Seepage measurements from Long Lake,Indiana Dunes National Lakeshore     

S. A. Isiorho  F. M. Beeching  P. M. Stewart  R. L. Whitman 《Environmental Geology》1996,28(2):99-105

 Long Lake, located near Lake Michigan within the dune-complexes of Indiana Dunes National Lakeshore, USA, was formed some time during the Pleistocene and Holocene epochs. A surficial aquifer underlies Long Lake, which is either a source or sink for the later. The hydrologic processes in the lakeshore and surrounding environs have been significantly altered during the agricultural, municipal, and industrial development of the region. Limited data suggest that the organisms of Long Lake have elevated levels of several contaminants. This study attempts to quantify seepage within the lake to assess the potential threat to groundwater quality. Seepage measurements and minipiezometric tests were used to determine seepage within the lake. Seepage measurements and minipiezometric tests suggest that water seeps out of Long Lake, thus recharging the groundwater that flows southwest away from the lake. There is a great deal of variability in the seepage rate, with a mean of 11.5×10^–4±11.2×10^–4 m d^–1. The mean seepage rate of 0.3 m yr^–1 for Long Lake is greater than the 0.2 m yr^–1 recharge rate estimated for the drainage basin area. The Long Lake recharge volume of 2.5×10⁵ m³ yr^–1 is approximately 22% of the volume of the lake and is significant when compared to the total surface recharge volume of 4.8×10⁵ m³ yr^–1 to the upper aquifer of the drainage area. There is a potential for contamination of the groundwater system through seepage from the lake from contaminants derived from aerial depositions. Received: 16 August 1995 · Accepted: 18 September 1995  相似文献   

Aggregation Issues in Cognitive Mapping     

Robert M. Kitchin  A. Stewart Fotheringham 《The Professional geographer》1997,49(3):269-280

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An assessment of particulate organic carbon to thorium-234 ratios in the ocean and their impact on the application of Th as a POC flux proxy     

K.O. Buesseler  C.R. Benitez-Nelson  S.B. Moran  A. Burd  M. Charette  J.K. Cochran  L. Coppola  N.S. Fisher  S.W. Fowler  W.D. Gardner  L.D. Guo   . Gustafsson  C. Lamborg  P. Masque  J.C. Miquel  U. Passow  P.H. Santschi  N. Savoye  G. Stewart  T. Trull 《Marine Chemistry》2006,100(3-4):213

Thorium-234 is increasingly used as a tracer of ocean particle flux, primarily as a means to estimate particulate organic carbon export from the surface ocean. This requires determination of both the ²³⁴Th activity distribution (in order to calculate ²³⁴Th fluxes) and an estimate of the C / ²³⁴Th ratio on sinking particles, to empirically derive C fluxes. In reviewing C / ²³⁴Th variability, results obtained using a single sampling method show the most predictable behavior. For example, in most studies that employ in situ pumps to collect size fractionated particles, C / ²³⁴Th either increases or is relatively invariant with increasing particle size (size classes > 1 to 100s μm). Observations also suggest that C / ²³⁴Th decreases with depth and can vary significantly between regions (highest in blooms of large diatoms and highly productive coastal settings). Comparisons of C fluxes derived from ²³⁴Th show good agreement with independent estimates of C flux, including mass balances of C and nutrients over appropriate space and time scales (within factors of 2–3). We recommend sampling for C / ²³⁴Th from a standard depth of 100 m, or at least one depth below the mixed layer using either large volume size fractionated filtration to capture the rarer large particles, or a sediment trap or other device to collect sinking particles. We also recommend collection of multiple ²³⁴Th profiles and C / ²³⁴Th samples during the course of longer observation periods to better sample temporal variations in both ²³⁴Th flux and the characteristic of sinking particles. We are encouraged by new technologies which are optimized to more reliably sample truly settling particles, and expect the utility of this tracer to increase, not just for upper ocean C fluxes but for other elements and processes deeper in the water column.  相似文献   

Seafloor character and sedimentary processes in eastern Long Island Sound and western Block Island Sound     

L. J. Poppe  M. L. DiGiacomo-Cohen  S. M. Smith  H. F. Stewart  N. A. Forfinski 《Geo-Marine Letters》2006,26(2):59-68

Multibeam bathymetric data and seismic-reflection profiles collected in eastern Long Island Sound and western Block Island Sound reveal previously unrecognized glacial features and modern bedforms. Glacial features include an ice-sculptured bedrock surface, a newly identified recessional moraine, exposed glaciolacustrine sediments, and remnants of stagnant-ice-contact deposits. Modern bedforms include fields of transverse sand waves, barchanoid waves, giant scour depressions, and pockmarks. Bedform asymmetry and scour around obstructions indicate that net sediment transport is westward across the northern part of the study area near Fishers Island, and eastward across the southern part near Great Gull Island.  相似文献   

Problems associated with seismic facies analysis of diamicton-dominated,shelf glacigenic sequences     

F. S. Stewart  M. S. Stoker 《Geo-Marine Letters》1990,10(3):151-156

Diamicton-dominated shelf glacigenic sequences are characterized on high-resolution seismic records by a structureless to chaotic acoustic texture, often with abundant hyperbolic (point-source) reflections. Existing depositional models, based primarily on seismic data, have been constructed on the basis that this acoustic signature is indicative of subglacial till. However, borehole data from the UK continental shelf indicate that glaciomarine facies are also present. Thus, while this acoustic character may be indicative of diamicton lithofacies, it should not be taken as a predictive genetic indicator of a specific depositional process.  相似文献   

Source heights of metre wavelength bursts of spectral types I and III     

R. T. Stewart 《Solar physics》1976,50(2):437-445

Direct measurements by the Culgoora radioheliograph of the apparent source heights of type I and type III bursts at the solar limb are described. The average observed height is approximately the same for type I and type III sources. The heights are somewhat larger than previous estimates. After refraction effects are removed the present results give an electron density model for the source region below 3 R with densities on the average between 8 and 10 times the values for corresponding heights in the quiet K-corona.  相似文献   

I/I ratios in Scottish coastal surface sea water: Geographical and temporal responses to changing emissions     

Christoph Schnabel  Valérie Olive  Mariko Atarashi-Andoh  Andrew Dougans  Robert M. Ellam  Stewart Freeman  Colin Maden  Martin Stocker  Hans-Arno Synal  Lukas Wacker  Sheng Xu 《Applied Geochemistry》2007

This work constitutes the first survey of I isotope ratios for Scottish sea water including the first data for the west of Scotland. These data are of importance because of the proximity to the world’s second largest emission source of ¹²⁹I to the sea, the Sellafield nuclear reprocessing plant, because of the increasing importance of the sea to land transfer of ¹²⁹I and also as input data for dose estimates based on this pathway of ¹²⁹I. ¹²⁹I/¹²⁷I ratios in SW Scotland reached 3 × 10⁻⁶ in 2004. No strong variation of I isotope ratios was found from 2003 to 2005 in Scottish sea waters. Iodine isotope ratios increased by about a factor of 6 from 1992 to 2003 in NE Scotland, in agreement with the increase of liquid ¹²⁹I emissions from Sellafield over that time period. It is demonstrated that ¹²⁹I/¹²⁷I ratios agree better than ¹²⁹I concentrations for samples from similar locations taken in very close temporal proximity, indicating that this ratio is more appropriate to interpret than the radionuclide concentration.  相似文献   

Ecological impacts of air pollution from road transport on local vegetation     

Keeley L. Bignal  Mike R. Ashmore  Alistair D. Headley  Kirstin Stewart  Katherina Weigert 《Applied Geochemistry》2007

Motor vehicles emit a cocktail of pollutants and are a major contributor to ground-level air pollution, but little is known regarding the ecological impacts of air pollution from roads on the surrounding vegetation. Data are presented on vegetation at three sites adjacent to two major motorways in the UK, comprising two woodland sites and one blanket bog site. Surveys of oak and beech tree health (at the woodland sites) and species composition (at the blanket bog site) were undertaken along transects away from the motorway.  相似文献   

A study of pore geometry effects on anisotropy in hydraulic permeability using the lattice-Boltzmann method     

M.L. Stewart  A.L. Ward  D.R. Rector 《Advances in water resources》2006

We hypothesize that anisotropy in soil properties arises from pore-scale heterogeneity caused by the alignment of aspherical soil particles. We developed a method to predict the permeability tensor from particle shape and packing structure. Digital geometry maps were created for the pore space in regular cubic and random packs of particles with various aspect ratios using a numerical packing algorithm. The lattice-Boltzmann method was used to simulate saturated flow through these packs, and the effect of particle shape and degree of alignment on the permeability tensor was characterized. Results show that the degree of anisotropy in permeability depends not only upon particle shape and alignment, but also on the three-dimensional structure of the pack. In random packs, more oblate particles and higher degrees of particle alignment lead to reduced permeability perpendicular to the direction of particle alignment compared to the direction parallel to particle alignment.  相似文献   

Learning with Local Help: Expanding the Dialogue on Climate Change and Water Management in the Okanagan Region, British Columbia, Canada     

Stewart Cohen  Denise Neilsen  Scott Smith  Tina Neale  Bill Taylor  Mark Barton  Wendy Merritt  Younes Alila  Philippa Shepherd  Roger Mcneill  James Tansey  Jeff Carmichael  Stacy Langsdale 《Climatic change》2006,75(3):331-358

The research activity described in this report is a comprehensive regional assessment of the impacts of climate change on water resources and options for adaptation in the Okanagan Basin. The ultimate goal of the project is to develop integrated climate change and water resource scenarios to stimulate a multistakeholder discussion on the implications of climate change for water management in the region. The paper describes two main objectives: (a) providing a set of research products that will be of relevance to regional interests in the Okanagan, and (b) establishing a methodology for participatory integrated assessment of regional climate change impacts and adaptation that could be applied to climate-related concerns in Canada and other countries. This collaborative study has relied on field research, computer-based models, and dialogue exercises to generate an assessment of future implications, and to learn about regional views on the prospects for adaptation. Along the way, it has benefited from strong partnerships with governments, researchers, local water practitioners, and user groups. Building on the scenario-based study components, and a series of interviews and surveys undertaken for the water management and adaptation case study components, a set of stakeholder dialogue sessions were organized which focused on identifying preferred adaptation options and processes for their implementation. Rather than seeking consensus on the “best” option or process, regional interests were asked to consider a range of available options as part of an adaptation portfolio that could address both supply side and demand side aspects of water resources management in the Okanagan. The Canadian Crown reserves the right to retain a non-exclusive, royalty free licence in and to any copyright.  相似文献