Rates, patterns, and impacts ofPhragmites australis expansion and effects of experimentalPhragmites control on vegetation, macroinvertebrates, and fish within tidelands of the lower Connecticut River     

R. Scott Warren  Paul E. Fell  Jonna L. Grimsby  Erika L. Buck  G. Chris Rilling  Rachel A. Fertik 《Estuaries and Coasts》2001,24(1):90-107

Phragmites expansion rates (linear at 1–3% yr⁻¹) and impacts of this expansion on high marsh macroinvertebrates, aboveground production, and litter decomposition fromPhragmites and other marsh graminoids were studied along a polyhaline to oligohaline gradient. These parameters, and fish use of creeks and high marsh, were also studied inPhragmites control sites (herbicide, mowing, and combined herbicide/mow treatments).Phragmites clones established without obvious site preferences on oligohaline marshes, expanding radially. At higher salinities,Phragmites preferentially colonized creekbank levees and disturbed upland borders, then expanded into the central marsh. Hydroperiods, but not salinities or water table, distinguishedPhragmites-dominated transects. Pooled samples ofPhragmites leaves, stems, and flowers decompose more slowly than other marsh angiosperms;Phragmites leaves alone decompose as or more rapidly than those of cattail. AbovegroundPhragmites production was 1,300 to 2,400 g m⁻² (about 23% of this as leaves), versus 600–800 g m⁻² for polyhaline to mesohaline meadow and 1,300 g m⁻² for oligohaline cattail-sedge marsh. Macroinvertebrates appear largely unaffected byPhragmites expansion or control efforts; distribution and densities are unrelated to elevation or hydroperiod, but densities are positively related to litter cover. Dominant fish captured leaving flooded marsh wereFundulus heteroclitus andAnguilla rostrata; both preyed heavily on marsh macroinvertebrates.A. rostrata andMorone americana tended to be more common inPhragmites, but otherwise there were no major differences in use patterns betweenPhragmites and brackish meadow vegetation. SAV and macroalgal cover were markedly lower within aPhragmites-dominated creek versus one withSpartina-dominated banks. The same fish species assemblage was trapped in both plus a third within the herbicide/mow treatment. Fish biomass was greatest from theSpartina creek and lowest from thePhragmites creek, reflecting abundances ofF. heteroclitus. Mowing depressedPhragmites aboveground production and increased stem density, but was ineffective for control.Phragmites, Spartina patens, andJuncus gerardii frequencies after herbicide-only treatment were 0.53-0.21; total live cover was <8% with a heavy litter and dense standing dead stems. After two growing seasonsAgrostis stolonifera/S. patens/J. gerardii brackish meadow characterized most of the herbicide/mow treatment area;Phragmites frequency here was 0.53, contributing 3% cover. Both values more than doubled after four years; a single treatment is ineffective for long-termPhragmites control.  相似文献   

Vertical seismic profile at Pike's Peak, Saskatchewan, Canada: turning rays and velocity anisotropy     

Rachel T. Newrick  Don C. Lawton 《Journal of Applied Geophysics》2003,54(3-4):401

First-arrival traveltimes from a multi-offset vertical seismic profile (VSP) were used to estimate velocity anisotropy in the presence of a vertical velocity gradient. A numerical model consisting of two layers with vertical velocity gradients of 3.1 and 1.2 s⁻¹, respectively, and global anisotropy parameters of =0.12±0.02 and δ=0.30±0.06 yielded first-arrival traveltimes that matched the observed traveltimes well. Shallow receivers were found to be crucial for constraining the vertical velocity field and for determining the parameters of anisotropy at depth.  相似文献   

Transnational Migration and the Gender Politics of Scale: Indonesian Domestic Workers in Saudi Arabia     

Rachel Silvey 《Singapore journal of tropical geography》2004,25(2):141-155

Recent research has begun to explore the dynamics of transnational migration from a feminist perspective, and studies of migrant domestic workers have played a prominent role in pushing forward this work. Emerging simultaneously, but largely separately, are explicit debates within geography about the politics of scale, the social construction of scale, and the gender dimensions of scale. This article develops an analysis of the gender politics of the production of scale, specifically, the ‘transnationalisation’ of Indonesian activist approaches to overseas migrant domestic workers' issues. Based on fieldwork in an Indonesian community in West Java that has recently become a sending area for migrants to Saudi Arabia and interviews with activists representing Indonesian migrant women, the article examines the various gender‐specific ways in which migrant women's rights activists construct and deploy the scales of the body, the nation and the transnational. It argues that activist approaches to migrant domestic workers' rights and the ways in which activists mobilise migrant women's narratives represent sophisticated feminist theoretical approaches to scale. By identifying and exploring the scale theory embedded in activist strategies, the analysis highlights the imbrication of feminist theory with practice, and underscores activists' agency in producing the meanings of specific scales. In so doing, the article is aimed more broadly at elaborating the ambivalent relationship between feminist activism/theory and transnationalism.  相似文献   

A model study of ATMOS observations and the heterogeneous loss of N2O5 by the sulphate aerosol layer     

Ralf Toumi  Slimane Bekki  Rachel Cox 《Journal of Atmospheric Chemistry》1993,16(2):135-144

The heterogeneous removal of N₂O₅ by sulphuric acid aerosols as been invoked to explain the decline of mid-latitude ozone in the last decade. We have used a photochemical model to study measurements of odd-nitrogen made by Spacelab 3. The gas-phase photochemical model overestimates the amount of N₂O₅ present. The loss of N₂O₅ by aerosols does reduce N₂O₅, but is likely to be slower than assumed in WMO (1992). The sunset measurements at 25.5 km cannot be explained by heterogeneous loss of N₂O₅ and is more likely to be due to a faster photolysis than assumed. New absorption cross-sections of HNO₃ reduce the photolysis of HNO₃ so that the model with gas-phase chemistry only gives better agreement at 19 km, than a model including heterogeneous chemistry.  相似文献   

Is there more to life? Relationalities in here and out there: a reply to Horton and Kraftl     

Peter Hopkins  Rachel Pain 《Area》2008,40(2):289-292

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Fish bile as a biomarker for metal exposure     

Hauser-Davis RA  Bastos FF  de Oliveira TF  Ziolli RL  de Campos RC 《Marine pollution bulletin》2012,64(8):1589-1595

Fish accumulate several trace elements in muscle, gills and liver, however studies also indicate that metals can be excreted through bile. Since metal contamination leads to modifications in bile composition, biliary excretion offers an alternative way to evaluate the presence of trace-elements. Bile is easier to obtain than other organs and presents a simpler matrix, making it easier for chemical pre-treatment. To verify if bile can be useful as a biomonitoring tool for metal contamination, liver and bile trace element concentrations were determined and correlated. The Artificial Neural Networks statistical technique was used to verify if liver trace-element quantification could be substituted by bile analysis. Results show that significant correlations were obtained between trace elements in bile and liver and the ANN validated the hypothesis that certain trace-elements in bile could be utilized instead of liver trace-elements. Further studies in this field are of interest to further validate this biomarker.  相似文献   

Surge in sulphur and halogen degassing from Ambrym volcano,Vanuatu     

Philipson Bani  Clive Oppenheimer  Vitchko I. Tsanev  Simon A. Carn  Shane J. Cronin  Rachel Crimp  Julie A. Calkins  Douglas Charley  Michel Lardy  Tjarda R. Roberts 《Bulletin of Volcanology》2009,71(10):1159-1168

Volcanoes provide important contributions to atmospheric budgets of SO₂ and reactive halogens, which play significant roles in atmospheric oxidative capacity and radiation. However, the global source strengths of volcanic emissions remain poorly constrained. These uncertainties are highlighted here by the first measurements of gas emission rates from Ambrym volcano, Vanuatu. Our initial airborne ultraviolet spectroscopic measurements made in January 2005 indicate fluxes of 18–270 kg s^-1 of SO₂, and 62–110 g s^-1 of BrO, into the atmosphere, placing Ambrym amongst the largest known contemporary point sources of both these species on Earth. We also estimate high Cl and F fluxes of ~8–14 and ~27–50 kg s^-1, respectively, for this period. Further observations using both airborne and spaceborne remote sensing reveal a fluctuating SO₂ output between 2004 and 2008, with a surge in the first half of 2005, and underline the substantial contribution that a single passively degassing volcano can make to the atmospheric budget of sulfur and halogens.  相似文献   

Quantitative analysis of net-transgressive shoreline trajectories and stratigraphic architectures: mid-to-late Jurassic of the North Sea rift basin     

Gary J. Hampson  Peter J. Sixsmith  Rachel L. Kieft  Christopher A. -L. Jackson  Howard D. Johnson 《Basin Research》2009,21(5):528-558

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How to plant a merger tree     

Rachel S. Somerville  Tsafrir S. Kolatt 《Monthly notices of the Royal Astronomical Society》1999,305(1):1-14

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Reclassification of four aubrites as enstatite chondrite impact melts: Potential geochemical analogs for Mercury     

Arya Udry  Zoë E. Wilbur  Rachel R. Rahib  Francis M. McCubbin  Kathleen E. Vander Kaaden  Timothy J. McCoy  Karen Ziegler  Juliane Gross  Christopher DeFelice  Logan Combs  Brent D. Turrin 《Meteoritics & planetary science》2019,54(4):785-810

We present petrologic and isotopic data on Northwest Africa (NWA) 4799, NWA 7809, NWA 7214, and NWA 11071 meteorites, which were previously classified as aubrites. These four meteorites contain between 31 and 56 vol% of equigranular, nearly endmember enstatite, Fe,Ni metal, plagioclase, terrestrial alteration products, and sulfides, such as troilite, niningerite, daubréelite, oldhamite, and caswellsilverite. The equigranular texture of the enstatite and the presence of the metal surrounding enstatite indicate that these rocks were not formed through igneous processes like the aubrites, but rather by impact processes. In addition, the presence of pre‐terrestrially weathered metal (7.1–14 vol%), undifferentiated modal abundances compared to enstatite chondrites, presence of graphite, absence of diopside and forsterite, low Ti in troilite, and high Si in Fe,Ni metals suggest that these rocks formed through impact melting on chondritic and not aubritic parent bodies. Formation of these meteorites on a parent body with similar properties to the EHa enstatite chondrite parent body is suggested by their mineralogy. These parent bodies have undergone impact events from at least 4.5 Ga (NWA 11071) until at least 4.2 Ga (NWA 4799) according to ³⁹Ar‐⁴⁰Ar ages, indicating that this region of the solar system was heavily bombarded early in its history. By comparing NWA enstatite chondrite impact melts to Mercury, we infer that they represent imperfect petrological analogs to this planet given their high metal abundances, but they could represent important geochemical analogs for the behavior and geochemical affinities of elements on Mercury. Furthermore, the enstatite chondrite impact melts represent an important petrological analog for understanding high‐temperature processes and impact processes on Mercury, due to their similar mineralogies, Fe‐metal‐rich and FeO‐poor silicate abundances, and low oxygen fugacity.  相似文献