Lithological controls on biological activity and groundwater chemistry in Quaternary sediments     

Rebecca Bartlett  Simon H. Bottrell  Karen Sinclair  Steve Thornton  Ian D. Fielding  Dave Hatfield 《水文研究》2010,24(6):726-735

Depth profiles of solute chemistry and sulfate isotopic compositions are presented for groundwater and pore water in a sequence of Quaternary glacial outwash sediments. Sand units show evidence for hydraulic connection to the surface and thus modern sources of solutes. Finer‐grained sediments show a general pattern of increasing solute concentrations with depth, with sulfate derived from ancient rainwater and pyrite oxidation in the soil/drift. In these sediments sulfate has undergone bacterial sulfate reduction (BSR) to produce biogenic sulfide. In clay sediments, with d₁₀ ≤ 1·6 µm, high concentrations of sulfate and acetate now co‐exist, implying that BSR is inhibited. The correlation with smaller sediment grain size indicates that this is due to pore size exclusion of the sulfate reducing bacteria. Mechanical restriction of microbial function thus provides a fundamental limitation on microbial respiration in buried clay‐rich sediments, which acts as a control on the chemical evolution of their pore waters. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Holocene climate and glacial history of the northeastern Antarctic Peninsula: the marine sedimentary record from a long SHALDRIL core     

Bradley R. Michalchuk  John B. Anderson  Julia S. Wellner  Patricia L. Manley  Wojciech Majewski  Steve Bohaty 《Quaternary Science Reviews》2009,28(27-28):3049-3065

A high-resolution record of Holocene deglacial and climate history was obtained from a 77 m sediment core from the Firth of Tay, Antarctic Peninsula, as part of the SHALDRIL initiative. This study provides a detailed sedimentological record of Holocene paleoclimate and glacial advance and retreat from the eastern side of the peninsula. A robust chronostratigraphy was derived from thirty-three radiocarbon dates on carbonate material. This chronostratigraphic framework was used to establish the timing of glacial and climate events derived from multiple proxies including: magnetic susceptibility, electric resistivity, porosity, ice-rafted debris content, organic carbon content, nitrogen content, biogenic silica content, and diatom and foraminiferal assemblages. The core bottomed-out in a stiff diamicton interpreted as till. Gravelly and sandy mud above the till is interpreted as proximal glaciomarine sediment that represents decoupling of the glacier from the seafloor circa 9400 cal. yr BP and its subsequent landward retreat. This was approximately 5000 yr later than in the Bransfield Basin and South Shetland Islands, on the western side of the peninsula. The Firth of Tay core site remained in a proximal glaciomarine setting until 8300 cal. yr BP, at which time significant glacial retreat took place. Deposition of diatomaceous glaciomarine sediments after 8300 cal. yr BP indicates that an ice shelf has not existed in the area since this time.The onset of seasonally open marine conditions between 7800 and 6000 cal. yr BP followed the deglacial period and is interpreted as the mid-Holocene Climatic Optimum. Open marine conditions lasted until present, with a minor cooling having occurred between 6000 and 4500 cal. yr BP and a period of minor glacial retreat and/or decreased sea ice coverage between 4500 and 3500 cal. yr BP. Finally, climatic cooling and variable sea ice cover occurred from 3500 cal. yr BP to near present and it is interpreted as being part of the Neoglacial. The onset of the Neoglacial appears to have occurred earlier in the Firth of Tay than on the western side of the Antarctic Peninsula. The Medieval Warm Period and Little Ice Age were not pronounced in the Firth of Tay. The breadth and synchroneity of the rapid regional warming and glacial retreat observed in the Antarctic Peninsula during the last century appear to be unprecedented during the Holocene epoch.  相似文献   

Interpreting characteristic drainage timescale variability across Kilombero Valley,Tanzania   总被引：1，自引：0，他引：1       下载免费PDF全文

Steve W. Lyon  Alexander Koutsouris  Friedemann Scheibler  Jerker Jarsjö  Rene Mbanguka  Madaka Tumbo  Keven K. Robert  Asha N. Sharma  Ype van der Velde 《水文研究》2015,29(8):1912-1924

We explore seasonal variability and spatiotemporal patterns in characteristic drainage timescale (K) estimated from river discharge records across the Kilombero Valley in central Tanzania. K values were determined using streamflow recession analysis with a Brutsaert–Nieber solution to the linearized Boussinesq equation. Estimated K values were variable, comparing between wet and dry seasons for the relatively small catchments draining upland positions. For the larger catchments draining through valley bottoms, K values were typically longer and more consistent across seasons. Variations in K were compared with long‐term averaged, Moderate‐resolution Imaging Spectroradiometer‐derived monthly evapotranspiration. Although the variations in K were potentially related to evapotranspiration, the influence of data quality and analysis procedure could not be discounted. As such, even though recession analysis offers a potential approach to explore aquifer release timescales and thereby gain insight to a region's hydrology to inform water resources management, care must be taken when interpreting spatiotemporal shifts in K in connection with process representation in regions like the Kilombero Valley. © 2014 The Authors. Hydrological Processes published by John Wiley & Sons Ltd.  相似文献   

Geographically weighted methods and their use in network re-designs for environmental monitoring   总被引：3，自引：3，他引：0  

Paul Harris  Annemarie Clarke  Steve Juggins  Chris Brunsdon  Martin Charlton 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(7):1869-1887

Given an initial spatial sampling campaign, it is often of importance to conduct a second, more targeted campaign based on the properties of the first. Here a network re-design modifies the first one by adding and/or removing sites so that maximum information is preserved. Commonly, this optimisation is constrained by limited sampling funds and a reduced sample network is sought. To this extent, we demonstrate the use of geographically weighted methods combined with a location-allocation algorithm, as a means to design a second-phase sampling campaign in univariate, bivariate and multivariate contexts. As a case study, we use a freshwater chemistry data set covering much of Great Britain. Applying the two-stage procedure enables the optimal identification of a pre-specified number of sites, providing maximum spatial and univariate/bivariate/multivariate water chemistry information for the second campaign. Network re-designs that account for the buffering capacity of a freshwater site to acidification are also conducted. To complement the use of basic methods, robust alternatives are used to reduce the effect of anomalous observations on the re-designs. Our non-stationary re-design framework is general and provides a relatively simple and a viable alternative to geostatistical re-design procedures that are commonly adopted. Particularly in the multivariate case, it represents an important methodological advance.  相似文献   

中国-巴基斯坦喀喇昆仑公路Ghulkin冰川百年进退变化     

廖丽萍  朱颖彦  杨志全  Muhammad Waseem  Steve Zou  陈济丁  王云  叶成银  张学进 《冰川冻土》2013,35(6):1391-1399

巴基斯坦喀喇昆仑山的Ghulkin冰川是距离中国-巴基斯坦喀喇昆仑公路最近的典型冰川之一,其冰川的进退变化影响着喀喇昆仑公路改建工程的线路设计与工程施工.为了追溯Ghulkin冰川的活动历史和查明近期进退变化,对过去200 a的相关文献和记录进行统计分析,并开展了2008-2011年野外定点观测,总结与分析了Ghulkin冰川冰舌的活动历史与近期变化.研究表明：Ghulkin冰川在1885-1980年近百年间经历了3次前进和3次后退,在此期间冰川波动了625 m;1913-1925年冰川处于显著的前进状态,1966-1978年冰川有小段距离的前进;2008-2011年K676+660处泥石流沟道逐年抬升,2011年南坡冰川融水由K676+660改道至K676+450;2010年的南坡冰舌较1994年后退了300余米,2011年的南坡冰舌较2010年后退了15.066 m,可见在2010-2011年期间冰川处于局部短期后退状态. 中巴公路冰川泥石流等灾害不但受区域气候的影响,而且还受冰川变化的影响.未来气候变暖将会导致冰川的强烈消融和后退,冰川融水携带大量冰碛体,形成大型的冰川泥石流,对公路的安全运营造成严重威胁.  相似文献   

Probabilistic Simulation of Remediation at a Site Contaminated by Trichloroethylene     

Hailian Liang  Ronald W. Falta  James K. Henderson  Steve Shoemaker 《Ground Water Monitoring & Remediation》2012,32(1):131-141

A new probabilistic remediation simulation package, PREMChlor, was used to simulate the effect of contaminant source and plume remediation at a site contaminated by trichloroethylene (TCE). First, the PREMChlor model was calibrated to the plume using a deterministic approach to represent the site conditions prior to remediation activities, which occurred in 1999. The calibrated model was then used in a probabilistic mode to conduct a simulation of the effects of field source and plume remediation activities during the period after 1999. This probabilistic simulation considers uncertainties in seven key parameters: the initial source mass and concentration, the relationship between source mass removal and source concentration, the effectiveness of the source remediation, the groundwater velocity, the background plume degradation rate, and the plume treatment effectiveness. The simulation results compare favorably with the observed data collected after 1999, and show the influence of the remediation efforts on the plume.  相似文献   

Recognition of down-valley translation in tidally influenced meandering fluvial deposits,Athabasca Oil Sands (Cretaceous), Alberta,Canada     

Milovan Fustic  Stephen M. Hubbard  Ron Spencer  Derald G. Smith  Dale A. Leckie  Barry Bennett  Steve Larter 《Marine and Petroleum Geology》2012,29(1):219-232

The vast Athabasca Oil Sands of Alberta, Canada has an estimated resource of more than 1.7 trillion barrels of bitumen in-place, the majority of which is hosted in the Lower Cretaceous McMurray Formation. Despite its economical significance the depositional environment of the formation, and particularly the middle part that is the primary reservoir in most areas, is still a matter of considerable debate. These strata of interest are widely known to comprise fluvial and estuarine point bar deposits that were subject to varying degrees of marine influence. The orientation of point bar strata from the formation is tabulated and the majority is observed to dip paleo-basinward, to the north. This observation has proven difficult to explain by geologists attempting to build predictive models for the formation over the last two decades. However, the basinward-dipping point bar strata can be attributed to widespread down-valley translation of point bars in confined north-south oriented valleys, which have previously been delineated in the region. Differentiating the deposits of lateral point bar migration and down-valley translation in the rock record is not possible at the facies scale, and thus translated point bars have not been previously recognized or interpreted in the rock record, despite their prevalence in numerous modern fluvial valley systems. Their identification in the McMurray Formation has important implications for the delineation and development of Canada’s economically significant oil sands resources.  相似文献   

The effect of critical pH on virus fate and transport in saturated porous medium   总被引：1，自引：0，他引：1  

Guan H  Schulze-Makuch D  Schaffer S  Pillai SD 《Ground water》2003,41(5):701-708

Several viral transport experiments were conducted in a model aquifer 1 m long, using bacteriophages MS2 and phiX174 at various pH (4.6 to 8.3) conditions, to increase our understanding of virus behavior in ground water. The results indicate the existence of a critical pH at which the virus behavior changes abruptly. This is supported by data from field and batch experiments. The critical pH is determined to be 0.5 unit below the highest isoelectric point of the virus and porous medium. When water pH is below the critical pH, the virus has an opposite charge to at least one component of the porous medium, and is almost completely and irreversibly removed from the water. This suggests that electrostatic attraction at a subcritical water pH condition is an important factor controlling virus attenuation in ground water. The concept of critical pH can assist in the design of geologic barriers for preventing viral contamination in ground water.  相似文献   

On the Dynamics of the Jovian Ionosphere and Thermosphere: II. The Measurement of H₃ Vibrational Temperature, Column Density, and Total Emission     

Tom Stallard  Steve Miller  George MillwardRobert D. Joseph 《Icarus》2002,156(2):498-514

We present the first reported measurements of the intensity of a “hotband” transition for the H₃⁺ molecular ion in the northern auroral/polar region of Jupiter. This transition is identified as the R(3, 4⁺) line of the (2v₂(l=0)→v₂) hotband, with a wavelength of 3.94895 μm. This is the first time such a transition has been measured outside the laboratory, and the wavelength as measured on Jupiter is within the experimental accuracy of the lab measurement. This detection makes it possible to investigate H₃⁺ transitions that simultaneously originate from different vibrational levels. We use the intensity ratio between this line and the Q(1, 0⁻) fundamental transition to derive effective vibrational temperatures, column densities, and total emission parameters as a function of position across the auroral/polar region. Effective temperatures range from ∼900 to ∼1250 K; an increase in average temperature during our observing run of ∼100 K is noted. The derived temperatures are toward the high end or in excess of the auroral temperature range that has been reported in the literature to date. The relationship among emission intensity, temperature, and density is shown to be complex. This may reflect the nonthermalization of the vibrational levels at the gas densities prevailing in the jovian thermosphere. An alternative analysis allowing for this effect is presented. But this approach requires thermospheric temperatures to be ∼1500 K at the level that the majority of H₃⁺ is being produced, higher than has previously been proposed.  相似文献   

The SCUBA Half Degree Extragalactic Survey – IV. Radio–mm–FIR photometric redshifts     

Itziar Aretxaga  David H. Hughes  Kristen Coppin  Angela M. J. Mortier  Jeff Wagg  James S. Dunlop  Edward L. Chapin  Stephen A. Eales  Enrique Gaztañaga  Mark Halpern  Rob J. Ivison  Eelco van Kampen  Douglas Scott  Stephen Serjeant  Ian Smail  Thomas Babbedge  rew J. Benson  Scott Chapman  David L. Clements  Loretta Dunne  Simon Dye  Duncan Farrah  Matt J. Jarvis  Robert G. Mann  Alexandra Pope  Robert Priddey  Steve Rawlings  Marc Seigar  Laura Silva  Chris Simpson  Mattia Vaccari 《Monthly notices of the Royal Astronomical Society》2007,379(4):1571-1588

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