Chironomid-based water depth reconstructions: an independent evaluation of site-specific and local inference models   总被引：1，自引：1，他引：0  

Stefan Engels  Les C. Cwynar  Andrew B. H. Rees  Bryan N. Shuman 《Journal of Paleolimnology》2012,48(4):693-709

Water depth is an important environmental variable that explains a significant portion of the variation in the chironomid fauna of shallow lakes. We developed site-specific and local chironomid water-depth inference models using 26 and 104 surface-sediment samples, respectively, from seven kettlehole lakes in the Plymouth Aquifer, southeast Massachusetts, USA. Our site-specific model spans a depth gradient of 5.6?m, has an $ {\text{r}}_{\text{jack}}^{2} $ of 0.90, root mean square error of prediction (RMSEP) of 0.5?m and maximum bias of 0.7?m. Our local model has a depth gradient of 11.7?m, an $ {\text{r}}_{\text{jack}}^{2} $ of 0.71, RMSEP of 1.6?m and maximum bias of 2.9?m. Principal coordinates of neighbourhood matrices (PCNM) analysis showed that there is no influence of spatial autocorrelation on the site-specific model, but PCNM variables explained a significant amount of variance (4.8%) in the local model. This variance, however, is unique from the variance explained by water depth. We applied the inference models to a Holocene chironomid record from Crooked Pond, a site for which multiple, independent palaeohydrological reconstructions are available. The chironomid-based reconstructions are remarkably similar and show stable water depths of ~5?m, interrupted by a 2-m decrease between 4,200 and 3,200?cal a BP. Sedimentological evidence of water level fluctuations at Crooked Pond, obtained using the so-called Digerfeldt approach, also shows a drop in water depths around that time. The period of reconstructed lower water levels coincides with the abrupt decline in moisture-dependent hemlock in this region, providing further evidence for this major palaeohydrological event. The site-specific model has the best performance statistics, but the high percent abundance of fossil taxa from the long core that are absent or rare in the training set makes the site-specific reconstruction unreliable for the period before 4,400?cal a BP. The fossil taxa are well represented in the local model, making it the preferred inference model. The strong similarity between the chironomid-based reconstructions and the independent palaeohydrological records highlights the potential for using chironomid-based inference models to determine past lake depths at sites where temperature was not an influencing factor.  相似文献   

Framework for soil suitability evaluation for sewage effluent renovation     

Steven?CarrollEmail author  Ashantha?Goonetilleke  Les?Dawes 《Environmental Geology》2004,46(2):195-208

Current methods of establishing suitable locations for onsite wastewater treatment systems (OWTS) are inadequate, particularly in light of the numerous cases of onsite system failure and the resulting adverse consequences. The development of a soil suitability framework for assessing soil suitability for OWTS allows a more practical means of assessment. The use of multivariate statistical analysis techniques, including Principal Component Analysis (PCA) and multi-criteria decision aids of PROMETHEE and GAIA, enabled the identification of suitable soils for effluent renovation. The outcome of the multivariate analysis, together with soil permeability and drainage characteristics permitted the establishment of a framework for assessing soil suitability based on three main soil functions: (1) the ability of the soil to provide suitable effluent renovation, (2) the permeability of the soil, and (3) the soils drainage characteristics. The developed framework was subsequently applied to the research area, Gold Coast, Queensland, Australia, and the use of standard scoring functions were utilised to provide a scoring system to signify which soils were more suitable for effluent renovation processes. From the assessment, it was found that Chromosol and Kurosol soils provided the highest level of effluent renovation, closely followed by Ferrosol and Dermosol, Kandosol and Rudosol soil types. Tennosol and Podosol soil types were found to have a significantly lower suitability, with Hydrosol soils proving the least suitable for renovating effluent from OWTS.  相似文献   

A northwest North American training set: distribution of freshwater midges in relation to air temperature and lake depth     

Erin M. Barley  Ian R. Walker  Joshua Kurek  Les C. Cwynar  Rolf W. Mathewes  Konrad Gajewski  Bruce P. Finney 《Journal of Paleolimnology》2006,36(3):295-314

Freshwater midges, consisting of Chironomidae, Chaoboridae and Ceratopogonidae, were assessed as a biological proxy for palaeoclimate in eastern Beringia. The northwest North American training set consists of midge assemblages and data for 17 environmental variables collected from 145 lakes in Alaska, British Columbia, Yukon, Northwest Territories, and the Canadian Arctic Islands. Canonical correspondence analyses (CCA) revealed that mean July air temperature, lake depth, arctic tundra vegetation, alpine tundra vegetation, pH, dissolved organic carbon, lichen woodland vegetation and surface area contributed significantly to explaining midge distribution. Weighted averaging partial least squares (WA-PLS) was used to develop midge inference models for mean July air temperature (r _boot² = 0.818, RMSEP = 1.46°C), and transformed depth (ln (x+1); r _boot² = 0.38, and RMSEP = 0.58).  相似文献   

In situ U-series dating by laser-ablation multi-collector ICPMS: new prospects for Quaternary geochronology   总被引：2，自引：0，他引：2  

Stephen M. Eggins  Rainer Grün  Malcolm T. McCulloch  Alistair W.G. Pike  John Chappell  Les Kinsley  Graham Mortimer  Michael Shelley  Colin V. Murray-Wallace  Christoph Sptl  Lois Taylor 《Quaternary Science Reviews》2005,24(23-24):2523-2538

The capabilities and potential applications of in situ dating of Quaternary materials using laser ablation-MC-ICPMS are explored. ²³⁴U/²³⁸U and ²³⁰Th/²³⁴U can be measured with precision sufficient for dating at a spatial resolution of 100 μm or better in samples that contain as a little as 1 ppm uranium. Moreover, U and Th concentrations and U-series isotope ratios can be continuously profiled to determine changes in age that occur with sample growth (e.g. in speleothems). These capabilities additionally permit the dating of bones, teeth and possibly molluscs, which are subject to post-mortem open-system behaviour of U-series isotopes, and can be employed to elucidate processes of U-series migration during weathering and diagenesis. A drawback of laser ablation-MC-ICPMS is that it cannot in general provide U-series age estimates with the high precision and accuracy of conventional TIMS or solution MC-ICPMS methods. However, sample preparation is straightforward, the amount of sample consumed negligible, and it can be used to rapidly characterise or screen and select samples from which more precise and accurate dates can be obtained using conventional methods. Given further instrumental developments and the establishment of suitable matrix-matched standards for carbonates and other materials, we foresee that laser ablation-MC-ICPMS will play an increasingly important role in Quaternary dating research.  相似文献   

Some observations on the chemical weathering of the Dartmoor granite     

Andrew G. Williams  Les Ternan  Martin Kent 《地球表面变化过程与地形》1986,11(5):557-574

The majority of geomorphological papers about Dartmoor have been essentially speculative, particularly when discussing weathering processes and the evolution of the Dartmoor landscape. In contrast, this article presents a synthesis of several experimental investigations aimed at studying the chemical weathering of Dartmoor granite through the systematic analysis of soil and water samples. This involved the computation of a geochemical budget to determine the amount of erosion in the catchment, as well as more detailed mineralogical investigations within a soil profile. The annual output of solutes due to weathering was 116 kg ha^?1 a^?1 of which the majority was silica (93 kg ha^?1 a^?1). From an examination of the soil mineralogy, it was calculated that these solutes were derived from the dissolution of approximately 200 kg ha^?1 a^?1 plagioclase, 90 kg ha^?1 a^?1 biotite, and 40 kg ha^?1 a^?1 orthoclase. As well as the weathering of granite, there was also the production of kaolinite (150 kg ha^?1 a^?1) and gibbsite (0.02 kg ha^?1 a^?1). Analysis of the soil water chemistry confirmed that kaolinite was the stable mineral phase in the regolith, although in areas where interflow was the dominant mode of water movement, the solute composition was in equilibrium with both kaolinite and gibbsite. Examination of the clay mineralogy confirmed these results. The microtexture of quartz grains was examined by the scanning electron microscope as another means of investigating the hydrochemical environment in the soil. Silica was found precipitated on all the grains examined but the maximum amount occurred in the Bs horizon. This evidence showed that, firstly, the dissolution of aluminosilicate minerals is greater than that calculated by the chemical budget and, secondly, that models of granite weathering must take localized weathering in the soil profile into account. The final part of the paper highlights the limitations of calculating denudation rates for an entire catchment and stresses the need to consider weathering as a highly localized phenomenon, particularly where there are high volumes of interflow at hill crest sites. Observations on granite decomposition in the future should be quantitative in approach and be related to the local site conditions.  相似文献   

Fractal dimension of faults network in the upper silesian coal basin (Poland): Preliminary studies     

Adam Idziak  Lesław Teper 《Pure and Applied Geophysics》1996,147(2):239-247

Fractal analysis of faults network, tremor foci spatial distribution as well as the Gutenberg-Richter relationship could further explain whether the biggest seismic events are connected with recent tectonic activity. Fractality of fault systems geometry, as a first step of the analysis, was tested fro a part of the USCB embodying the main structural units. The cluster analysis and the box counting methods were employed.The calculated fractal dimension of fault network was 1.98 for the whole area yet for considered structural units it was close to 1.6. The results point to similarity of studied fault pattern to river network. Faults within selected tectonic units make separate sets which have a distinct geometry and origin. The value of 1.6 is an upper limit to the fracture geometry of rocks that can be explained on the basis of Griffith energy balance concept.  相似文献   

Coexistence or contradiction? GM crops versus alternative agricultures in Europe     

Les Levidow  Karin Boschert 《Geoforum》2008,39(1):174-190

Agricultural biotechnology (agbiotech) has intersected with a wider debate about ‘sustainable agriculture’, especially in Europe. Agbiotech was initially promoted as an alternative which would avoid or remedy past problems of intensive agriculture, but such claims were soon challenged. Agbiotech has extended the dominant agri-industrial paradigm, while critics have counterposed alternatives corresponding to an agrarian-based rural development paradigm. Amid controversy over environmental and health risks in the late 1990s, an extra issue emerged − the prospect that genetically modified (GM) material would become inadvertently mixed with non-GM crops. In response the European Commission developed a policy framework for ‘coexistence’ between GM, conventional and organic crops. This policy has aimed to ensure that farmers can freely choose among different production systems, which would develop side by side, yet specific proposals for coexistence rules favour some choices over others. Such rules have been contested according to different policy agendas, each promoting their model of future agriculture. Moreover, a Europe-wide network of regional authorities has promoted ‘GM-free zones’ as a territorial brand for green, localised, high-quality agri-food production, whose diverse qualities depend upon symbolic, immaterial characteristics. This alternative has been counterposed to the agri-industrial production of global commodities - symbolised by the European Union, especially its product authorisation procedure for the internal market. ‘Coexistence’ policy was intended to mediate policy conflicts over GM crops, yet it has become another arena for contending agricultural systems, which may not so readily co-exist in practice. Wherever an agrarian-based rural development paradigm gains local support, its alternative agricultures are in contradiction rather than coexistence with GM crops.  相似文献   

Surface complexation modelling of Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II) adsorption onto kaolinite     

Xueyuan Gu  Les J. Evans 《Geochimica et cosmochimica acta》2008,72(2):267-276

Proton binding constants for the edge and basal surface sites of kaolinite were determined by batch titration experiments at 25 °C in the presence of 0.1 M, 0.01 M and 0.001 M solutions of NaNO₃ and in the pH range 3-9. By optimizing the results of the titration experiments, the ratio of the edge sites to the basal surface sites was found to be 6:1. The adsorption of Cd(II), Cu(II), Ni(II), Zn(II) and Pb(II) onto kaolinite suspensions was investigated using batch adsorption experiments and results suggested that in the lower pH range the metallic cations were bound through non-specific ion exchange reactions on the permanently charged basal surface sites (X⁻). Adsorption on these sites was greatly affected by ionic strength. With increasing pH, the variable charged edge sites (SOH) became the major adsorption sites and inner-sphere specifically adsorbed monodentate complexes were believed to be formed. The effect of ionic strength on the extent of adsorption of the metals on the variable charged edge sites was much less than those on the permanently charged sites. Two binding constants, log K_(X2Me) and log K_(SOMe), were calculated by optimizing these constants in the computer program FITEQL. A model combining non-specific ion exchange reactions and inner-sphere specific surface complexations was developed to predict the adsorption of heavy metals onto kaolinite in the studied pH range. Linear free energy relationships were found between the edge site binding constants and the first hydrolysis constants of the metals.  相似文献   

The Global Stratotype Section and Point （GSSP） for the base of the Holocene Series/Epoch （Quaternary System/Period） in the NGRIP ice core   总被引：4，自引：0，他引：4  

Mike Walker  ;Sigfus Johnsen  ;Sune Olander Rasmussen  ;Jorgen-Peder Steffensen  ;Trevor Popp  ;Philip Gibbard  ;Wim Hoek  ;John Lowe  ;John Andrews  ;Svante Bjorck  ;Les Cwynar  ;Konrad Hughen  ;Peter Kershaw  ;Bernd Kromer  ;Thomas Litt  ;David J. Lowe  ;Takeshi Nakagawa  ;Rewi Newnham  ;Jakob Schwander 《《幕》》2008,31(2):264-267

The Greenland ice core from NorthGRIP （NGRIP） contains a proxy climate record across the Pleistocene-Holocene boundary of unprecedented clarity and resolution. Analysis of an array of physical and chemical parameters within the ice enables the base of the Holocene, as reflected in the first signs of climatic warming at the end of the Younger Dryas/Greenland Stadial 1 cold phase, to be located with a high degree of precision.  相似文献   

Stability studies of surficial sediments in the Wilmington-Lindenkohl Canyons area,eastern U.S. margin     

Gideon Almagor  Richard H. Bennett  Bonnie A. Mc Gregor  Les E. Shephard 《Geo-Marine Letters》1982,2(3-4):129-134

Stability analysis, based on infinite slope analysis and geotechnical data from a suite of 34 cores collected from the continental slope between Wilmington and Lindenkohl Canyons, indicates that the Quaternary surficial silty clay sediments on gentle slopes are stable; that sediment stability on steeper slopes (14°–19°) is marginal; and that on precipitous slopes (>50°) only a thin veneer of unconsolidated sediments can exist. Small earthquake-induced accelerations or the effects of internal waves can result in slope sediment instabilities.  相似文献