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681.
682.
Rachel Bynoe Nick M. Ashton Tim Grimmer Peter Hoare Joanne Leonard Simon G. Lewis Darren Nicholas Simon Parfitt 《第四纪科学杂志》2021,36(2):191-210
Recent archaeological discoveries from exposures of the Cromer Forest-bed Formation at Happisburgh, UK, have radically changed interpretations of the nature and timing of early hominin occupation of northern latitudes, but this in situ archaeology is only one part of the picture. Surface finds of Pleistocene mammalian remains have been found along this coastline for centuries, with stone tools adding to this record over the past 7 years. The ex situ nature of these finds, however, means they are often seen as limited in the information they can provide. This work contributes to a growing body of research from a range of landscape and environmental contexts that seeks to demonstrate the value and importance of these ex situ assemblages. Here the focus is on Palaeolithic flint artefacts and Pleistocene mammalian remains recovered by a group of local collectors through systematic, GPS-recorded beach collection from 2013 to 2017, and their use in developing a methodology for working with ex situ Palaeolithic finds in coastal locations. The results demonstrate significant patterning that identifies unexplored exposures both onshore and offshore, considerably expanding the known extent of deposits and facilitating new insights into the wider archaeological landscape associated with the earliest occupation of northern Europe. 相似文献
683.
684.
Calcareous fens are minerotrophic peatlands with very high species diversity, and maintenance of the water table is assumed to be a key contributor to this diversity. However, this assumption is based on limited study of fen water table dynamics. Here we monitor water table fluctuation in distributed locations across three calcareous fens differing in hydrogeomorphic setting for three growing seasons. Water table position was extremely variable with absolute ranges of 89, > 100, and > 118 cm in the Riparian, Trough and Basin Fens, respectively, and was controlled by landscape position and weather variability. Areas adjacent to a second‐order stream experienced the least water table fluctuation, while the Basin Fen, at > 75 m from a surface water connection, was very prone to year‐to‐year precipitation differences. Mean and median water table values were found to be poor indicators of biologically relevant hydroperiods. We introduce the term ‘duration of initial growing season saturation’ as a potentially more useful statistic to relate to plant species distribution. Across the studied fens, this duration ranged from 1 to 14 weeks from the start of the growing season. The water table resided below the ground surface for between 0 and 22 weeks of the growing season across the calcareous fens and study period. These findings impart great differences in the development of oxidized rooting depths. Our results demonstrate that there is much more variation in calcareous fen hydrology than previously reported, and this variability has important implications for fen vegetation patterning and management. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
685.
Colin J. Whitfield Julian Aherne John J. Gibson Tim A. Seabert Shaun A. Watmough 《水文研究》2010,24(15):2143-2155
Spatial and temporal variability in surface water chemistry, organic soil chemistry and hydrologic indicators were investigated at three poor‐fen complexes in two boreal catchments in Northern Alberta to provide insight into the dominant controls on surface water chemistry. Improved understanding of these controls is required to enable prediction of runoff chemistry in the region under changing atmospheric deposition conditions. Surface water chemistry exhibited considerable variability; within each fen conductivity, dissolved organic carbon (DOC), and Cl− tended to decrease and pH tended to increase with increasing distance from the lake edge. Variations in evaporative isotopic enrichment in 2H and 18O, expressed as deuterium excess, were used to distinguish between throughflow waters and those that were more evaporatively enriched. Throughflow surface waters were more acidic primarily due to higher concentrations of DOC and NO3−. Exchangeable base saturation and pH of organic soils were strongly related to surface water chemistry at two of the fen complexes, demonstrating the capacity for cation exchange to influence surface water chemistry. Fen surface water concentrations of most elements and DOC increased during the summer period (between June and August), while pH of water decreased. Evaporative concentration of the surface waters was a dominant driver, with surface water temperature increasing at both catchments. Localized groundwater discharge was an important contributor of base cations to the fens, while the organic soils are sinks for atmospherically deposited SO42−, N and Cl−. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
686.
Robert Haining Jane Law Ravi Maheswaran Tim Pearson Paul Brindley 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(5):501-509
Bayesian modelling of health risks in relation to environmental exposures offers advantages over conventional (non-Bayesian)
modelling approaches. We report an example using research into whether, after controlling for different confounders, air pollution
(NOx) has a significant effect on coronary heart disease mortality, estimating the relative risk associated with different levels
of exposure. We use small area data from Sheffield, England and describe how the data were assembled. We compare the results
obtained using a generalized (Poisson) log-linear model with adjustment for overdispersion, with the results obtained using
a hierarchical (Poisson) log-linear model with spatial random effects. Both classes of models were fitted using a Bayesian
approach. Including spatial random effects models both overdispersion and spatial autocorrelation effects arising as a result
of analysing data from small contiguous areas. The first modelling framework has been widely used, while the second provides
a more rigorous model for hypothesis testing and risk estimation when data refer to small areas. When the models are fitted
controlling only for the age and sex of the populations, the generalized log-linear model shows NOx effects are significant at all levels, whereas the hierarchical log-linear model with spatial random effects shows significant
effects only at higher levels. We then adjust for deprivation and smoking prevalence. Uncertainty in the estimates of smoking
prevalence, arising because the data are based on samples, was accounted for through errors-in-variables modelling. NOx effects apparently are significant at the two highest levels according to both modelling frameworks.
相似文献
Paul BrindleyEmail: |
687.
Ardeshir Dehmoobed Sharif-abadi Tim Grain Joseph 《Geotechnical and Geological Engineering》2010,28(4):471-481
Strain softening of oil sand under dynamic loading from large mining equipment inhibits the ability of the equipment to function
at optimal design performance. This paper looks at the findings of dynamic plate load tests, which effectively mimick the
loading and unloading action of a shovel track pad. A pseudo-elastic model was proposed based on the results of the dynamic
plate load testing to predict the deformation of oil sand under cyclic loading. Both field and laboratory cyclic plate load
tests were performed on oil sand materials. The field tests were performed with different plate sizes, or footprints. The
load was normalized based on the pressure stiffness concept in units of pressure per unit deformation. FLAC was used to model
the field plate load test deformation with the elastic concept. The laboratory tests were performed at room temperature with
more control on the load, loading rate, and cycles than possible during the field testing. Tests were conducted using a circular
plate of 14.9 cm diameter, at stress magnitudes of 200, 400, 500 and 600 kPa. The plate load tests were conducted for varying
loads, holding, and relaxation times of 0, 2, 5 and 10 min respectively for each magnitude of stress. The outcome of laboratory
plate load tests show that after frequent cycles, the pressure stiffness (ratio of stress to deformation) converges on a plateau
value of 8 kPa/mm. The proposed approach can be used to evaluate oil sands ground performance, enhancing the prediction process
for ground deformation under the operation of ultra-class mining equipment. 相似文献
688.
Stephan Schulz Rike Becker Juan Carlos Richard-Cerda Muhammad Usman Tim aus der Beek Ralf Merz Christoph Schüth 《水文研究》2021,35(3):e14077
Information on water balance components such as evapotranspiration and groundwater recharge are crucial for water management. Due to differences in physical conditions, but also due to limited budgets, there is not one universal best practice, but a wide range of different methods with specific advantages and disadvantages. In this study, we propose an approach to quantify actual evapotranspiration, groundwater recharge and water inflow, i.e. precipitation and irrigation, that considers the specific conditions of irrigated agriculture in warm, arid environments. This approach does not require direct measurements of precipitation or irrigation quantities and is therefore suitable for sites with an uncertain data basis. For this purpose, we combine soil moisture and energy balance monitoring, remote sensing data analysis and numerical modelling using Hydrus. Energy balance data and routine weather data serve to estimate ET0. Surface reflectance data from satellite images (Sentinel-2) are used to derive leaf area indices, which help to partition ET0 into energy limited evaporation and transpiration. Subsequently, first approximations of water inflow are derived based on observed soil moisture changes. These inflow estimates are used in a series of forward simulations that produce initial estimates of drainage and ETact, which in turn help improve the estimate of water inflow. Finally, the improved inflow estimates are incorporated into the model and then a parameter optimization is performed using the observed soil moisture as the reference figure. Forward simulations with calibrated soil parameters result in final estimates for ETact and groundwater recharge. The presented method is applied to an agricultural test site with a crop rotation of cotton and wheat in Punjab, Pakistan. The final model results, with an RMSE of 2.2% in volumetric water content, suggest a cumulative ETact and groundwater recharge of 769 and 297 mm over a period of 281 days, respectively. The total estimated water inflow accounts for 946 mm, of which 77% originates from irrigation. 相似文献
689.
Storm track sensitivity to sea surface temperature resolution in a regional atmosphere model 总被引:1,自引:1,他引:0
Tim Woollings Brian Hoskins Mike Blackburn David Hassell Kevin Hodges 《Climate Dynamics》2010,35(2-3):341-353
A high resolution regional atmosphere model is used to investigate the sensitivity of the North Atlantic storm track to the spatial and temporal resolution of the sea surface temperature (SST) data used as a lower boundary condition. The model is run over an unusually large domain covering all of the North Atlantic and Europe, and is shown to produce a very good simulation of the observed storm track structure. The model is forced at the lateral boundaries with 15–20 years of data from the ERA-40 reanalysis, and at the lower boundary by SST data of differing resolution. The impacts of increasing spatial and temporal resolution are assessed separately, and in both cases increasing the resolution leads to subtle, but significant changes in the storm track. In some, but not all cases these changes act to reduce the small storm track biases seen in the model when it is forced with low-resolution SSTs. In addition there are several clear mesoscale responses to increased spatial SST resolution, with surface heat fluxes and convective precipitation increasing by 10–20% along the Gulf Stream SST gradient. 相似文献
690.
耦合模式FGOALS_s 模拟的亚澳季风年际变率及ENSO 总被引:10,自引:7,他引:3
本文评估了中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室 (LASG/IAP) 新一代耦合气候模式FGOALS_s对亚澳季风和ENSO的模拟。结果表明, FGOALS_s可以模拟出亚澳季风的主要气候态特征。FGOALS_s模拟的ENSO事件振幅为观测值的70%, 同时它合理再现了ENSO周期的非规则性。FGOALS_s可以定性模拟出ENSO的主要空间特征。当赤道东太平洋SST升高时, 印度洋和西太平洋海表面气压升高, 而东太平洋海表面气压降低。FGOALS_s的主要缺陷在于模拟的ENSO峰值多出现在春季和夏季。与ENSO振幅偏小相反, FGOALS_s模拟的亚澳季风年际变率振幅大于观测。但是观测中亚澳季风年际变率与ENSO暖位相的显著负相关关系, 在模式中没有得到合理再现, 原因部分可归之于耦合模式在ENSO锁相模拟上的缺陷。由于模式模拟的ENSO峰值出现在北半球春季和夏季, Walker环流异常下沉支移动到西北太平洋, 其激发出的异常反气旋位置较之观测要偏东, 导致印度季风降水和El Niño的负相关关系不显著; 在北半球冬季, 由于模式中的赤道东太平洋SST暖异常较弱, 亚澳季风响应也偏弱。此外, 由于赤道东太平洋SST异常向西伸展, 观测中位于澳洲季风区的辐散中心向西偏移, 最终导致模式中澳洲季风降水与ENSO的负相关同样不显著。 相似文献