Net aboveground primary production and soil properties of floating and attached freshwater tidal marshes in the Río de la Plata estuary,Argentina     

Paula Pratolongo  Patricia Kandus  Mark M. Brinson 《Estuaries and Coasts》2007,30(4):618-626

In the lower delta of the Paraná River, at the head of the Río de la Plata estuary (Argentina), we compared net aboveground primary production (NAPP) and soil properties of the dominant macrophyteScirpus giganteus (Kunth) in a floating and an attached marsh community. Both marshes are tidally influenced but in different ways. The floating marsh site is relatively isolated from tidal influences because its ability to float makes it resistant to overland flow and to sediment inputs from the estuary. The attached marsh lacks the capacity to float and receives sediment supplies from the estuary through overland flow. These hydrologic differences are reflected in lower mineral content in sediments of the floating marsh. Using a leaf tagging technique, estimated NAPP was 1,109 ± 206 g m⁻² yr⁻¹ for the floating marsh and 1,866 ±258 g m⁻² yr⁻¹ for the attached marsh. We attribute the lower NAPP of the floating marsh to isolation from sediment input from overland flow.  相似文献   

河西走廊早新生代红层次生剩磁及其对原生剩磁影响评价          下载免费PDF全文

戴霜  方小敏  Mark Dekkers  程彧  唐玉虎  朱强 《地球物理学进展》2007,22(6):1760-1766

系统研究了河西走廊火烧沟组陆相红层200个采点岩石的热退磁行为和17个代表性样品的岩石磁学特征,结果表明有102个采点可以分离出A、B、C三个剩磁分量,有82个采点只有一个分量(C分量),16个采点只能分离出A、B分量.A、B分量分别由针铁矿和磁赤铁矿携带,C分量在砂岩中由磁铁矿携带,在泥质砂岩和泥岩中由磁铁矿和赤铁矿共同携带.A、B分量剩磁方向随机分布,不能获得置信水平的古地磁平均方向,为次生剩磁.它们的存在并不影响岩石原生剩磁的分离,也不影响原生剩磁信号的稳定性和获得的古地磁数据的可靠性.16个砂岩采点中不能分离出C分量,是由于后生的赤铁矿彻底改变了由磁铁矿携带的原生剩磁组分,在高密度采样的情况下剔除这些采点并不影响古地磁极性柱的构建和解释.  相似文献   

High‐resolution interpretative geomorphological mapping of river valley environments using airborne LiDAR data     

Anna F. Jones  Paul A. Brewer  Eric Johnstone  Mark G. Macklin 《地球表面变化过程与地形》2007,32(10):1574-1592

The availability of airborne LiDAR data provides a new opportunity to overcome some of the problems associated with traditional, field‐based, geomorphological mapping such as restrictions on access and constraints of time or cost. The combination of airborne LiDAR data and GIS technology facilitates the rapid production of geomorphological maps of floodplain environments; however, unfiltered LiDAR data, which include vegetation and buildings, are currently more suitable for geomorphological mapping than data that have been filtered to remove these features. Classification of LiDAR data according to elevation in a GIS enables the user to identify and delineate geomorphological features in a manner similar to field mapping, but it is necessary to use a range of classification intervals in order to map the various types of feature that occur within a single reach. Comparison of a LiDAR‐derived geomorphological map with an independently produced field geomorphological map showed a high degree of similarity between the results of the two methods, although ground‐truthing is essential in cases where a high degree of accuracy is required. Ground‐truthing of a LiDAR‐derived geomorphological map showed that around 80% of features mapped using both methods were identified from the LiDAR data, suggesting that the method is suitable for applications such as production of base maps for use in field mapping and selection of sites for detailed investigation. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Characteristics of deep groundwater flow in a basin marginal setting at Sellafield,Northwest England: Cl and halide evidence     

Richard Metcalfe  Mark B. Crawford  Adrian H. Bath  Anna K. Littleboy  Paul J. Degnan  Hugh G. Richards 《Applied Geochemistry》2007

A number of chemical and physical processes inside and outside a sedimentary basin (e.g. evaporite dissolution and topographic drive, respectively) affect groundwater flow near the basin’s margin. Contrasting formations at the margin, typically basinal sedimentary rocks and basement, are host to the interplay between these processes so that groundwater flows and compositions change within a relatively small volume. To interpret how groundwater flow and geochemistry have evolved, interactions between these processes must be understood. Such interactions were investigated near the margin of the East Irish Sea Basin in NW England, by sampling deep groundwaters (to 1500 m below sea level) from Ordovician volcanic basement rocks and Carboniferous to Triassic sedimentary cover rocks. Variable Br/Cl ratios and Cl concentrations in deep saline waters and brines indicate mixing patterns. Variations in ³⁶Cl/Cl constrain the timing of mixing. Relatively low Br/Cl ratios (ca. 1 × 10⁻³ by mass) characterise brine from the western sedimentary cover and reflect halite dissolution further west. Saline water with relatively high Br/Cl ratios (ca. 2 × 10⁻³ by mass) of uncertain origin occupies the eastern basement. These two waters mix across the area. However, mixing alone cannot explain variable ³⁶Cl/Cl ratios, which partly reflect differing in situ³⁶Cl production rates in different rock formations. Most ³⁶Cl/Cl ratios in groundwater sampled from the eastern metavolcanic basement (mean = 25 × 10⁻¹⁵) and western sedimentary cover (mean = 10 × 10⁻¹⁵) are at or close to equilibrium with in situ³⁶Cl production. These variations in ³⁶Cl/Cl across the site possibly took >1.5 Ma to be attained, implying that deep groundwater flow responded only slowly to the Quaternary glaciation of the site. Interplay between varied processes in basin marginal settings does not necessarily imply flow instability.  相似文献   

Predicting the future carbon budget of an upland peat catchment     

Fred Worrall  Tim Burt  John Adamson  Mark Reed  Jeff Warburton  Alona Armstrong  Martin Evans 《Climatic change》2007,85(1-2):139-158

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The potential role of wound-activated volatile release in the chemical defence of the brown alga <Emphasis Type="Italic">Dictyota dichotoma</Emphasis>: Blend recognition by marine herbivores     

Theresa Wiesemeier  Mark Hay  Georg Pohnert 《Aquatic Sciences - Research Across Boundaries》2007,69(3):403-412

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Editorial: Special Issue on Tropical Cyclones     

Lance M. Leslie  David J. Karoly  Mark Leplastrier  Lixin Qi 《Meteorology and Atmospheric Physics》2007,97(1-4):1-1

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Clay mineral‐organic matter relationships in the early solar system     

Victoria K. Pearson  Mark A. Sephton  Anton T. Kearsley  Philip A. Bland  Ian A. Franchi  Iain Gilmour 《Meteoritics & planetary science》2002,37(12):1829-1833

Abstract— As the solar system formed, it inherited and perpetuated a rich organic chemistry, the molecular products of which are preserved in ancient extraterrestrial objects such as carbonaceous chondrites. These organic‐rich meteorites provide a valuable and tangible record of the chemical steps taken towards the origin of life in the early solar system. Chondritic organic matter is present in the inorganic meteorite matrix which, in the CM and CI chondrites, contains evidence of alteration by liquid water on the parent asteroid. An unanswered and fundamental question is to what extent did the organic matter and inorganic products of aqueous alteration interact or display interdependence? We have used an organic labelling technique to reveal that the meteoritic organic matter is strongly associated with clay minerals. This association suggests that clay minerals may have had an important trapping and possibly catalytic role in chemical evolution in the early solar system prior to the origin of life on the early Earth.  相似文献   

Model intercomparison study to investigate a dense contaminant plume in a complex hydrogeologic system     

Mark D. Williams  Charles R. Cole  Michael G. Foley  Galina A. Zinina  Alexander I. Zinin  Nelly A. Vasil'kova  Lilia M. Samsonova 《Environmental Geology》2002,42(2-3):199-213

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STJ observations of the eclipsing polar HU Aqr     

C. M. Bridge  Mark Cropper  Gavin Ramsay  M. A. C. Perryman  J. H. J. de Bruijne  F. Favata  A. Peacock  N. Rando  A. P. Reynolds 《Monthly notices of the Royal Astronomical Society》2002,336(4):1129-1138

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