Holocene pollen assemblages from coastal wetlands: differentiating natural and anthropogenic causes of change in the Thames estuary,UK     

Martyn Waller  Michael J. Grant 《第四纪科学杂志》2012,27(5):461-474

Simultaneous changes in the representation of wetland and dry land taxa are a common feature of mid and late Holocene pollen diagrams from the coastal wetlands of North‐West Europe. Distinguishing both the areas affected and between natural and anthropogenic causes can be problematic. High temporal resolution, improved taxonomic procedures and multivariate statistics have been applied to two Thames estuary sites, along with simulation models, to resolve these issues. Large Poaceae pollen grains appear to be derived from wild grasses rather than cereals, while modelling indicates that even extensive clearance in dry land areas produces relatively minor changes in pollen assemblages where fen carr is the in situ vegetation. It is concluded that rapid/abrupt simultaneous pollen stratigraphic events in coastal wetlands are likely to have been caused by wetland vegetation changes alone. Simultaneous events, dating from c. 2150–1300 cal a BC, can be distinguished at 12 Thames estuary pollen sites. During this interval inter‐tidal environments expanded creating areas attractive to human populations for pasturage. This exploitation is likely to have led to further changes in wetland vegetation and increased clearance activity on adjacent dry land areas. In such circumstances disentangling the processes causing vegetation change is challenging, although considerably aided by the techniques adopted in this paper. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Hydrological footprints of urban developments in the Lake Simcoe watershed,Canada: a combined paired‐catchment and change detection modelling approach          下载免费PDF全文

Stephen K. Oni  Martyn N. Futter  James Buttle  Peter J. Dillon 《水文研究》2015,29(7):1829-1843

Urban sprawl and regional climate variability are major stresses on surface water resources in many places. The Lake Simcoe watershed (LSW) Ontario, Canada, is no exception. The LSW is predominantly agricultural but is experiencing rapid population growth because of its proximity to the Greater Toronto area. This has led to extensive land use changes that have impacted its water resources and altered run‐off patterns in some rivers draining to the lake. Here, we use a paired‐catchment approach, hydrological change detection modelling and remote sensing analysis of satellite images to evaluate the impacts of land use change on the hydrology of the LSW (1994 to 2008). Results show that urbanization increased up to 16% in Lovers Creek, the most urban‐impacted catchment. Annual run‐off from Lovers Creek increased from 239 to 442 mm/year in contrast to the reference catchment (Black River at Washago) where run‐off was relatively stable with an annual mean of 474 mm/year. Increased annual run‐off from Lovers Creek was not accompanied by an increase in annual precipitation. Discriminant function analysis suggests that early (1992–1997; pre‐major development) and late (2004–2009; fully urbanized) periods for Lovers Creek separated mainly based on model parameter sets related to run‐off flashiness and evapotranspiration. As a result, parameterization in either period cannot be used interchangeably to produce credible run‐off simulations in Lovers Creek because of greater scatter between the parameters in canonical space. Separation of early and late‐period parameter sets for the reference catchment was based on climate and snowmelt‐related processes. This suggests that regional climatic variability could be influencing hydrologic change in the reference catchment, whereas urbanization amplified the regional natural hydrologic changes in urbanizing catchments of the LSW. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Vegetation dynamics from a coastal peatland: insights from combined plant macrofossil and pollen data          下载免费PDF全文

Martyn Waller  Richard Early 《第四纪科学杂志》2015,30(8):779-789

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Dynamic cycles,ice streams and their impact on the extent,chronology and deglaciation of the British–Irish ice sheet     

Alun Hubbard  Tom Bradwell  Nicholas Golledge  Adrian Hall  Henry Patton  David Sugden  Rhys Cooper  Martyn Stoker 《Quaternary Science Reviews》2009,28(7-8):758-776

We present results from a suite of forward transient numerical modelling experiments of the British and Irish Ice Sheet (BIIS), consisting of Scottish, Welsh and Irish accumulation centres, spanning the last Glacial period from 38 to 10 ka BP. The 3D thermomechanical model employed uses higher-order physics to solve longitudinal (membrane) stresses and to reproduce grounding-line dynamics. Surface mass balance is derived using a distributed degree-day calculation based on a reference climatology from mean (1961–1990) precipitation and temperature patterns. The model is perturbed from this reference state by a scaled NGRIP oxygen isotope curve and the SPECMAP sea-level reconstruction. Isostatic response to ice loading is computed using an elastic lithosphere/relaxed asthenosphere scheme. A suite of 350 simulations were designed to explore the parameter space of model uncertainties and sensitivities, to yield a subset of experiments that showed close correspondence to offshore and onshore ice-directional indicators, broad BIIS chronology, and the relative sea-level record. Three of these simulations are described in further detail and indicate that the separate ice centres of the modelled BIIS complex are dynamically interdependent during the build up to maximum conditions, but remain largely independent throughout much of the simulation. The modelled BIIS is extremely dynamic, drained mainly by a number of transient but recurrent ice streams which dynamically switch and fluctuate in extent and intensity on a centennial time-scale. A series of binge/purge, advance/retreat, cycles are identified which correspond to alternating periods of relatively cold-based ice, (associated with a high aspect ratio and net growth), and wet-based ice with a lower aspect ratio, characterised by streaming. The timing and dynamics of these events are determined through a combination of basal thermomechanical switching spatially propagated and amplified through longitudinal coupling, but are modulated and phase-lagged to the oscillations within the NGRIP record of climate forcing. Phases of predominant streaming activity coincide with periods of maximum ice extent and are triggered by abrupt transitions from a cold to relatively warm climate, resulting in major iceberg/melt discharge events into the North Sea and Atlantic Ocean. The broad chronology of the modelled BIIS indicates a maximum extent at ～20 ka, with fast-flowing ice across its western and northern sectors that extended to the continental shelf edge. Fast-flowing streams also dominate the Irish Sea and North Sea Basin sectors and impinge onto SW England and East Anglia. From ～19 ka BP deglaciation is achieved in less than 2000 years, discharging the freshwater equivalent of ～2 m global sea-level rise. A much reduced ice sheet centred on Scotland undergoes subsequent retrenchment and a series of advance/retreat cycles into the North Sea Basin from 17 ka onwards, culminating in a sustained Younger Dryas event from 13 to 11.5 ka BP. Modelled ice cover is persistent across the Western and Central Highlands until the last remnant glaciers disappear around 10.5 ka BP.  相似文献   

Hydrological field data from a modeller's perspective: Part 1. Diagnostic tests for model structure     

Hilary K. McMillan  Martyn P. Clark  William B. Bowden  Maurice Duncan  Ross A. Woods 《水文研究》2011,25(4):511-522

Hydrological scientists develop perceptual models of the catchments they study, using field measurements and observations to build an understanding of the dominant processes controlling the hydrological response. However, conceptual and numerical models used to simulate catchment behaviour often fail to take advantage of this knowledge. It is common instead to use a pre‐defined model structure which can only be fitted to the catchment via parameter calibration. In this article, we suggest an alternative approach where different sources of field data are used to build a synthesis of dominant hydrological processes and hence provide recommendations for representing those processes in a time‐stepping simulation model. Using analysis of precipitation, flow and soil moisture data, recommendations are made for a comprehensive set of modelling decisions, including Evapotranspiration (ET) parameterization, vertical drainage threshold and behaviour, depth and water holding capacity of the active soil zone, unsaturated and saturated zone model architecture and deep groundwater flow behaviour. The second article in this two‐part series implements those recommendations and tests the capability of different model sub‐components to represent the observed hydrological processes. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Evolution and palaeosynecology of the Mesozoic earwigs (Insecta: Dermaptera)     

André Nel  Cédric AriaRomain Garrouste  Alain Waller 《Cretaceous Research》2012,33(1):189-195

Sinoprotodiplatys zhangi gen. et sp. nov. is described from the Lower Cretaceous Yixian Formation in Liaoning Province, near Beipiao City, China. It is one of the most recent representatives of the suborder Archidermaptera. The classification and synonymies among the archidermapteran families are reassessed. The palaeosynecological evolution of the Mesozoic earwigs is analysed using the new tool of the ‘Wagner Parsimony using Morphological Characters’ method (‘WAPUM’), suggesting that the evolution of the morphology of these insects was very progressive, perhaps owing to their way of life in the soil.  相似文献   

Geographical variations in the risk of adverse birth outcomes in Spain     

A. Castelló  I. Río  G. López-Abente  P. Fernández-Navarro  J. García-Pérez  L. A. Waller  J. A. Clennon  M. Sandín-Vázquez  F. Bolúmar 《International Journal of Environmental Science and Technology》2014,11(5):1481-1486

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A search for shocked quartz grains in the Allerød‐Younger Dryas boundary layer          下载免费PDF全文

Annelies Van Hoesel  Wim Z. Hoek  Gillian M. Pennock  Knut Kaiser  Oliver Plümper  Michal Jankowski  Maartje F. Hamers  Norbert Schlaak  Mathias Küster  Alexander V. Andronikov  Martyn R. Drury 《Meteoritics & planetary science》2015,50(3):483-498

The Younger Dryas impact hypothesis suggests that multiple airbursts or extraterrestrial impacts occurring at the end of the Allerød interstadial resulted in the Younger Dryas cold period. So far, no reproducible, diagnostic evidence has, however, been reported. Quartz grains containing planar deformation features (known as shocked quartz grains), are considered a reliable indicator for the occurrence of an extraterrestrial impact when found in a geological setting. Although alleged shocked quartz grains have been reported at a possible Allerød‐Younger Dryas boundary layer in Venezuela, the identification of shocked quartz in this layer is ambiguous. To test whether shocked quartz is indeed present in the proposed impact layer, we investigated the quartz fraction of multiple Allerød‐Younger Dryas boundary layers from Europe and North America, where proposed impact markers have been reported. Grains were analyzed using a combination of light and electron microscopy techniques. All samples contained a variable amount of quartz grains with (sub)planar microstructures, often tectonic deformation lamellae. A total of one quartz grain containing planar deformation features was found in our samples. This shocked quartz grain comes from the Usselo palaeosol at Geldrop Aalsterhut, the Netherlands. Scanning electron microscopy cathodoluminescence imaging and transmission electron microscopy imaging, however, show that the planar deformation features in this grain are healed and thus likely to be older than the Allerød‐Younger Dryas boundary. We suggest that this grain was possibly eroded from an older crater or distal ejecta layer and later redeposited in the European sandbelt. The single shocked quartz grain at this moment thus cannot be used to support the Younger Dryas impact hypothesis.  相似文献   

Early extension in the Late Archaean northeastern Eastern Goldfields Province,Yilgarn Craton,Western Australia     

J. R. McIntyre  J. E. Martyn 《Australian Journal of Earth Sciences》2013,60(6):975-992

A series of linked extensional detachments, transfer faults, and sediment- and volcanic-filled half-grabens that pre-date regional folding are described in the Late Archaean Margaret anticline, Eastern Goldfields Province, Yilgarn Craton, Western Australia. Coeval structures and rock units include layer-parallel extensional detachments, transfer faults (high-angle rotational faults rooted in the detachments and linking layer-parallel shear zones with varying amounts of extension); felsic intrusions, either as granitoids emplaced in or below the detachments, or as fine-grained intrusive bodies emplaced above the detachments and controlled by the high-angle faults; and half-grabens controlled by the high-angle faults and filled with clastic sedimentary and volcanic rocks. At least 1500 m of section is excised across the detachments. The detachments and high-angle faults are folded by the east-northeast regional compression that formed the Margaret anticline. Extensional deformation in the Margaret anticline is correlated with the regionally recognised felsic magmatism and associated volcanic and volcaniclastic basin fill dated at approximately 2685–2670 Ma across the Eastern Goldfields Province. This suggests the extensional event was province-wide and post-dated initial greenstone deposition (at around 2705 Ma) but pre-dated regional compressive deformation. We suggest the extension is the result of a thermal anomaly in the crust, generated by the insulating effect of a thick pile (of the order of 10 km or greater) of mafic and ultramafic volcanic rocks on precursor Archaean felsic crust. The thermal anomaly has generated renewed production of felsic and mafic volcanic rocks, coeval with uplift and extension in the upper crust.  相似文献   

Coliform Bacteria in New Jersey Domestic Wells: Influence of Geology,Laboratory, and Method   总被引：1，自引：0，他引：1  

Thomas B. Atherholt  Raymond T. Bousenberry  Gail P. Carter  Leo R. Korn  Judith B. Louis  Michael E. Serfes  Debra A. Waller 《Ground water》2013,51(4):562-574

Following passage of the New Jersey Private Well Testing Act, 50,800 domestic wells were tested between 2002 and 2007 for the presence of total coliform (TC) bacteria. Wells containing TC bacteria were further tested for either fecal coliform or Escherichia coli (FC/E. coli) bacteria. Analysis of the data, generated by 39 laboratories, revealed that the rate of coliform detections in groundwater (GW) was influenced by the laboratory and the method used, and also by geology. Based on one sample per well, TC and FC/E. coli were detected in wells located in bedrock 3 and 3.7 times more frequently, respectively, than in wells located in the unconsolidated strata of the Coastal Plain. In bedrock, detection rates were higher in sedimentary rock than in igneous or metamorphic rock. Ice‐age glaciers also influenced detection rates, most likely by removing material in some areas and depositing thick layers of unconsolidated material in other areas. In bedrock, coliform bacteria were detected more often in wells with a pH of 3 to 6 than in wells with a pH of 7 to 10 whereas the reverse was true in the Coastal Plain. TC and FC/E. coli bacteria were detected in 33 and 9.5%, respectively, of sedimentary rock wells with pH 3 to 6. Conversely, for Coastal Plain wells with pH 3 to 6, detection rates were 4.4% for TC and 0.6% for FC/E. coli.  相似文献