grassland and arable soils for the dominant soil types in the two PSYCHIC study catchments: the Avon and the Wye, UK. There were clear variations in soil-P (particularly Olsen-P) concentrations with depth in untilled grassland soils while concentrations of total-P were broadly constant within the plough layer of arable soils. Concentrations of Olsen-P in arable soils, however, exhibited maximum values near the soil surface reflecting surface applications of fertilisers and manures between consecutive ploughing events. When the soil-P concentrations for the surface soil (0–5 cm average) were compared to both the profile-averaged (0–15 cm) and the NSI (0–15 cm) values, those for the surface soil were considerably greater than those for the average 0–15 cm depth. Modelled estimates of P loss using the depth-weighted average soil-P concentrations for the 0–5 cm depth layer were up to 14% greater than those based on the NSI data set due to the preferential accumulation of P at the soil surface. These findings have important implications for the use of soil-P data (and other data) in models to predict P losses from land to water and the interpretation of these predictions for river basin management.  相似文献   

Detection Of Soft X-Ray Emission From Comet C/1995 O1 (Hale–Bopp)     

Owens  Alan  Oosterbroek  T.  Orr  A.  Parmar  A. N.  Schulz  R.  Tozzi  G.P. 《Earth, Moon, and Planets》1997,77(3):293-298

We report the detection of soft X-rays from comet C/1995 O1 (Hale-Bopp) by the Low Energy Concentrator Spectrometer (LECS) on-board the X-ray satellite, BeppoSAX. The observations took place on 1996 September 10–11 approximately 1 day after a large dust outburst (Schulz et al., 1997–1999). After correcting for the comets motion, a 7σ enhancement was found centered (2.1 ± 1.3) x 10⁵ km from the position of the nucleus, in the general solar direction. The total X-ray luminosity in the 0.1–2.0 keV energy band is 5 x 10¹⁶ erg s⁻¹ which is at least a factor of ∼ 3 greater than measured by the Extreme Ultraviolet Explorer (EUVE)4 days later and suggests that the bulk of the emission measured by the LECS is related to the dust outburst. The extracted LECS spectrum is well fit by a thermal bremsstrahlung-like distribution of temperature of 0.29 ± 0.06 keV - consistent with that observed in other comets. We find no evidence for fluorescent carbon or oxygen emission and place 95% confidence limits of 1.0 x 10¹⁵ and 7.8 x 10¹⁵ erg s⁻¹ to narrow line emission at 0.28 and 0.53 keV, respectively. We calculate that if such lines are present, they constitute at most 18% of the 0.1–2.0 keV continuum luminosity. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Deriving the GRB distance scale     

Alan Owens  S. Sembay  Bradley E. Schaefer 《Astrophysics and Space Science》1995,231(1-2):449-452

We describe a method to address the burster origin problem by determining their distance scale. We show that this can be easily carried out at soft X-ray wavelengths by measuring the effective column densities of a representative sample of burst spectra. We demonstrate the effectiveness of the technique by simulating the performance of a small CATSAT-type mission (Forrestet al., 1995).  相似文献   

First results from the TGRS high-resolution GRB Spectrometer     

D. M. Palmer  B. J. Teegarden  H. Seifert  N. Gehrels  T. L. Cline  R. Ramaty  A. Owens  K. Hurley  N. Madden  R. Pehl 《Astrophysics and Space Science》1995,231(1-2):161-164

The Transient Gamma Ray Spectrometer (TGRS) is a 215 cm³ passivelycooled germanium detector designed primarily to study spectral features of gamma ray bursts. Since shortly after its launch on 1994 Nov. 1 it has been producing high-resolution spectra of GRBs and solar flares. Some of these spectra are presented here.Although it has not yet detected any line features in GRBs-none were expected so early in the mission-several bursts have been seen simultaneously by TGRS, the Konus instruments on the same spacecraft, and the BATSE instrument on Compton GRO. A comparison of the spectra obtained by these various instruments, as presented here, may resolve the question of whether line features actually exist, and if so provide detailed spectroscopy to determine their physical origin.  相似文献   

A set modified equinoctial orbit elements     

M. J. H. Walker  B. Ireland  Joyce Owens 《Celestial Mechanics and Dynamical Astronomy》1985,36(4):409-419

Modified equinoctial elements are introduced which are suitable for perturbation analysis of all kinds of orbit. Equations of motion in Lagrangian and Gaussian forms are derived. Identities connecting the partial derivatives of the disturbing function with respect to equinoctial elements are established. Numerical comparisons of the evolution of a perturbed, highly eccentric, elliptic orbit analysed in equinoctial elements and by Cowell's method show satisfactory agreement.  相似文献   

The calculation of a best-fit ellipsoid from elliptical sections on arbitrarily orientated planes     

W.H. Owens 《Journal of Structural Geology》1984,6(5):571-578

A two-stage procedure is described for the calculation of a best-fit ellipsoid from elliptical sections measured on three or more arbitrary planes. The first stage produces an initial, trial solution. This is used as a starting point for a standard, linear, least-squares treatment to determine the best-fit ellipsoid.Factors influencing the reliability of a solution (for example, number of measurements and quality of data) are discussed in the context of real and synthetic examples. The examples indicate that the procedure described is relatively robust and they allow guidelines for its routine practical application to be suggested.  相似文献   

Comparison of crustal velocity profiles determined by seismic refraction and teleseismic methods     

G. Zandt  T.J. Owens 《Tectonophysics》1986,128(1-2)

Recently, two diverse seismic techniques were applied independently to the study of the crustal structure of the Cumberland Plateau, eastern Tennessee. One involved a reinterpretation of a refraction experiment performed in 1965 by the U.S. Geological Survey, consisting of two 400 km long, reversed refraction lines. The other entailed the inversion of broadband teleseismic P waveforms recorded at a single three-component broadband station, RSCP, located at the intersection of the two refraction profiles. A comparison of the two sets of velocity profiles revealed many similarities and some significant differences. Both sets of velocity models consist of three major crustal layers: (1) an upper crust (V_p = 6.1–6.4 km/s) down to about 17 km, (2) a mid-crust (V_p = 6.7–6.9 km/s) between 17 and 40 km depth, (3) a lower crust (V_p = 7.2–7.4 km/s) from 40 to 51 km depth. The refraction models have linear transition zones up to 11 km thick at the base of each layer, whereas the teleseismic models have more irregular transition zones at the base of the mid- and lower crust. The differences in the results of these studies are attributed to the differing frequency bandwidths of the data sets; the predominant sensitivity of the teleseismic data to shear velocities, compared to compressional velocities for the refraction data; and the different analysis procedures involved in each method. Nevertheless, the similarities indicate that the teleseismic waveform method with broadband data is capable of retreiving comparable crustal information as the Cumberland Plateau refraction survey. In addition, it provides the kind of complementary information required to constrain the composition of the continental lower crust and uppermost mantle.  相似文献   

Magnetic susceptibility anisotropy,strain, and progressive deformation in Permian sediments from the Maritime Alps (France)     

Roy Kligfield  W.H. Owens  W. Lowrie 《Earth and Planetary Science Letters》1981,55(1):181-189

The relationships among magnetic susceptibility anisotropy, finite strain, and progressive deformation have been studied in Permian red shales and slates of the Maritime Alps (southeastern France). These rocks contain deformed reduction spots which serve as finite strain indicators. The magnetic fabric of undeformed regions is modified during deformation to yield characteristic magnetic susceptibility anisotropy patterns and a magnetic equivalent of the deformation path derived from strain measurements. The magnetic fabric changes progressively from oblate to prolate, and back to oblate as deformation increases. The quantitative relationships between natural strain and magnetic anisotropy in these rocks have been determined. They differ between the less and more deformed areas, perhaps due to a change in deformation mechanism accompanying an increase in metamorphism. The relationships provide a rapid means of strain determination using magnetic measurements but their variation emphasizes the need for local structural control.  相似文献   

A simple model for non-vanishing rotational hysteresis in haematite     

W.H. Owens 《Physics of the Earth and Planetary Interiors》1981,27(2):106-113

The model, applicable to fine-grained haematite, assumes that the magnetization of a grain is constrained to lie in the basal plane, within which there is a single easy axis. Following Stoner and Wohlfarth (1948), torque curves and rotational hysteresis are calculated, for various field strengths, as a function of the orientations of the basal plane and easy axis. The results show that, for certain orientations, rotational hysteresis may be expected to persist to very high field strengths. Further, the dependence of rotational hysteresis on orientation implies that rotational hysteresis is anisotropic and thus, that, for a distribution of grains, the anisotropy of resultant rotational hysteresis will reflect the degree of preferred orientation. It may therefore serve as a rock fabric parameter. Calculated models of resultant rotational hysteresis for assumed preferred orientation distributions compare favourably with measurements on a sample of Cambrian purple slate from North Wales.  相似文献   

Sedimentation in arctic proglacial lakes: Mittivakkat Glacier,south‐east Greenland     

Bent Hasholt  Desmond E. Walling  Philip N. Owens 《水文研究》2000,14(4):679-699

Several sediment cores were collected from two proglacial lakes in the vicinity of Mittivakkat Glacier, south‐east Greenland, in order to determine sedimentation rates, estimate sediment yields and identify the dominant sources of the lacustrine sediment. The presence of varves in the ice‐dammed Icefall Lake enabled sedimentation rates to be estimated using a combination of X‐ray photography and down‐core variations in ¹³⁷Cs activity. Sedimentation rates for individual cores ranged between 0·52 and 1·06 g cm⁻² year⁻¹, and the average sedimentation rate was estimated to be 0·79 g cm⁻² year⁻¹. Despite considerable down‐core variability in annual sedimentation rates, there is no significant trend over the period 1970 to 1994. After correcting for autochthonous organic matter content and trap efficiency, the mean fine‐grained minerogenic sediment yield from the 3·8 km² basin contributing to the lake was estimated to be 327 t km⁻² year⁻¹. Cores were also collected from the topset beds of two small deltas in Icefall Lake. The deposition of coarse‐grained sediment on the delta surface was estimated to total in excess of 15 cm over the last c. 40 years. In the larger Lake Kuutuaq, which is located about 5 km from the glacier front and for which the glacier represents a smaller proportion of the contributing catchment, sedimentation rates determined for six cores collected from the centre of the lake, based on their ¹³⁷Cs depth profiles, were estimated to range between 0·05 and 0·11 g cm⁻² year⁻¹, and the average was 0·08 g cm⁻² year⁻¹. The longer‐term (c. 100–150 years) average sedimentation rate for one of the cores, estimated from its unsupported ²¹⁰Pb profile, was 0·10–0·13 g cm⁻² year⁻¹, suggesting that sedimentation rates in this lake have been essentially constant over the last c. 100–150 years. The average fine‐grained sediment yield from the 32·4 km² catchment contributing to the lake was estimated to be 13 t km⁻² year⁻¹. The ¹³⁷Cs depth profiles for cores collected from the topset beds of the delta of Lake Kuutuaq indicate that in excess of 27 cm of coarse‐grained sediment had accumulated on the delta surface over the last approximately 40 years. Caesium‐137 concentrations associated with the most recently deposited (uppermost) fine‐grained sediment in both Icefall Lake and Lake Kuutuaq were similar to those measured in fine‐grained sediment collected from steep slopes in the immediate proglacial zone, suggesting that this material, rather than contemporary glacial debris, is the most likely source of the sediment deposited in the lakes. This finding is confirmed by the ¹³⁷Cs concentrations associated with suspended sediment collected from the Mittivakkat stream, which are very similar to those for proglacial material. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献