A COMPARISON OF HYDROLOGY AND VEGETATION BETWEEN A CHANNELIZED STREAM AND A NONCHANNELIZED STREAM IN WESTERN TENNESSEE     

Scott B. Franklin  Reza S. Pezeshki  Tanya L. Scheff  John A. Kupfer  Ryan A. Hanson  Randall W. Gentry 《自然地理学》2013,34(3):254-274

The purpose of this study was to provide baseline data on floodplain forest structure, composition, and function that would be needed to predict and monitor the consequences of a proposed stream restoration project. This project would involve the “dechannelization” of Stokes Creek, a stream in western Tennessee that was channelized and leveed in the first half of the 1900s. To this end, we collected data on surface hydrology, soil redox potential (Eh), and the structure and composition of the floodplain vegetation of Stokes Creek. To place our findings into a regional context, we also collected comparable vegetation data from plots located along a nonchannelized stream reach of the Wolf River near Moscow, Tennessee. While hydrologic fluctuations of floodplain sites were synchronous with river dynamics for the Wolf River, the hydrology of floodplain sites at Stokes Creek was constrained by the influence of beaver dams, backflooding, and ponding of overland flow behind levees. Consequently, composition of the forest overstory, understory, and herbaceous strata was significantly different between the two sites. For example, Stokes Creek had a noticeable lack of cypress and tupelo sites, and a greater abundance of red maple. Analyses of size-class structure and woody debris quantity reinforced the existing differences between the more natural and human-impacted systems. While the current hydrology apparently has a negative affect on bottomland hardwoods, scattered regeneration stems and soil redox measurements indicate that a dechannelization effort that yielded lower water tables in the Stokes Creek floodplain potentially could increase bottomland hardwood establishment. [Key words: channelization, western Tennessee, bottomland hardwoods, hydrology.]  相似文献   

Canary in a coal mine: perceptions of climate change risks and response options among Canadian mine operations     

James D. Ford  Tristan Pearce  Jason Prno  Frank Duerden  Lea Berrang Ford  Tanya R. Smith  Maude Beaumier 《Climatic change》2011,109(3-4):399-415

A survey documenting how climate change is perceived and responded to by Canadian mine operations was administered to a random sample of practitioners working at mine sites across Canada. Key findings include: (1) Mines are sensitive to climatic hazards; (2) There is concern about climate change among mine practitioners, but the majority have not yet noticed climate change to be affecting operations; (3) Future climate change is expected to have negative impacts for mine operations; (4) Mines are responding to climate change mainly through efforts to reduce greenhouse gas emissions but also through adaptation, although to a lesser degree; and (5) Knowledge of future climate change projections and impacts is limited, potentially constraining understanding of the nature of climate change risks. The survey compliments previous work documenting perceptions among upper level management on climate change in the Canadian mining industry. The results from both surveys are largely consistent, establishing that the mining sector perceives climate change as an emerging risk and is developing response options, but needs to invest more time and resources for adaptation to what are inevitable changes in climate. The results support the need for targeted in-depth research to assess the vulnerability of mining to climate change and to evaluate response options.  相似文献   

Evolution of Icelandic central volcanoes: evidence from the Austurhorn intrusion,southeastern Iceland     

Tanya Furman  Peter S Meyer  Fred Frey 《Bulletin of Volcanology》1992,55(1-2):45-62

The Austurhorn intrusive complex in southeastern Iceland represents an exhumed Tertiary central volcano. The geometry of the intrusion and geochemistry of the mafic and felsic rocks indicate Austurhorn was a volcanic center analogous to Eyjafjallajökull and Torfajökull in Iceland's eastern neovolcanic zone (EVZ). Early transitional tholeiitic basalt magmatism at Austurhorn formed a shallow crustal chamber 5 km in diameter. Apparent rhythmic modal layering of, and intrusive contacts within, the gabbro indicate the mafic chamber was replenished frequently as it cooled and crystallized. Felsic activity postdated near-solidification of the gabbro; numerous granitic magmas intruded along gabbro margins and within the adjacent crust. Field relations indicate that infrequent felsic replenishment prevented convective mixing of the Austurhorn chamber during this time, although commingled mafic and felsic magmas are observed in an extensive net veined complex. Late stage mafic dikes intrude the entire complex, suggesting that magmatic heat was abundantly available throughout the evolution of the Austurhorn system. Plagioclase and clinopyroxene compositions in mafic through felsic rocks, including gabbros, support a model of progressive differentiation. Field relations constrain the felsic magmas to originate at P1 kbar, presumably by fractional crystallization. The structure and geochemistry of the Austurhorn intrusive complex suggest formation in an immature rift environment similar to the modern EVZ. The proposed rift segment was parallel to the western and eastern neovolcanic zones, and probably resulted from a reorganization of plate boundaries 7 Ma (Saemundsson 1979; Helgason 1985; Jancin et al. 1985) triggered by activity of the Iceland mantle plume.  相似文献   

Fine scale mapping of fractional tree canopy cover to support river basin management     

Sicong Gao  Pascal Castellazzi  R. Willem Vervoort  Tanya M. Doody 《水文研究》2021,35(4):e14156

Management of water, regionally, nationally and globally will continue to be a priority and complex undertaking. In riverine systems, biotic components like flora and fauna play critical roles in filtering water so it is available for human use and consumption. Preservation of ecosystems and associated ecosystem functions is therefore vital. In highly regulated large river basins, natural ecosystems are often supported through provision of environmental flows. Flow delivery, however, should be underpinned by rigorous monitoring to identify and prioritise biotic water requirements. Currently, large-scale monitoring solutions are scaled from remote sensing data via measurement of field evapotranspiration for woody tree vegetation species. However, as there is generally a mismatch between field data collection area and remote sensing pixel size, new methods are required to proportion tree evapotranspiration based on tree fractional canopy area per pixel. We present a novel method to derive tree fractional canopy cover (FTCC) at 20 m resolution in semi-arid and arid floodplain areas. The method employs LiDAR as a canopy area field measurement proxy (10 m resolution). We used Sentinel-1 and Sentinel-2 (radar and multispectral imagery) in a Random Forest analysis, undertaken to develop a predictive FTCC model trained using LiDAR for two regions in the Murray–Darling Basin. A predictor model combining the results of both regions was able to explain between 71%–85% of FTCC variation when compared to LiDAR FTCC when output in 10% increments. Development of this method underpins the advancement of woody vegetation monitoring to inform environmental flow management in the Murray–Darling Basin. The method and fine scale outputs will also be of value to other catchment management concerns such as altered catchment water yields related to bushfires and as such has application to water management worldwide.  相似文献   

European Venus Explorer (EVE): an in-situ mission to Venus   总被引：1，自引：0，他引：1  

E. Chassefière  O. Korablev  T. Imamura  K. H. Baines  C. F. Wilson  D. V. Titov  K. L. Aplin  T. Balint  J. E. Blamont  C. G. Cochrane  Cs. Ferencz  F. Ferri  M. Gerasimov  J. J. Leitner  J. Lopez-Moreno  B. Marty  M. Martynov  S. V. Pogrebenko  A. Rodin  J. A. Whiteway  L. V. Zasova  J. Michaud  R. Bertrand  J.-M. Charbonnier  D. Carbonne  P. Raizonville 《Experimental Astronomy》2009,23(3):741-760

The European Venus Explorer (EVE) mission was proposed to the European Space Agency in 2007, as an M-class mission under the Cosmic Vision Programme. Although it has not been chosen in the 2007 selection round for programmatic reasons, the EVE mission may serve as a useful reference point for future missions, so it is described here. It consists of one balloon platform floating at an altitude of 50–60 km, one descent probe provided by Russia, and an orbiter with a polar orbit which will relay data from the balloon and descent probe, and perform science observations. The balloon type preferred for scientific goals is one which oscillates in altitude through the cloud deck. To achieve this flight profile, the balloon envelope contains a phase change fluid, which results in a flight profile which oscillates in height. The nominal balloon lifetime is 7 days—enough for one full circumnavigation of the planet. The descent probe’s fall through the atmosphere takes 60 min, followed by 30 min of operation on the surface. The key measurement objectives of EVE are: (1) in situ measurement from the balloon of noble gas abundances and stable isotope ratios, to study the record of the evolution of Venus; (2) in situ balloon-borne measurement of cloud particle and gas composition, and their spatial variation, to understand the complex cloud-level chemistry; (3) in situ measurements of environmental parameters and winds (from tracking of the balloon) for one rotation around the planet, to understand atmospheric dynamics and radiative balance in this crucial region. The portfolio of key measurements is complemented by the Russian descent probe, which enables the investigation of the deep atmosphere and surface.  相似文献   

High seas marine protected areas: Benthic environmental conservation priorities from a GIS analysis of global ocean biophysical data     

Peter T. Harris  Tanya Whiteway 《Ocean & Coastal Management》2009,52(1):22-38

Designing a representative network of high seas marine protected areas (MPAs) requires an acceptable scheme to classify the benthic (as well as the pelagic) bioregions of the oceans. Given the lack of sufficient biological information to accomplish this task, we used a multivariate statistical method with 6 biophysical variables (depth, seabed slope, sediment thickness, primary production, bottom water dissolved oxygen and bottom temperature) to objectively classify the ocean floor into 53,713 separate polygons comprising 11 different categories, that we have termed “seascapes”. A cross-check of the seascape classification was carried out by comparing the seascapes with existing maps of seafloor geomorphology and seabed sediment type and by GIS analysis of the number of separate polygons, polygon area and perimeter/area ratio. We conclude that seascapes, derived using a multivariate statistical approach, are biophysically meaningful subdivisions of the ocean floor and can be expected to contain different biological associations, in as much as different geomorphological units do the same. Less than 20% of some seascapes occur in the high seas while other seascapes are largely confined to the high seas, indicating specific types of environment whose protection and conservation will require international cooperation. Our study illustrates how the identification of potential sites for high seas marine protected areas can be accomplished by a simple GIS analysis of seafloor geomorphic and seascape classification maps. Using this approach, maps of seascape and geomorphic heterogeneity were generated in which heterogeneity hotspots identify themselves as MPA candidates. The use of computer-aided mapping tools removes subjectivity in the MPA design process and provides greater confidence to stakeholders that an unbiased result has been achieved.  相似文献   

Evolution of rifted ocean ridges     

Ken C. MacDonald  Tanya M. Atwater 《Earth and Planetary Science Letters》1978,39(3):319-327

A major question in seafloor tectonics has been, how does the 2-km-deep rift valley characteristic of slow-spreading ridges evolve into the relatively horizontal undulating relief of the rift mountains? Deep-tow studies of the Mid-Atlantic Ridge suggest that the primary mechanism for transformation of the rift valley topography is normal faulting along fault planes which dip away from the valley axis. The faulting occurs in a narrow zone just beyond the outer walls of the rift valley. This model allows for a steady-state evolution of the rift valley into the rift mountains in which the state of stress in the oceanic lithosphere continues to be in horizontal deviatoric tension throughout the entire process. Alternate mechanisms involving reverse faulting or regional tilt may be active but are found to be of less importance. Implications for various dynamic models of the rift valley are discussed.  相似文献   

Interarc spreading and Cordilleran tectonics as alternates related to the age of subducted oceanic lithosphere     

Peter Molnar  Tanya Atwater 《Earth and Planetary Science Letters》1978,41(3):330-340

Old, cold oceanic lithosphere is denser and therefore gravitationally more unstable than younger, hotter oceanic lithosphere. Hence, whereas old lithosphere will sink under its own weight, subduction of young lithosphere may require an additional force. Interarc spreading occurs or occurred recently in the western Pacific, in the southern Atlantic, and possibly in the Mediterranean, where the subducted sea floor appears to be more than 50 m.y. old, and in many cases, is more than 100 m.y. old. In most of these regions, the ease with which the old dense lithosphere sinks may have contributed to a seaward migration of the trenches, which led to interarc spreading. Cordilleran tectonics, including high mountains and broad zones of deformation, are present on the margins of the eastern Pacific where the subducted oceanic lithosphere is younger than about 50 m.y. An extra force, which we presume to be necessary to cause subduction of the young lithosphere, may be responsible for the deformation and mountains just as an extra force seems necessary to drive continental collision in Asia. The extensive early Tertiary deformation across a broad zone of western North America may be related to the long-term, continuous subduction of young lithosphere of the Farallon and Kula plates.  相似文献   

The mineralogic transformation of ferrihydrite induced by heterogeneous reaction with bioreduced anthraquinone disulfonate (AQDS) and the role of phosphate     

John M. Zachara  Ravi K. Kukkadapu  Tanya Peretyazhko  Mark Bowden  Chongmin Wang  Dave W. Kennedy  Dean Moore  Bruce Arey 《Geochimica et cosmochimica acta》2011,75(21):6330-6349

Bioreduced anthraquinone-2,6-disulfonate (AH₂DS; dihydro-anthraquinone) was reacted with a 2-line, Si-substituted ferrihydrite under anoxic conditions at neutral pH in PIPES buffer. Phosphate (P) and bicarbonate (C); common adsorptive oxyanions and media/buffer components known to effect ferrihydrite mineralization; and Fe(II)_aq (as a catalytic mineralization agent) were used in comparative experiments. Heterogeneous AH₂DS oxidation coupled with Fe(III) reduction occurred within 0.13-1 day, with mineralogic transformation occurring thereafter. The product suite included lepidocrocite, goethite, and/or magnetite, with proportions varing with reductant:oxidant ratio (r:o) and the presence of P or C. Lepidocrocite was the primary product at low r:o in the absence of P or C, with evidence for multiple formation pathways. Phosphate inhibited reductive recrystallization, while C promoted goethite formation. Stoichiometric magnetite was the sole product at higher r:o in the absence and presence of P. Lepidocrocite was the primary mineralization product in the Fe(II)_aq system, with magnetite observed at near equal amounts when Fe(II) was high [Fe(II)/Fe(III)] = 0.5 and P was absent. P had a greater effect on reductive mineralization in the Fe(II)_aq system, while AQDS was more effective than Fe(II)_aq in promoting magnetite formation. The mineral products of the direct AH₂DS-driven reductive reaction are different from those observed in AH₂DS-ferrihydite systems with metal reducing bacteria, particularly in presence of P.  相似文献   

Source and fractionation controls on subduction-related plutons and dike swarms in southern Patagonia (Torres del Paine area) and the low Nb/Ta of upper crustal igneous rocks     

Othmar?MüntenerEmail authorView author&#;s OrcID profile  Tanya?Ewing  Lukas?P.?Baumgartner  Mélina?Manzini  Thibaud?Roux  Pierre?Pellaud  Luc?Allemann 《Contributions to Mineralogy and Petrology》2018,173(5):38

The subduction system in southern Patagonia provides direct evidence for the variability of the position of an active continental arc with respect to the subducting plate through time, but the consequences on the arc magmatic record are less well studied. Here we present a geochemical and geochronological study on small plutons and dykes from the upper crust of the southern Patagonian Andes at ~?51°S, which formed as a result of the subduction of the Nazca and Antarctic plates beneath the South American continent. In situ U–Pb geochronology on zircons and bulk rock geochemical data of plutonic and dyke rocks are used to constrain the magmatic evolution of the retro-arc over the last 30 Ma. We demonstrate that these combined U–Pb and geochemical data for magmatic rocks track the temporal and spatial migration of the active arc, and associated retro-arc magmatism. Our dataset indicates that the rear-arc area is characterized by small volumes of alkaline basaltic magmas at 29–30 Ma that are characterized by low La/Nb and Th/Nb ratios with negligible arc signatures. Subsequent progressive eastward migration of the active arc culminated with the emplacement of calc-alkaline plutons and dikes?~?17–16 Ma with elevated La/Nb and Th/Nb ratios and typical subduction signatures constraining the easternmost position of the southern Patagonian batholith at that time. Geochemical data on the post-16 Ma igneous rocks including the Torres del Paine laccolith indicate an evolution to transitional K-rich calc-alkaline magmatism at 12.5?±?0.2 Ma. We show that trace element ratios such as Nb/Ta and Dy/Yb systematically decrease with increasing SiO₂, for both the 17–16 Ma calc-alkaline and the 12–13 Ma K-rich transitional magmatism. In contrast, Th/Nb and La/Nb monitor the changes in the source composition of these magmas. We suggest that the transition from the common calc-alkaline to K-rich transitional magmatism involves a change in the source component, while the trace element ratios, such as Nb/Ta and Dy/Yb, of derivative higher silica content liquids are controlled by similar fractionating mineral assemblages. Analysis of a global compilation of Nb/Ta ratios of arc magmatic rocks and simple geochemical models indicate that amphibole and variable amounts of biotite exert a major control on the low Dy/Yb and Nb/Ta of derivative granitic liquids. Lastly, we suggest that the low Nb/Ta ratio of silica-rich magmas is a natural consequence of biotite fractionation and that alternative models such as amphibolite melting in subduction zones and diffusive fractionation are not required to explain the Nb/Ta ratio of the upper continental crust.  相似文献