A case study considering the comparability of mass and volumetric suspended sediment data     

Jason A. Hubbart  Elliott Kellner  Graham Freeman 《Environmental Earth Sciences》2014,71(9):4051-4060

Contemporary real-time instruments that advance suspended sediment monitoring capabilities often provide results in units (e.g. volumetric) that are not easily comparable to traditional mass (e.g. gravimetric) methods. A Midwest case study was initiated to assess the accuracy of three methods commonly used to convert volumetric data to mass. Water samples from rural, suburban, and urban stream reaches were analyzed for suspended sediment concentration using laser diffraction and wet sieving methods, resulting in paired volumetric (μl/l) and mass (mg/l) suspended sediment concentrations. Observed volumetric data were converted to mass using an assumed particle density (Pd) of 2.65 g/cm³, a calculated Pd, and linear regression. Using the assumed Pd, estimated mass data differed from observed mass data by as much as 60 %. Dividing mass concentration (mg/l) by the volumetric concentration (μl/l) resulted in site-specific average suspended sediment particle densities ranging from 2.17, 1.99, 1.76 g/cm³ for different land use types. Using a calculated Pd, estimated mass data differed from observed mass data by as much as 45 %. Paired sample t tests showed observed and estimated mass values to be significantly different (p < 0.01). R ² values for regression equations ranged from 0.82 to 0.88. Conversion difficulties likely result from temporal and spatial variations of Pd. The results illustrate the imprecision of conversion methods and highlight possible estimation errors assuming idealized conditions. Continued work is necessary to improve quantitative relationship(s) between mass and volumetric suspended sediment data and the utility of both types of information for science and land management practices.  相似文献   

On Titan’s Xanadu region     

Robert H. Brown  Jason W. Barnes 《Icarus》2011,214(2):556-560

A large, circular marking ∼1800 km across is seen in near-infrared images of Titan. The feature is centered at 10°S, 120°W on Titan, encompasses much of Titan’s western Xanadu region, and has an off-center, quasi-circular, inner margin about 700 km across, with lobate outer margins extending 200-500 km from the inner margin. On the feature’s southern flank is Tui Regio, an area that has very high reflectivity at 5 μm, and is hypothesized to exhibit geologically recent cryovolcanic flows (Barnes, J.W. et al. [2006]. Geophys. Res. Lett. 33), similar to flows seen in Hotei Regio, a cryovolcanic area whose morphology may be controlled by pre-existing, crustal fractures resulting from an ancient impact (Soderblom, L.A. et al. [2009]. Icarus, 204). The spectral reflectivity of the large, circular feature is quite different than that of its surroundings, making it compositionally distinct, and radar measurements of its topography, brightness temperature and volume scattering also suggest that the feature is quite distinct from its surroundings. These and several other lines of evidence, in addition to the feature’s morphology, suggest that it may occupy the site of an ancient impact.  相似文献   

Interannual Variation in Photosynthetically Significant Optical Properties and Water Quality in a Coastal Blackwater River Plume     

Michael J. Durako  Piotr Kowalczuk  Michael A. Mallin  William J. Cooper  Jason J. Souza  David H. Wells 《Estuaries and Coasts》2010,33(6):1430-1441

Surface water optical characteristics, nutrients, and planktonic chlorophyll a concentrations were analyzed in the Cape Fear River (CFR) plume over a 2-year period. CFR discharge during the dry year (109 ± 105 m³s⁻¹) was only 25% of the wet year discharge (429 ± 337 m³s⁻¹). Partitioning the contributions of phytoplankton pigments, non-pigmented particles, and colored dissolved organic matter (CDOM) to the absorption of photosynthetically active radiation (PAR) indicated that CDOM was the dominant contributor to PAR absorption. Particulate absorption was relatively greater during the dry year. Pigment absorption was minor and varied little among stations or between years. Chlorophyll a concentrations were reduced at the most plume-influenced stations during the wet year, despite lower turbidity and higher nitrate concentrations. Ammonium and orthophosphate concentrations were not different between years. CDOM absorption [a _CDOM (412)] ranged from 0.05 to 8.25 m⁻¹ with highest values occurring near the CFR mouth. Our results suggest that for coastal ecosystems with significant blackwater river inputs, CDOM may exert a major limiting influence over near-shore primary production.  相似文献   

Unification Of Non-Dimensional Solutions To Asymptotic Equations For Plumes Of Different Shape     

Peter M. Tate  Jason H. Middleton 《Boundary-Layer Meteorology》2000,94(2):225-251

A model of buoyant fluid rise is developed in aLagrangian framework. Results from the model arevalidated by comparison with laboratory and fieldexperiments. The model is sufficiently general toinclude geometries of any cross-sectional shape. Exact solutions to the asymptotic equations forcontinuous discharges from line and point sources andfor an instantaneous discharge from a point source areconsidered. Prismatic, cylindrical andspherical shapes approximate these three geometries,respectively. Accommodation of these shapes withinthe same general model allows for direct comparison. It is shown that, for discharges into a cross-flowthat may be stratified or unstratified, thenon-dimensional trajectory, thickness and dilution canbe uniquely specified using three parameters. Theseare the non-dimensional size of the source, therelative importance of the initial fluxes of momentumand buoyancy and the number of orthogonal axes throughwhich entrainment can occur. Such non-dimensionalresults are particularly useful for examining thosescenarios for which there are limited experimentaldata.  相似文献   

The Glaciolacustrine Landform–Sediment Assemblage at Heinabergsjökull, Iceland     

Matthew R. Bennett  David Huddart  & Tom McCormick 《Geografiska Annaler: Series A, Physical Geography》2000,82(1):1-16

Landform–sediment assemblages associated with two ice-dammed lakes, one active and one fossil, at Heinabergsjökull in southeast Iceland are described. The current ice-dammed lake (Vatnsdalur) is dominated by a large aggradational terrace, as well as an excellent suite of shorelines. The second fossil ice-dammed lake dates from the Neoglacial maximum of Heinabergsjökull ( c . 1887) and drained during the late 1920s. This lake is associated with a suite of shorelines and ice-marginal glaciolacustrine fans. The sedimentology of one of these fans is described. Between 50 and 70% of the sediment succession is dominated by ice-rafted sediment, although rhythmites, matrix-rich gravels, sands and graded sand–silt couplets are also present. A range of intra-formational, soft-sediment deformation structures are present, consistent with liquefaction and deformation associated with loading, current shear, and iceberg calving. The landform–sediment assemblages described from Heinabergsjökull provide important data for the interpretation of Pleistocene ice-dammed lakes.  相似文献   

Thermal detection of discrete riparian inflow points (DRIPs) during contrasting hydrological events          下载免费PDF全文

Stefan W. Ploum  Jason A. Leach  Lenka Kuglerová  Hjalmar Laudon 《水文研究》2018,32(19):3049-3050

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A conceptual model of supra‐glacial lake formation on debris‐covered glaciers based on GPR facies analysis          下载免费PDF全文

Jordan R. Mertes  Sarah S. Thompson  Adam D. Booth  Jason D. Gulley  Douglas I. Benn 《地球表面变化过程与地形》2017,42(6):903-914

Supra‐glacial lakes and ponds can create hotspots of mass loss on debris‐covered glaciers. While much research has been directed at understanding lateral lake expansion, little is known about the rates or processes governing lake deepening. To a large degree, this knowledge gap persists due to sparse observations of lake beds. Here we report on the novel use of ground penetrating radar (GPR) surveys to simultaneously collect supra‐glacial lake bathymetry and bottom composition data from Spillway Lake (surface area of 2.4 × 10⁵ m²; volume of 9.5 × 10⁴ m³), which is located in the terminus region of the Ngozumpa Glacier in the Khumbu region of the Nepal Himalaya. We identified two GPR bottom signals corresponding to two sedimentary facies of (1) sub‐horizontal layered fine sediment drape and (2) coarse blocky diamict. We provide an understanding of the changes in subaqueous debris distribution that occur through stages of lake expansion by combining the GPR results with in situ observations of shoreline deposits matching the interpreted facies. From this, we present an updated conceptual model of supra‐glacial lake evolution, with the addition of data on the evolving debris environment, showing how dominant depositional processes can change as lakes evolve from perched lakes to multi‐basin base‐level lakes and finally onto large moraine‐dammed lakes. Throughout lake evolution, processes such as shoreline steepening, lakebed collapse into voids and conduit interception, subaerial and subaqueous calving and rapid areal expansion alter the spatial distribution and makeup of lakebed debris and sediments forcing a number of positive and negative feedbacks on lake expansion. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Bison hunting at Cooper Site: Where lightning bolts drew thundering herds     

Jason Labelle 《Geoarchaeology》2000,15(4):375-377

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Architecture of a distal pre-vegetation braidplain: Cambrian middle member of the Wood Canyon Formation,southern Marble Mountains,California, USA     

Jason G. Muhlbauer  Christopher M. Fedo  Jeffrey E. Moersch 《Sedimentology》2020,67(2):1084-1113

Architectural element analysis and detailed mapping of a 300 m along-strike exposure of the middle member Wood Canyon Formation, southern Marble Mountains, California, USA, provides new evidence for extensive braided–fluvial channel-belt deposits with adjacent overbank environments. Three-dimensional models constructed using ‘Structure from Motion’ techniques, combined with field-based observations, allowed interpretation of outcrop-scale trends, barforms, channel fills and fine-scale features. The ca 80 m thick member is divisible into five distinct units, including units M1 to M3 that form the bulk of the stratigraphy. Units are defined by stacking patterns of three facies associations (Facies Association 1 to Facies Association 3), each representing the product of a subenvironment within the fluvial system. In Facies Association 1, stacked cosets, interpreted as low-relief fluvial bars and channel fills, preserve vertical-accretion and downstream-accretion elements under unimodal north-north-west palaeoflow, with minor lateral accretion near bar edges. Deposits of Facies Association 2 to Facies Association 3, linked to overbank environments, are found only in unit M2, in the middle 27 m of the middle member. Floodplains, represented by Facies Association 2, include crumbly red-orange intervals of fine to medium-grained sandstone and thinner sets of cross-bedding than Facies Association 1, interbedded with thicker cross-stratification indicative of overbank splay or overland flow aggradation from adjacent channel belts during flood stage. Possible aeolian beds of Facies Association 3 preserve broad festooned trough cross-strata that average 23 cm in thickness; their small size, medium-grained sandstone and iron oxide cement suggest a high water table. The diverse assemblage of interpreted subenvironments, paired with bedform and facies patterns, implies a perennial fluvial system that gradually built large sand bars as the channel belt migrated and avulsed across an unconfined braided–fluvial reach, leaving the overbank area on its flanks subject to weathering and aeolian transport. Despite the occurrence of strata deposited in low-energy and ponded settings, and a marine influence proposed for nearby sections of middle member, no ichnofossils were encountered.  相似文献