Bank erosion in an Andean páramo river system: Implications for hydro-development and carbon dynamics in the neotropical Andes     

Derek J.MARTIN  Christopher ELY  Beverley C.WEMPLE 《山地科学学报》2019,(2)

The páramo of the Northern Andes provide critically important ecosystem services to the Northern Andean region in the form of water provisioning and carbon sequestration, both of which are a result of the páramo?s organic-rich soils. Little is known, however, about the hydro-geomorphic characteristics of the rivers that drain these ecosystems. With impending plans for widespread hydro-development and increasing implementation of carbon-sequestering compensation for ecosystem services programs in the region it is imperative that we develop a thorough understanding of the hydrogeomorphic role that rivers play in this unique ecosystem. The objective of this study was to quantify bank erosion along an Amazonian headwater stream draining a small, relatively undisturbed páramo catchment to gain a better understanding of the natural erosion regime and the resulting sediment contributions from this unique ecosystem. This study implemented a combination of field, laboratory, and Geographic Information Systems techniques to quantify bank erosion rates and determine a bank erosion sediment yield from the Ningar River, a small páramo catchment(22.7 km~2) located in the eastern Andean cordillera of Ecuador. Results show that bank erosion rates range from 3.0 to ≥ 390.0 mm/yr, are highly episodic, and yield at least 487 tons of sediment annually to the Ningar River. These results imply that 1) páramo ecosystems substantially contribute to the sediment load of the Amazon River basin; 2) bank erosion is a potentially significant flux component of basin-scale carbon cycles in páramo ecosystems; and 3) hydrologic alteration campaigns(dam building) will likely critically alter these contributions and concomitantly disconnect a critical source of sediment and nutrients to downstream ecosystems.  相似文献   

Holocene deglaciation and recent ice-marginal processes in west Greenland,F. G. M. VAN TATENHOVE,PhD Thesis,Universiteit van Amsterdam 1995; (202 pp) ISBN 90-6787-039-0     

MARTIN KIRKBRIDE 《第四纪科学杂志》1997,12(1):81-82

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AN INTEGRATED APPROACH TO MODELLING HYDROLOGY AND WATER QUALITY IN GLACIERIZED CATCHMENTS     

KEITH RICHARDS  MARTIN SHARP  NEIL ARNOLD  ANGELA GURNELL  MICHAEL CLARK  MARTIN TRANTER  PETER NIENOW  GILES BROWN  IAN WILLIS  WENDY LAWSON 《水文研究》1996,10(4):479-508

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Mountain-wave-induced record low stratospheric temperatures above northern Scandinavia   总被引：1，自引：0，他引：1  

ANDREAS DÖRNBRACK  MARTIN LEUTBECHER  RIGEL KIVI  ESKO. KYRÖ 《地球，A辑:动力气象学与海洋学》1999,51(5):951-963

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A MARITIME RESPONSE TO THE CRISIS IN AREA STUDIES     

MARTIN W. LEWIS  KREN WIGEN 《Geographical review》1999,89(2):161-168

ABSTRACT. The area-studies model of global scholarship, based on dividing the world into a set number of large, quasi-continental regions, is under assault from a variety of intellectual and institutional forces. New, less rigid models of global scholarship are increasingly being called for by both scholars and funding agencies. One useful alternative, currently being explored at Duke University, reframes area studies around ocean and sea basins. Putting maritime interactions at the center of vision brings to light a set of historical regions that have largely remained invisible on the conventional map of the world.  相似文献   

EARLY MODERN EXPANSION AND THE POLITICIZATION OF OCEANIC SPACE*     

ELIZABETH MANCKE 《Geographical review》1999,89(2):225-236

ABSTRACT. The definition of oceans as international politicized space is an integral but little analyzed aspect of early modern European expansion, which took place between about 1450 and 1800. In this essay I explore the implications of thinking about the development of European imperialism and global dominance in oceanic terms. I argue that oceanic, rather than terrestrial, dominance characterized early modern European empires, particularly in relation to Africa and Asia, where indigenous political and economic control prevailed. The long apprenticeship in mastering oceanic space contributed to the ability of Europeans to build land-based empires in Asia and Africa in the nineteenth century. As well, the international relationships worked out by Europeans in the nonstate but militarized arena of the high seas contributed to an emergent global order.  相似文献   

Contrasting P-T Paths in the Eastern Himalaya, Nepal: Inverted Isograds in a Paired Metamorphic Mountain Belt   总被引：1，自引：0，他引：1  

GOSCOMBE  BEN; HAND  MARTIN 《Journal of Petrology》2000,41(12):1673-1719

Petrology and phase equilibria of rocks from two profiles inEastern Nepal from the Lesser Himalayan Sequences, across theMain Central Thrust Zone and into the Greater Himalayan Sequencesreveal a Paired Metamorphic Mountain Belt (PMMB) composed oftwo thrust-bound metamorphic terranes of contrasting metamorphicstyle. At the higher structural level, the Greater HimalayanSequences experienced high-T/moderate-P metamorphism, with ananticlockwise P–T path. Low-P inclusion assemblages ofquartz + hercynitic spinel + sillimanite have been overgrownby peak metamorphic garnet + cordierite + sillimanite assemblagesthat equilibrated at 837 ± 59°C and 6·7 ±1·0 kbar. Matrix minerals are overprinted by numerousmetamorphic reaction textures that document isobaric coolingand re-equilibrated samples preserve evidence of cooling to600 ± 45°C at 5·7 ±1·1 kbar.Below the Main Central Thrust, the Lesser Himalayan Sequencesare a continuous (though inverted) Barrovian sequence of high-P/moderate-Tmetamorphic rocks. Metamorphic zones upwards from the loweststructural levels in the south are: Zone A: albite + chlorite + muscovite ± biotite; Zone B: albite + chlorite + muscovite + biotite + garnet; Zone C: albite + muscovite + biotite + garnet ± chlorite; Zone D: oligoclase + muscovite + biotite + garnet ± kyanite; Zone E: oligoclase + muscovite + biotite + garnet + staurolite+ kyanite; Zone F: bytownite + biotite + garnet + K-feldspar + kyanite± muscovite; Zone G: bytownite + biotite + garnet + K-feldspar + sillimanite+ melt ± kyanite. The Lesser Himalayan Sequences show evidence for a clockwiseP–T path. Peak-P conditions from mineral cores average10·0 ± 1·2 kbar and 557 ± 39°C,and peak-metamorphic conditions from rims average 8·8± 1·1 kbar and 609 ± 42°C in ZonesD–F. Matrix assemblages are overprinted by decompressionreaction textures, and in Zones F and G progress into the sillimanitefield. The two terranes were brought into juxtaposition duringformation of sillimanite–biotite ± gedrite foliationseams (S₃) formed at conditions of 674 ± 33°C and5·7 ± 1·1 kbar. The contrasting averagegeothermal gradients and P–T paths of these two metamorphicterranes suggest they make up a PMMB. The upper-plate positionof the Greater Himalayan Sequences produced an anticlockwiseP–T path, with the high average geothermal gradient beingpossibly due to high radiogenic element content in this terrane.In contrast, the lower-plate Lesser Himalayan Sequences weredeeply buried, metamorphosed in a clockwise P–T path anddisplay inverted isograds as a result of progressive ductileoverthrusting of the hot Greater Himalayan Sequences duringprograde metamorphism. KEY WORDS: thermobarometry; P–T paths; Himalaya; metamorphism; inverted isograds; paired metamorphic belts  相似文献   

Petrogenesis of Archaean Trondhjemites, Tonalites, and Granodiorites from Eastern Finland: Major and Trace Element Geochemistry   总被引：17，自引：4，他引：17  

MARTIN  HERV? 《Journal of Petrology》1987,28(5):921-953

The grey gneisses of eastern Finland form the basement on whichthe Archaean greenstone belts were developed. They are composedof orthogneisses emplaced during two distinct magmatic episodes:2.86 Ga (Kivij?rvi gneisses) and 2.65 (Naavala gneisses). Theirmodal and chemical compositions are those of trondhjemites,tonalites and granodiorites (TTG). Both suites show low-K₂Ocalc-alkaline differentiation trends (trondhjemitic). The aim of this study is to qualify and quantify the successionof different mechanisms by which the TTG series evolved. Theyoungest process was studied first, and the arguments then appliedin order to go back in time to the older ones. For each one,quantification was arrived at with the major elements, and theseresults provided a basis for calculation with the rare earthelements (REE). Finally the whole model was tested with othertrace elements. The petrogenetic model may be summarized as follows: meltingof the upper mantle to form a tholeiitic crust; melting of thesetholeiites transformed into garnet-bearing amphibolites to yieldthe parental magma of the TTG. The residue of the melt consistedof hornblende, plagioclase, clinopyroxene, and garnet with minoramounts of ilmenite and magnetite (10 < F < 30); and fractionalcrystallization of hornblende, plagioclase, and ilmenite withoccasional allanite and/or zircon in small amounts ((1-F) <40). No matter when they were emplaced during the Archaean, all theTTG of this part of the Baltic Shield arose from similar parentalmagmas. The petrogenetic study has shown that garnet and hornblendewere necessarily residual phases during the melting of the Archaeantholeiites. This constraint is very important, as it impliesthat the Archaean geothermal gradients occurring in subduction-zoneswere much higher than in modern times, thus allowing the partialmelting of the subducted oceanic crust.  相似文献   

Bar development in a fluvial sandstone (Westphalian 'A'), Scotland     

MARTIN KIRK 《Sedimentology》1983,30(5):727-742

The fluvial sandstone beneath the Mill Coal in the Westphalian ‘A’ of Scotland erosively overlies a lake mudstone. Slightly erosive surfaces within the sandstone, traceable for over 200 m, are used to divide it into two types of major sedimentary units termed type A and type B. Type A sand units are approximately 200 m wide, up to 7 m thick, convex upward, and lenticular in all directions. The constituent cosets overlap to the ENE and dip mainly at 1–2° downcurrent (NNW), but locally at 10–15°. Where thickest, type A sand units display a vertical facies sequence commencing with trough cross-bedded and massive sandstone, overlain by a thick zone of ripple cross-lamination, a thin zone of trough cross-beds, and a variably eroded silt drape up to 0.4 m thick. Attenuated lateral margins are dominated by flat bedded sandstone with primary current lineation. Type A sand units are interpreted as deposits which were accreted on to a large fluvial bar during successive flood events. The bar is thought to have had a similar topographic significance to sand waves described from the Brahmaputra and slip face bounded bars observed in the South Saskatchewan river. Palaeocurrents measured from trough cross-bed sets 0.3–1.0 m thick within type B sand units indicate flow to the WSW, perpendicular to the palaeoflow direction measured from type A units. In sections perpendicular to the WSW flow direction type B units are lenticular, and in ENE-WSW trending sections they can be traced for over 80 m at a constant thickness. Type B sand units are interpreted as the product of low stage channels which flowed across bar fronts and tops. The sandstone described herein is interpreted as a braided-type river deposit but is atypical, because it is fine grained and has an internal structure dominated by ripple cross-lamination and upper phase plane beds. The palaeoriver is thought to have been of low sinuosity, 7–10 m deep, with a high suspended load and large rapidly fluctuating discharge. At low stage a braided-type flow pattern developed around submerged bars. The regime of the palaeoriver was probably controlled by the fine sediment grain size and humid tropical climate.  相似文献   

Lichenometry in dating recent glacial landforms and deposits, southeast Iceland   总被引：1，自引：0，他引：1  

JOHN E. GORDON  MARTIN SHARP 《Boreas: An International Journal of Quaternary Research》1983,12(3):191-200

Lichenometry curves were derived for the glacier forelands of Breidamerkurjokull and Skalafellsjökull using measurements of the collective species, Rhizocarpon geographicum , from independently dated surfaces deglaciated during the period since the late-19th century ice maximum episode in the area. The form of the curves appears to be linear. Several methods of predicting the ages of undated surfaces were compared for specific test examples, including single lichenometry curves, families of curves and multiple curves based on randomly selected largest lichens. The last method provided a useful means of assessing the reproducibility of predicted ages. Where substrate conditions were highly variable, a lichenometry curve based on single largest lichens provided a preferred result.  相似文献