Geomorphic-centered classification of wetlands on the Qinghai-Tibet Plateau, Western China   总被引：1，自引：1，他引：0  

GAO Jay  LI Xi-lai  Gary BRIERLEY  Alan CHEUNG  YANG Yuan-wu 《山地科学学报》2013,10(4):632-642

In this paper a geomorphic-centered system was proposed for classifying the wetlands on the Qinghai-Tibet Plateau in western China, where the flora comprises primarily grasses. Although the geomorphic properties (e.g., elevation and morphology) of wetlands form the primary criteria of classification, this system also takes hydrological processes into implicit consideration. It represents an improvement over the hydrogeomorphic perspective as the relative importance of the two components (wetness and landform) of wetlands is clearly differentiated. This geomorphic-centered perspective yields insights into the hydrogeomorphic dynamics of plateau wetlands while indicates their vulnerability to change and degradation indirectly. According to this geomorphic-centered perspective, all plateau wetlands fall into one of the seven types of alpine, piedmont, valley, terrace, floodplain, lacustrine, and riverine in three elevational categories of upland, midland, and lowland. Upland (alpine and piedmont) wetlands with the steepest topography are the most sensitive to change whereas midland (floodplain, terrace and valley) wetlands are less vulnerable to degradation owing to a high water reserve except terrace wetlands. They have a dry surface caused by infrequent hydrological replenishment owing to their higher elevation than the channel. Low lying (lacustrine and riverine) wetlands are the most resilient. The geomorphic-centered perspective developed in this paper provides a framework for improving recognition and management of wetlands on the Plateau. Resilient wetlands can be grazed more intensively without the risk of degradation. Fragile and vulnerable wetlands require careful managementto avoid degradation.  相似文献   

A semi-analytical solution based on a numerical solution of the solute transport of a conservative and nonreactive tracer     

Zhang J  Clare J  Guo J 《Ground water》2012,50(4):633-638

In the evaluation of potential risk from ingestion of groundwater near an impacted site, numerical simulation of fate and transport processes of chemicals of concern is often required. If there is potential concern about multiple chemicals, numerical simulation of each chemical separately is often needed. In this paper, a semi-analytical solution is presented based on a numerical solution of the transport of a conservative and nonreactive tracer. When multiple chemicals undergoing sorption and first-order degradation need to be modeled, we can avoid performing individual numerical simulations for each chemical by applying the semi-analytical solution. Numerical test runs were conducted to verify the semi-analytical solution; simulation results reveal that the concentrations derived from the semi-analytical solution are identical to those derived from the individual numerical fate and transport model simulations. The semi-analytical solution requires steady-state flow conditions, no continuing contaminant source, and similar initial source concentration distributions.  相似文献   

Optimizing spectral wave estimates with adjoint-based sensitivity maps     

Mark Orzech  Jay Veeramony  Stylianos Flampouris 《Ocean Dynamics》2014,64(4):487-505

A discrete numerical adjoint has recently been developed for the stochastic wave model SWAN. In the present study, this adjoint code is used to construct spectral sensitivity maps for two nearshore domains. The maps display the correlations of spectral energy levels throughout the domain with the observed energy levels at a selected location or region of interest (LOI/ROI), providing a full spectrum of values at all locations in the domain. We investigate the effectiveness of sensitivity maps based on significant wave height (H _s ) in determining alternate offshore instrument deployment sites when a chosen nearshore location or region is inaccessible. Wave and bathymetry datasets are employed from one shallower, small-scale domain (Duck, NC) and one deeper, larger-scale domain (San Diego, CA). The effects of seasonal changes in wave climate, errors in bathymetry, and multiple assimilation points on sensitivity map shapes and model performance are investigated. Model accuracy is evaluated by comparing spectral statistics as well as with an RMS skill score, which estimates a mean model–data error across all spectral bins. Results indicate that data assimilation from identified high-sensitivity alternate locations consistently improves model performance at nearshore LOIs, while assimilation from low-sensitivity locations results in lesser or no improvement. Use of sub-sampled or alongshore-averaged bathymetry has a domain-specific effect on model performance when assimilating from a high-sensitivity alternate location. When multiple alternate assimilation locations are used from areas of lower sensitivity, model performance may be worse than with a single, high-sensitivity assimilation point.  相似文献   

The case for establishing ecosystem-scale marine reserves     

Jay Nelson  Heather Bradner 《Marine pollution bulletin》2010,60(5):635-637

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A search at two eclipses for short-period waves that heat the corona     

Pasachoff  Jay M.  Babcock  Bryce A.  Russell  Kevin D.  McConnochie  Timothy H.  Diaz  J. Sebastian 《Solar physics》2000,195(2):281-298

As part of a study of the cause of solar coronal heating, we searched for high-frequency (1 Hz) intensity oscillations in coronal loops in the [Fexiv] coronal green line. We summarize results from observations made at the 3 November 1994, total solar eclipse from the International Astronomical Union site in Putre, Chile, through partly cloudy skies, and at the 26 February 1998 total solar eclipse from Nord, Aruba, through clear skies. We discuss the image reduction and analysis of two simultaneous series of coronal CCD images digitized at 10 Hz for a total time of 160 s in Chile. One series of images was taken through a filter isolating the 5303 Å[Fexiv] coronal green line and the other through a 100 Å filter in the nearby K-corona continuum. We then discuss the modifications made for the 1998 eclipse, and the image reduction and analysis for those image sequences. After standard calibrations and image alignment of both data sets, we use Fourier analysis to search in the [Fexiv] channel for intensity oscillations in loops at the base of the corona. Such oscillations in the 1-Hz range are predicted as a result of density fluctuations from the resonant absorption of MHD waves. The dissipation of a significant amount of mechanical energy from the photosphere into the corona through this mechanism could provide sufficient energy to heat the corona. At neither eclipse do we find evidence for oscillations in the [Fexiv] green line at a level greater than 2% of coronal intensity.  相似文献   

Volatile emission on the moon; Possible sources and release mechanisms     

Friesen  Larry Jay 《Earth, Moon, and Planets》1975,13(4):425-430

Evidence for very recent emission of volatiles on the Moon is primarily of four types: (1) transient lunar optical events observed by Earth-based astronomers; (2) excursions on Apollo SIDE and mass spectrometer instruments; (3) localized Rn²²²/Po²¹⁰ enhancements on the lunar surface detected by Apollo 15 and 16 orbital alpha spectrometers; (4) presence in lunar fines of retrapped Ar⁴⁰ and other volatiles. Available evidence indicates that the release rate of volatile substances into the lunar atmosphere is not steady, but instead sporadic and episodic. Rn²²²/Po²¹⁰ anomalies are at locations that are among those from which transient events have most often been reported (edges of maria, certain specific craters), and are probably related to them. Volatiles emitted at maria rims may originate in the Moon's fluid core, reaching the surface through deep cylindrical fault systems that ring the maria borders. The sources of volatiles emitted at craters such as Aristarchus or Tsiolkovsky, which possess floors which are cracked or filled with dark lava and possess central peaks, are more likely to be local pockets of magma or trapped gas at shallower depths. The volatiles are produced directly by radioactive decay (He⁴, Ar⁴⁰, Rn) and by heating (other volatiles). The release by heating can occur either during melting or by ‘bakeout’ of unmelted materials. Release of gas into the lunar atmosphere is probably triggered by buildup of its own pressure. This may be assisted by tidal forces exerted on the Moon by the Earth. In addition to independent release, volatile emission is also expected to accompany other lunar activity, such as ash flows, if any lunar volcanism is presently active.

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The rings of Uranus: Occultation profiles from three observatories     

J.L. Elliot  J.H. Elias  R.G. French  Jay A. Frogel  W. Liller  K. Matthews  K.J. Meech  D.J. Mink  P.D. Nicholson  B. Sicardy 《Icarus》1983,56(2):202-208

Occultation profiles for the nine confirmed Uranian rings obtained from Las Campanas, the European Southern Observatory, and Cerro Tololo on 15–16 August 1980 are compared. The α ring shows a “double-dip” structure; the η ring shows a broad and narrow component (similar to Saturn's F ring); and the ε ring shows six features that appear in the data from all three observatories. Diffraction fringes appear at the edges of several of the occultation profiles.  相似文献   

Minchinia nelsoni (MSX) infections in the James River seed-oyster area and their expulsion in spring     

Jay D. Andrews 《Estuarine, Coastal and Shelf Science》1983,16(3):255-269

Spread of a new oyster disease caused by Minchinia nelsoni (MSX) in lower Chesapeake Bay in 1959–1960 threatened Virginia's James River seed area. Infections appeared in the lower half of the seed area in 1960 and 1961, but few oysters died from the disease and infections were eliminated by oysters in April-May the following spring. Distribution of the disease in controlled broadly by low salinities that inhibit development of infections and allow oysters to discharge plasmodia. Penetrations of the seed area occurred in dry and wet years, but mortalities occurred only in 1964 and 1980, both years of low precipitation. Little mortality was caused by transplanting infected seed oysters to other rivers because only low-salinity grounds were planted after 1959–1960 when severe mortalities occurred in areas of high salinities. In most years, infections were minimal in the seed area and other estuaries where salinities do not exceed 15–20‰ in late summer and fall. Salinities <10‰ prevailed in most of the seed area when oysters expelled the pathogen in early spring.  相似文献   

Spectral observations of spicules at two heights in the solar chromosphere     

Jay M. Pasachoff  Robert W. Noyes  Jacques M. Beckers 《Solar physics》1968,5(2):131-158

An observational program at the Sacramento Peak Observatory in 1965 provided high-dispersion spectra of the solar chromosphere in several spectral regions simultaneously. These regions included various combinations of the spectral lines Hα, Hβ and H?, the D₃-line of Hei, the infrared triplet of Oi, and the H- and K-lines and the infrared triplet of Caii. With the use of an image slicer the observations were made simultaneously at two heights in the solar chromosphere separated by several thousand kilometers. From these data we draw the following conclusions:

1. Emission of different lines arises in the same chromospheric features. The intensity ratio of lines of different elements varies significantly from spicule to spicule. For the H- and K-lines of ionized calcium, this ratio remains constant, independent of wavelength throughout the line, overall intensity, and height in the chromosphere. Two rare-earth lines in the wing of the H-line show no spicular structure at all.
2. The line-of-sight velocities of many features reverse as a function of time, although most spicules show velocities in only one direction. The simultaneous spectra at two heights show most spicules to have the same line-of-sight velocity at both. There may be an additional class of features, mostly rapidly moving, whose members have line-of-sight velocities that increase with height. These features comprise perhaps 10% of the total. Velocity changes occur simultaneously, to within 20 sec, at two heights separated by 1800 km, indicating velocities of propagation of hundreds of km/sec. The velocity field of individual features is often quite complicated; many spectral features are inclined to the direction of dispersion, implying that differential mass motions are present.
3. The existence of anomalously broad H and K profiles is real. Even with high dispersion and the best seeing, such profiles are not resolved into smaller features. The central reversal in K, H and Hα appears to remain unshifted when the wings are displaced in wavelength, indicating that the reversal is non-spicular.

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The equation of state of Al,H-bearing SiO2 stishovite to 58 GPa     

Dmitry L. Lakshtanov  Carine B. Vanpeteghem  Jennifer M. Jackson  Jay D. Bass  Guoyin Shen  Vitali B. Prakapenka  Konstantin Litasov  Eiji Ohtani 《Physics and Chemistry of Minerals》2005,32(7):466-470

We have determined the P-V equation of state of Al-rich H-bearing SiO₂ stishovite by X-ray powder diffraction at pressures up to 58 GPa using synchrotron radiation. The sample contained 1.8 wt% Al₂O₃ and up to 500 ppm H₂O, and had a composition that would coexist with Mg-silicate perovskite in a subducted slab. By fitting a third-order Birch-Murnaghan equation of state to our compression data, we obtained a bulk modulus K _T0=298(7) GPa with K′=4.3(5). With K′ fixed to a value of 4, the bulk modulus K _T0=304(3) GPa. Our results indicate that Al³⁺ and H⁺ have a small effect on the elastic properties of stishovite. Compared with data obtained up to 43.8 GPa, peak intensities changed and we observed a decreased quality of fit to a tetragonal unit cell at pressures of 49 GPa and higher. These changes may be an indication that the rutile↔CaCl₂ transition occurs between these pressures. After laser annealing of the sample at 58.3(10) GPa and subsequent decompression to room conditions, the cell volume is the same as before compression, giving strong evidence that the composition of the recovered sample is also unchanged. This suggests that Al and H are retained in the sample under extreme P-T conditions and that stishovite can be an agent for transporting water to the deepest lower mantle.  相似文献