Decadal changes in distribution and frequency of wood in a free meandering river,the Ain River,France     

Neil S. Lassettre  Herv Pigay  Simon Dufour  Anne‐Julia Rollet 《地球表面变化过程与地形》2008,33(7):1098-1112

This study examined the temporal dynamics and longitudinal distribution of wood over a multi‐decadal timescale at the river reach scale (36 km) and a meander bend scale (300–600 m) in the Ain River, a large gravel‐bed river flowing through a forested corridor, and adjusting to regulation and floodplain land‐use change. At the 36 km scale, more wood was recruited by bank erosion in 1991–2000 than since the 1950s. The longitudinal distribution of accumulations was similar between 1989 and 1999, but in both years individual pieces occurred homogeneously throughout the reach, while jam distribution was localized, associated with large concave banks. A relationship between the mean number of pieces and the volume recruited by bank erosion (r² = 0·97) indicated a spatial relationship between areas of wood production and storage. Wood mass stored and produced and channel sinuosity increased from 1993 to 2004 at three meander bends. Sinuosity was related to wood mass recruited by bank erosion during the previous decade (r² = 0·73) and both of these parameters were correlated to the mean mass of wood/plot (r² = 0·98 and 0·69 respectively), appearing to control wood storage and delivery at the bend scale. This suggests a local origin of wood stored in channel, not input from upstream trapped by preferential sites. The increase in wood since 1950 is a response to floodplain afforestation, to a change from braided to meandering channel pattern in response to regulation, and to recent large floods. We observed temporal stability of supply and depositional sectors over a decade (on a reach scale). Meander bends were major storage sites, trapping wood with concave banks, also delivering wood. These results, and the link between sinuosity and wood frequency, establish geomorphology as a dominant wood storage and recruitment control in large gravel‐bed rivers. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Reply to Comment on: Coarse clast ridge sequences as suitable archives for past storm events? Case study on the Houtman Abrolhos,Western Australia     

Anja M. Scheffers  Sander R. Scheffers  Dieter H. Kelletat  Peter Squire  Lindsay Collins  Yuexing Feng  Jian‐Xin Zhao  Renaud Joannes‐Boyau  Simon Matthias May  Gerhard Schellmann  Heather Freeman 《第四纪科学杂志》2013,28(2):213-215

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High‐frequency precipitation and stream water quality time series from Plynlimon,Wales: an openly accessible data resource spanning the periodic table     

Colin Neal  Brian Reynolds  James W. Kirchner  Phil Rowland  Dave Norris  Darren Sleep  Alan Lawlor  Clive Woods  Sarah Thacker  Hayley Guyatt  Colin Vincent  Kathryn Lehto  Simon Grant  Jeremy Williams  Margaret Neal  Heather Wickham  Sarah Harman  Linda Armstrong 《水文研究》2013,27(17):2531-2539

This scientific briefing announces the availability of a new multi‐element high‐frequency water quality data set that is openly accessible to the research community. The data set comprises up to 2 years of 7‐hourly water quality data for two streams and one rainfall site in the Upper Severn catchment at Plynlimon in Mid‐Wales. The measurements cover 50 analytes ranging from H⁺ to U and spanning six orders of magnitude in concentration, including major, minor and trace elements as well as nutrients, and they complement decades of weekly measurements of the same analytes at the Upper Severn. Together, the weekly and 7‐hourly time series provide a unique data set for studying both long‐term trends and short‐term dynamics. The data show complex behaviour over a wide range of timescales, challenging our understanding of catchment processes and informing future modelling efforts. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Pore system characterisation in heterogeneous carbonates: An alternative approach to widely-used rock-typing methodologies     

Cathy Hollis  Volker Vahrenkamp  Simon Tull  Abhijit Mookerjee  Conxita Taberner  Yaduo Huang 《Marine and Petroleum Geology》2010,27(4):772-793

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Holocene palaeoceanographic changes in Barrow Strait,Canadian Arctic: foraminiferal evidence     

Thomas R. Gregory  Christopher W. Smart  Malcolm B. Hart  Guillaume Massé  Lindsay L. Vare  Simon T. Belt 《第四纪科学杂志》2010,25(6):903-910

Holocene changes in the benthic and planktic foraminiferal fauna (>63 µm) from a marine sediment core (ARC‐3 Canadian Arctic Archipelago, 74° 16.050′ N, 91° 06.380′ W, water depth 347 m) show that significant environmental and palaeoceanographic variations occurred during the last 10 ka. Foraminiferal assemblages are restricted to the ca. 4.5–10 ka interval as younger samples are mostly barren of foraminifera due to intense carbonate dissolution after ca. 4.5 ka. Foraminiferal assemblages in the ca. 4.5–10 ka interval are dominated by the benthic species Islandiella helenae and Cassidulina reniforme (57% of total), with Elphidium clavatum, Cibicides lobatulus and Buccella frigida also being common in this interval. The dominance of these species indicates a seasonal sea ice regime which is consistent with the occurrence of the sea ice diatom‐derived organic geochemical biomarker IP₂₅ throughout the core. The abundances of C. reniforme and E. clavatum decline upcore; consistent with more frequent mixing of the Barrow Strait water column during the early Holocene. It is likely that the influence of CO₂‐rich Arctic surface water masses have caused an increase in bottom water corrosivity after ca. 8.5 ka, and dissolution has been further enhanced by sea ice‐related processes after ca. 6 ka, concomitant with increased IP₂₅ fluxes. Dissolution is strongest when IP₂₅ fluxes are highest, suggesting a link between the sea ice and benthic systems. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

A new strategy for analyzing the chronometry of constructed rock features in deserts     

Niccole Villa Cerveny  Russell Kaldenberg  Judyth Reed  David S. Whitley  Joseph Simon  Ronald I. Dorn 《Geoarchaeology》2006,21(3):281-303

The western Great Basin contains thousands of constructed rock features, including rock rings, cairns, and alignments. Unlike subtractive geoglyphs, such as the Nasca Lines of Peru, that remove desert pavement, these surface features alter the location and positioning of cobble‐ to bouldersized rocks. The chronology of surface rock features has remained unconstrained by numerical ages because no prior chronometric approach has been able to yield age control. We propose a new strategy for studying these features by analyzing anthropogenic modifications to rock coatings, an approach that permits the use of several dating methods, two of which are assessed here: radiocarbon dating of pedogenic carbonate and rock‐varnish microlaminations. Initial results from Searles Valley, eastern California, suggest that constructed rock features may be as old as early Holocene and terminal Pleistocene. Archaeological surveys of desert areas would be greatly enhanced if they noted altered positions of rock coatings. © 2006 Wiley Periodicals, Inc.  相似文献   

An innovative application of the Kinect in Earth sciences: quantifying deformation in analogue modelling of volcanoes     

Riccardo Tortini  Fabio L. Bonali  Claudia Corazzato  Simon A. Carn  Alessandro Tibaldi 《地学学报》2014,26(4):273-281

Measuring surface deformation is critical in analogue modelling of Earth science phenomena. Here, we present a novel application of the Microsoft Kinect sensor to measure vertical deformation in a scaled analogue model of Nisyros volcano (Greece), simulating two magmatic sources and related surface deformation. The Kinect permits capture of real time, 640 × 480 pixel, true‐colour images (RGB) and a grid of distances to the modelled surface with a horizontal and vertical resolution of ±1 mm. Using recorded distances permits quantification of vertical deformation in terms of maximum and average down‐ and uplift during deflation and inflation phases respectively, which is of crucial importance for defining the kinematics of faults formed during the modelling, determined from interpretation of the RGB images. Although other techniques have demonstrated similar or higher accuracy, our study demonstrates the cost‐effectiveness of the Kinect in analogue modelling of volcanoes.  相似文献   

Storm event sediment fingerprinting for temporal and spatial sediment source tracing     

Simon S. Vale  Ian C. Fuller  Jonathan N. Procter  Les R. Basher  John R. Dymond 《水文研究》2020,34(15):3370-3386

Sediment fingerprinting has been widely used to distinguish discrete sediment sources; however, application to intra-storm sediment source variability has received relatively little focus despite the benefit being long recognized. In this investigation, sediment fingerprinting was applied to a 53-hr storm event sampled hourly to determine sediment source dynamics throughout the event. Sediment sources were differentiated using 16 variables, and source contribution determined using Bayesian and Frequentist mixing models for comparison. Both models provided comparable source predictions for the dominant source estimates and the general temporal pattern. The Frequentist model appeared to exhibit some unreliable values coinciding with low GOF and attributed to inherent model structure. The Bayesian model showed higher uncertainty, likely due to the “process error” utilized associated with single sample mixtures. High variability in sediment source contribution was observed between hourly time steps; however, local smoothing reveals temporal trends during the event. A higher average proportion of mudstone is found in the falling limb (0.544) compared with the rising limb (0.464), and the reverse is observed for mountain range (0.218 vs. 0.283) and unconsolidated (0.073 vs. 0.055). In the initial hours of the storm, mudstone source contribution significantly drops, whereas mountain range and unconsolidated contributions peak. The SSC-Q clockwise hysteresis indicates proximal sediment sources, suggesting the mudstone sediment is stored channel sediment and easily entrained. This sediment flushes through, coinciding with a drop as the distal mountain range and unconsolidated sources arrive to peak contribution. The wider Manawatū discharge and sediment load then arrive, delivering increasing levels of mudstone throughout the remainder of the event while mountain range sediment diminishes. Spatial representation of the sediment source contribution was derived from distributing sediment source loads to the spatial extent of the source material according to sub-catchment sediment loads and was weighted according to slope. This provided an effective means to visualize the origin of the sediment and a better spatial interpretation of sediment fingerprinting results, which is typically limited by poor spatial resolution.  相似文献   

Discussion about the validity of sharp‐interface models to deal with seawater intrusion in coastal aquifers          下载免费PDF全文

Carlos Llopis‐Albert  David Pulido‐Velazquez 《水文研究》2014,28(10):3642-3654

Analytical models have been exhaustively used to study simple seawater intrusion problems and the sustainable management of groundwater resources in coastal aquifers because of its simplicity, easy implementation, and low computational cost. Most of these models are based on the sharp‐interface approximation and the Ghyben–Herzberg relation, and their governing equations are expressed in terms of a single potential theory to calculate critical pumping rates in a coastal pumping scenario. The Ghyben–Herzberg approach neglects mixing of fresh water and seawater and implicitly assumes that salt water remains static. Therefore, the results of the analytical solutions may be inaccurate and unacceptable for some real‐complex case studies. This paper provides insight into the validity of sharp‐interface models to deal with seawater intrusion in coastal aquifers, i.e. when they can be applied to obtain accurate enough results. For that purpose, this work compares sharp‐interface solutions, based on the Ghyben–Herzberg approach, with numerical three‐dimensional variable‐density flow simulations for a set of heterogeneous groundwater flow and mass transport parameters, and different scenarios of spatially distributed recharge values and spatial wells placement. The numerical experiment has been carried out in a 3D unconfined synthetic aquifer using the finite difference numerical code SEAWAT for solving the coupled partial differential equations of flow and density‐dependent transport. This paper finds under which situations the sharp‐interface solution gives good predictions in terms of seawater penetration, transition zone width and critical pumping rates. Additionally, the simulation runs indicate to which parameters and scenarios the results are more sensitive. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Late Pleistocene palaeolake in the interior of Oman: a potential key area for the dispersal of anatomically modern humans out‐of‐Africa?     

Thomas M. Rosenberg  Frank Preusser  Ingo Blechschmidt  Dominik Fleitmann  Reto Jagher  Albert Matter 《第四纪科学杂志》2012,27(1):13-16

Relict fluvial and lacustrine deposits in the interior of Oman near Saiwan consist of waterlain breccias with pebble imbrications and current ripples, covered by algal laminites containing calcified reeds and charcoal pieces. Geomorphological evidence suggests that the palaeolake covered a maximum surface of 1400 km² and had a maximum depth of about 25 m. Optically stimulated luminescence (OSL) and thermally transferred OSL dating indicate that this palaeolake existed sometime between 132 and 104 ka. The rich archaeological evidence in the area suggests substantial human occupation, possibly at the time when Palaeolake Saiwan existed. Interestingly, the lithic traditions of the archaeological material show no clear relation to coeval findings from neighbouring areas, putting a question mark on the origin of the culture found at Saiwan. This finding raises questions concerning the origin of the population inhabiting Saiwan, as the site lies along one possible route for the dispersal of anatomically modern humans out‐of‐Africa. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献