Elm bark beetle in Holocene peat deposits and the northwest European elm decline     

Sarah H. E. Clark  Kevin J. Edwards 《第四纪科学杂志》2004,19(6):525-528

The elm decline of 5000 ¹⁴C yr ago has been the most widely discussed phenomenon in post‐glacial vegetation history. This pan‐European reduction of elm populations, echoed in the decimation of elmwoods in Europe during the twentieth century, has attracted a series of interrelated hypotheses involving climate change, human activity, disease and soil deterioration. The elm bark beetle (Scolytus scolytus L.) is an essential component of disease explanations. We present evidence for the presence of the beetle over a prolonged period (ca. 7950–4910 yr BP [8800–5660 cal. yr BP]) from a lowland raised mire deposit in northeast Scotland, with its final appearance at this site, and the first and only appearance in another mire of a single scolytid find, around the time of the elm decline. The subfossil S. scolytus finds are not only the first from Scotland, but they also represent the most comprehensive sequence of finds anywhere. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Nutrient transports in a Swedish estuary     

Wayne Wilmot  Peter Toll  Björn Kjerfve 《Estuarine, Coastal and Shelf Science》1985,21(2):161-184

Himmerfjärd is a Swedish estuary bordering on the Baltic. The estuary lacks astronomical tides and its circulation is driven by winds and freshwater runoff. Because of a tertiary sewage treatment plant located at its inner end, the estuary is becoming increasingly eutrophic. A field study was carried out for a 78-day period in late summer and early fall of 1977 to determine rates of nutrient transport and to construct nutrient budgets. Since physical parameters (current velocity, temperature, salinity, winds and water level changes) were measured more frequently than nutrients (phosphate, nitrate, nitrite and ammonium) it was necessary to develop a suitable method to calculate nutrient flux time series and net nutrient fluxes. Over the study period, Himmerfjärd imported phosphorus and exported nitrogen. Direction of nutrient fluxes and changes in flux direction were consistent with the structure of the baroclinic currents.  相似文献   

QUEST on DASI: a South Pole CMB polarization experiment     

Sarah Church  Peter Ade  James Bock  Melanie Bowden  John Carlstrom  Ken Ganga  Walter Gear  James Hinderks  Wayne Hu  Brian Keating  John Kovac  Andrew Lange  Eric Leitch  Olivier Mallie  Simon Melhuish  Anthony Murphy  Ben Rusholme  Creidhe O&#x;Sullivan  Lucio Piccirillo  Clem Pryke  Andy Taylor  Keith Thompson 《New Astronomy Reviews》2003,47(11-12):1083

QUEST on DASI is a ground-based, high-sensitivity, high-resolution (ℓ_max2500) experiment designed to map CMB polarization at 100 and 150 GHz and to measure the power spectra from E-modes, B-modes from lensing of the CMB, and B-modes from primordial gravitational waves. The experiment comprises a 2.6 m Cassegrain optical system, equipped with an array of 62 polarization-sensitive bolometers (PSBs), located at the South Pole. The instrument is designed to minimize systematic effects; features include differencing of pairs of orthogonal PSBs within a single feed, a rotatable achromatic waveplate, and axisymmetric rotatable optics. In addition the South Pole location allows both repeatable and highly controlled observations. QUEST on DASI will commence operation in early 2005.  相似文献   

Downstream geomorphic impacts of large dams: the case of Glenbawn Dam,NSW     

Wayne D. Erskine 《Applied geography (Sevenoaks, England)》1985,5(3):195-210

Downstream hydrologic effects since the closure of Glenbawn Dam, a large dual-purpose storage for water conservation and flood mitigation, include: (i) a reduction in mean annual runoff of about 21 × 10⁶ m³; (ii) a change in the probability distribution of mean daily flows involving a truncation of flows >;8 × 10⁶ m³ d^?1, a much reduced frequency of flows >7 × 10⁵ m³ d^?1 and an increased frequency of flows <7 × 10⁵ m³ d^?1; and (iii) a reduction in flood magnitude of at least 80 per cent for all probabilities of exceedance. From suspended sediment samples collected before and after dam closure, sediment trap efficiency has been estimated at 99 per cent.An accommodation adjustment of the channel has occurred upstream of the first unregulated tributary because the bed is armoured, the banks are well vegetated, some bedrock and concrete controls are present and all regulated releases are incompetent to transport the bed material. Immediately downstream of the first unregulated tributary, the channel has contracted by up to 45 per cent and degraded by up to 69 per cent during lateral migration. Further downstream no channel changes were recorded although the bed material has progressively coarsened over time.  相似文献   

Ice‐cover variability on shallow lakes at high latitudes: model simulations and observations     

Claude R. Duguay  Greg M. Flato  Martin O. Jeffries  Patrick Mnard  Kim Morris  Wayne R. Rouse 《水文研究》2003,17(17):3465-3483

A one‐dimensional thermodynamic model for simulating lake‐ice phenology is presented and evaluated. The model can be driven with observed daily or hourly atmospheric forcing of air temperature, relative humidity, wind speed, cloud amount and snowfall. In addition to computing the energy balance components, key model output includes the temperature profile at an arbitrary number of levels within the ice/snow (or the water temperature if there is no ice) and ice thickness (clear ice and snow‐ice) on a daily basis, as well as freeze‐up and break‐up dates. The lake‐ice model is used to simulate ice‐growth processes on shallow lakes in arctic, sub‐arctic, and high‐boreal forest environments. Model output is compared with field and remote sensing observations gathered over several ice seasons. Simulated ice thickness, including snow‐ice formation, compares favourably with field measurements. Ice‐on and ice‐off dates are also well simulated when compared with field and satellite observations, with a mean absolute difference of 2 days. Model simulations and observations illustrate the key role that snow cover plays on the seasonal evolution of ice thickness and the timing of spring break‐up. It is also shown that lake morphometry, depth in particular, is a determinant of ice‐off dates for shallow lakes at high latitudes. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

High resolution paleoenvironmental and chronological investigations of Norse landnám at Tasiusaq, Eastern Settlement, Greenland     

Kevin J. Edwards  J. Edward Schofield 《Quaternary Research》2008,69(1):1-15

High-resolution paleoenvironmental data from a peat profile with a small pollen source area are used to reconstruct the impacts of landnám on vegetation and soils at a Norse farm complex (∅2 at Tasiusaq) comprising two farms in the Eastern Settlement of Greenland. Analyses include the AMS ¹⁴C dating of plant macrofossil samples and the use of Bayesian radiocarbon calibration to construct improved age-depth models for Norse cultural horizons. The onset of a regional landnám may be indicated by the clearance of Betula pubescens woodland immediately prior to local settlement. The latter is dated to AD 950-1020 (2σ) and is characterised by possible burning of Betula glandulosa scrub to provide grassland pasture for domestic stock. Clearance and grazing resulted in accelerated levels of soil erosion at a westerly farm. This was followed by an easterly migration of settlement and agriculture. Site constraints prevent an assessment of the demise of the easterly farm, but pressures of overgrazing and land degradation may have been the major factors responsible for the abandonment of the earlier farm.  相似文献   

Discussion of de Lange, W. P. and Moon V. G. 2005. Estimating long-term cliff recession rates from shore platform widths. Engineering Geology 80, 292–301     

Wayne Stephenson   《Engineering Geology》2008,101(3-4):288-291

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Iron isotope fractionation in subterranean estuaries     

Olivier Rouxel  Edward Sholkovitz  Katrina J. Edwards 《Geochimica et cosmochimica acta》2008,72(14):3413-3430

Dissolved Fe concentrations in subterranean estuaries, like their river-seawater counterparts, are strongly controlled by non-conservative behavior during mixing of groundwater and seawater in coastal aquifers. Previous studies at a subterranean estuary of Waquoit Bay on Cape Cod, USA demonstrate extensive precipitation of groundwater-borne dissolved ferrous iron and subsequent accumulation of iron oxides onto subsurface sands. Waquoit Bay is thus an excellent natural laboratory to assess the mechanisms of Fe-isotope fractionation in redox-stratified environments and determine potential Fe-isotope signatures of groundwater sources to coastal seawater. Here, we report Fe isotope compositions of iron-coated sands and porewaters beneath the intertidal zone of Waquoit Bay. The distribution of pore water Fe shows two distinct sources of Fe: one residing in the upward rising plume of Fe-rich groundwater and the second in the salt-wedge zone of pore water. The groundwater source has high Fe(II) concentration consistent with anoxic conditions and yield δ⁵⁶Fe values between 0.3 and −1.3‰. In contrast, sediment porewaters occurring in the mixing zone of the subterranean estuary have very low δ⁵⁶Fe values down to −5‰. These low δ⁵⁶Fe values reflect Fe-redox cycling and result from the preferential retention of heavy Fe-isotopes onto newly formed Fe-oxyhydroxides. Analysis of Fe-oxides precipitated onto subsurface sands in two cores from the subterranean estuary revealed strong δ⁵⁶Fe and Fe concentration gradients over less than 2m, yielding an overall range of δ⁵⁶Fe values between −2 and 1.5‰. The relationship between Fe concentration and δ⁵⁶Fe of Fe-rich sands can be modeled by the progressive precipitation of Fe-oxides along fluid flow through the subterranean estuary. These results demonstrate that large-scale Fe isotope fractionation (up to 5‰) can occur in subterranean estuaries, which could lead to coastal seawater characterized by very low δ⁵⁶Fe values relative to river values.  相似文献   

Toxicity of Santa Barbara seep oil to starfish embryos: Part 2—the growth bioassay     

Paul H. Davis  T. Wayne Schultz  Robert B. Spies 《Marine environmental research》1981,5(4):287-294

The asteroid Patiria miniata was used to develop a static bioassay for various crude oil water-soluble fractions (WSF). The criterion used is the size of 48-h exposed embryos. The reasons for choosing this species and the growth criterion are discussed. Experiments show that the body length of 48-h exposed embryos is inversely proportional to hydrocarbon concentration of the WSF and the time of exposure. It is also shown that the toxicity of the WSF decreases with the age of the preparation and that the first 12 h following fertilisation are most sensitive to the effects of WSF.  相似文献   

Pollock (Pollachius virens) stock structure in the Canadian Maritimes inferred from mark-recapture studies     

Neilson  John D.; Stobo  Wayne T.; Perley  Peter 《ICES Journal of Marine Science》2006,63(4):749-765

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