Modelling hydrological connectivity of tropical floodplain wetlands via a combined natural and artificial stream network          下载免费PDF全文

Fazlul Karim  Anne Kinsey‐Henderson  Jim Wallace  Paul Godfrey  Angela H. Arthington  Richard G. Pearson 《水文研究》2014,28(23):5696-5710

The ecological condition and biodiversity values of floodplain wetlands are highly dependent on the hydrological connectivity of wetlands to adjacent rivers. This paper describes a method for quantifying connectivity between floodplain wetlands and the main rivers in a wet tropical catchment of northern Australia. We used a one‐dimensional hydrodynamic model to simulate time‐varying water depths across the stream network (i.e. rivers, streams and man‐made drains). The timing and duration of connectivity of seven wetlands (four natural and three artificial) with the two main rivers in the catchment were then calculated for different hydrological conditions. Location and areal extent of the wetlands and the stream network were identified using high‐resolution laser altimetry, and these data formed key inputs to the hydrodynamic model. The model was calibrated using measured water depths and discharges across the floodplain. An algorithm was developed to identify contiguous water bodies at daily time steps, and this gave the temporal history of connection and disconnection between wetlands and the rivers. Simulation results show that connectivity of individual wetlands to both rivers varies from 26 to 365 days during an average hydrological condition. Location, especially proximity to a main river, and wetland type (natural stream or artificial drain) were identified as key factors influencing these levels of connectivity. Some natural wetlands maintain connection with the river for most or all of the year, whereas the connectivity of some artificial wetlands varies from 26 to 36 days according to their patterns of network connection to adjacent rivers – a result that has important implications for the accessibility of these types of wetland to aquatic biota. Using readily available river gauge data, we also show how connectivity modelling can be used to identify periods when connectivity has fallen below critical thresholds for fish movement. These connectivity patterns within the floodplain network are central to the setting of river flows that will meet environmental requirements for biota that use floodplain wetlands during their life history. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Search for class II methanol masers at 23.1 GHz     

D. M. Cragg  A. M. Sobolev  J. L. Caswell  S. P. Ellingsen  P. D. Godfrey 《Monthly notices of the Royal Astronomical Society》2004,351(4):1327-1337

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Modelling methanol and hydroxyl masers in star-forming regions     

Dinah M.Cragg  rej M.Sobolev  Peter D.Godfrey 《Monthly notices of the Royal Astronomical Society》2002,331(2):521-536

Class II methanol masers are found in close association with OH main-line masers in many star-forming regions, where both are believed to flag the early stages in the evolution of a massive star. We have studied the formation of masers in methanol and OH under identical model conditions for the first time. Infrared pumping by radiation from warm dust at temperatures >100 K can account for the known maser lines in both molecules, many of which develop simultaneously under a range of conditions. The masers form most readily in cooler gas (<100 K) of moderately high density  (10⁵–10⁸ cm^-3)  , although higher gas temperatures and/or lower densities are also compatible with maser action. The agreement between the current model (developed for methanol) and the established OH maser trends is very encouraging, and we anticipate that further tuning of the model will further improve such agreement.
We find the gas-phase molecular abundance to be the key determinant of observable maser activity for both molecules. Sources exhibiting both 6668-MHz methanol and 1665-MHz OH masers have a typical flux density ratio of 16; our model suggests that this may be a consequence of maser saturation. We find that the 1665-MHz maser approaches the saturated limit for OH abundances >10^−7.3, while the 6668-MHz maser requires a greater methanol abundance >10⁻⁶. OH-favoured sources are likely to be less abundant in methanol, while methanol-favoured sources may be less abundant in OH or experiencing warm (>125 K), dense (∼10⁷ cm⁻³) conditions. These abundance requirements offer the possibility of tying the appearance of masers to the age of the new-born star via models of gas-phase chemical evolution following the evaporation of icy grain mantles.  相似文献   

Discovery of new 19.9-GHz methanol masers in star-forming regions     

S. P. Ellingsen  D. M. Cragg  J. E. J. Lovell  A. M. Sobolev  P. D. Ramsdale  P. D. Godfrey 《Monthly notices of the Royal Astronomical Society》2004,354(2):401-413

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The effect of crustal anisotropy on reflector depth and velocity determination from wide-angle seismic data: a synthetic example based on South Island, New Zealand     

N. J. Godfrey  N. I. Christensen  D. A. Okaya 《Tectonophysics》2002,355(1-4)

When deriving velocity models by forward modelling or inverting travel time arrivals from seismic refraction data, a heterogeneous but isotropic earth is usually assumed. In regions where the earth is not isotropic at the scale at which it is being sampled, the assumption of isotropy can lead to significant errors in the velocities determined for the crust and the depths calculated to reflecting boundaries. Laboratory velocity measurements on rocks collected from the Haast Schist terrane of South Island, New Zealand, show significant (up to 20%) compressional (P) wave velocity anisotropy. Field data collected parallel and perpendicular to the foliation of the Haast Schist exhibit as much as 11% P-wave velocity anisotropy. We demonstrate, using finite-difference full-wavefield modelling, the types of errors and problems that might be encountered if isotropic methods are used to create velocity models from data collected in anisotropic regions. These reflector depth errors could be as much as 10–15% for a 10-km thick layer with significant (20%) P-wave velocity anisotropy. The implications for South Island, New Zealand, where the problem is compounded by extreme orientations of highly anisotropic rocks (foliation which varies from horizontal to near vertical), are considered. Finally, we discuss how the presence of a significant subsurface anisotropic body might manifest itself in wide-angle reflection/refraction and passive seismic datasets, and suggest ways in which such datasets may be used to determine the presence and extent of such anisotropic bodies.  相似文献   

Tricarbon monoxide in TMC-1     

Brown RD  Godfrey PD  Cragg DM  Rice EH  Irvine WM  Friberg P  Suzuki H  Ohishi M  Kaifu N  Morimoto M 《The Astrophysical journal》1985,297(1):302-308

We report the measurement of three new lines of C3O in TMC-1. The observed peak antenna temperatures, appropriately corrected for atmospheric and telescope losses, are found to be consistent with a large velocity gradient radiative transfer model whose parameters span the range of standard values for this cloud. The derived fractional abundance for C3O is 1.4 x 10(-10), comparable with the results predicted from a model calculation based on a gas-phase ion-molecule reaction scheme. The results of negative searches for C3O in six other sources are not inconsistent with expected conditions in these clouds.  相似文献   

New interstellar masers in nonmetastable ammonia     

Madden SC  Irvine WM  Matthews HE  Brown RD  Godfrey PD 《The Astrophysical journal》1986,300(2):L79-L84

We report the astronomical detections of several ammonia inversion transitions involving nonmetastable levels with energies as high s 1090 K above the ground state. The (J, K) = (9, 6) inversion transition shows maser-like emission in the directions of W51, NGC 7538, W49, and DR 21(OH). The NH3 (6, 3) line exhibits similar characteristics in W51 but is seen in absorption in NGC 7538. These are the first definite detections of ammonia masers in space. The intensities and narrow line widths (0.5-1.5 km s-1) for the emission features are in contrast to the previously detected broad, weak, nonmetastable lines attributed to thermal emission in these sources. Temporal variability appears to be evident in the (9, 6) emission in W49 over a 4 month period. The highly excited (J, K) = (9, 6) and (6, 3) ammonia lines are found in regions containing compact H II regions and strong infrared sources with associated H2O and OH masers; i.e., in regions of active star formation.  相似文献   

Class II maser candidates in substituted methanol: CH₃OD, ¹³CH₃OH, CH₃¹⁸OH and CH₃SH     

K. P. Johns  D. M. Cragg  P. D. Godfrey  & A. M. Sobolev 《Monthly notices of the Royal Astronomical Society》1998,300(4):999-1005

We investigate the possibility of interstellar masers in transitions of the methanol isotopomers CH₃OD, ¹³CH₃OH and CH₃¹⁸OH, and of CH₃SH. The model used, in which masers are pumped through the first and second torsionally excited states by IR radiation, has accounted successfully for the Class II masers in main species methanol, ¹²CH₃¹⁶OH. Several potential maser candidates are identified for CH₃OD, their detectability depending on the enrichment of this species in star-forming regions. In ¹³CH₃OH and CH₃¹⁸OH the best maser candidates are direct counterparts of the well-known 6.7- and 12.2-GHz methanol masers, but the lower interstellar abundance of these substituted species means that the expected brightness is greatly reduced. The maser candidates in CH₃SH are also weak. By comparing these species we find that the large b -component of the dipole moment in methanol plays a significant role in its propensity to form masers, as does the strong torsion–rotation interaction due to the light hydroxyl frame. Thus the exceptional brightness of interstellar methanol masers is due to a favourable combination of molecular properties as well as high interstellar abundance.  相似文献   

Regulating public space on the beachfronts of Rio de Janeiro     

Godfrey BJ  Arguinzoni OM 《Geographical review》2012,102(1):17-34

Despite the fortification of buildings, streets, and public squares, Rio de Janeiro's beaches remain widely regarded as democratic spaces of social diversity and accessibility. Our study revisits the question of Rio's “democratic” beachfronts, based on local interviews, field observations, official reports, and newspaper accounts. We focus on historical and contemporary perceptions of planning, privatization, and public-order programs on the city's southern seaside. Institutional discourses have justified increasing regulation to combat threats of disorder and insecurity. While residents value the relative openness of beachfronts, they also acknowledge issues of safety, social segmentation, and subtle forms of bias. The public generally applauds recent “Shock of Order” policing and commercial revitalization, although critics lament the loss of traditional freedoms for informal beach vendors and casual sports. These paradoxes highlight enduring tensions between social order and hierarchy on one hand, and democratic rights and equality on the other.  相似文献   

Landscape analysis: Theoretical considerations and practical needs     

Andrew E. Godfrey  Emery T. Cleaves 《Environmental Geology》1991,17(2):141-155

Numerous systems of land classification have been proposed. Most have led directly to or have been driven by an author's philosophy of earth-forming processes. However, the practical need of classifying land for planning and management purposes requires that a system lead to predictions of the results of management activities.We propose a landscape classification system composed of 11 units, from realm (a continental mass) to feature (a splash impression). The classification concerns physical aspects rather than economic or social factors; and aims to merge land inventory with dynamic processes.Landscape units are organized using a hierarchical system so that information may be assembled and communicated at different levels of scale and abstraction. Our classification uses a geomorphic systems approach that emphasizes the geologic-geomorphic attributes of the units.Realm, major division, province, and section are formulated by subdividing large units into smaller ones. For the larger units we have followed Fenneman's delineations, which are well established in the North American literature. Areas and districts are aggregated into regions and regions into sections. Units smaller than areas have, in practice, been subdivided into zones and smaller units if required.We developed the theoretical framework embodied in this classification from practical applications aimed at land use planning and land management in Maryland (eastern Piedmont Province near Baltimore) and Utah (eastern Uinta Mountains).  相似文献