Paleolimnology of Lake Winnipeg     

Brian J. Todd  C. F. Michael Lewis  L. Harvey Thorleifson  Erik Nielsen  William M. Last 《Journal of Paleolimnology》1998,19(3):211-213

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Organic carbon and cation associations in humic material from pond water and sediment     

James J. Alberts  Todd J. Dickson 《Organic Geochemistry》1985,8(1):55-64

Organic matter was isolated from the water columns and sediments of two pond systems in the south-eastern United States. Water column material was ultrafiltered to provide three fractions, i.e. <0.45 μm, but > 50,000 daltons; <50,000 daltons, but > 5000 daltons; and <5000 daltons. Sedimentary organic matter was separated into humic acid and fulvic acid fractions based on solubility criteria and the humic acid fraction was ultrafiltered to provide the same fractions as the water column isolates. All fractions were analysed for organic carbon, Al, Ca, Cu, Fe, Mg and Mn. Infra-red spectra were also measured for the sedimentary organic fractions. Organic matter isolated from the water column of the two ponds had similar organic carbon and elemental distributions, as did the organic matter isolated from the two sediments. However, significant differences in the organic carbon and elemental distributions were observed for water column and sedimentary organic matter isolated from the same pond. These studies have relevance to diagenetic alterations of organic matter and geochemical cycles of elements within lakes.  相似文献   

Opinion I     

Todd Giddings 《Ground Water Monitoring & Remediation》1987,7(2):96-97

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Characteristics of summertime daily rainfall variability over South America and the South Atlantic Convergence Zone     

M. C. Todd  R. Washington  T. James 《Meteorology and Atmospheric Physics》2003,83(1-2):89-108

Summary ?This paper presents an objective analysis of the structure of daily rainfall variability over the South American/South Atlantic region (15°–60° W and 0°–40° S) during individual austral summer months of November to March. From EOF analysis of satellite derived daily rainfall we find that the leading mode of variability is represented by a highly coherent meridional dipole structure, organised into 2 extensive bands, oriented northwest to southeast across the continent and Atlantic Ocean. We argue that this dipole structure represents variability in the meridional position of the South Atlantic Convergence Zone (SACZ). During early and later summer, in the positive (negative) phase of the dipole, enhanced (suppressed) rainfall over eastern tropical Brazil links with that over the subtropical and extra-tropical Atlantic and is associated with suppressed (enhanced) rainfall over the sub-tropical plains and adjacent Atlantic Ocean. This structure is indicative of interaction between the tropical, subtropical and temperate zones. Composite fields from NCEP reanalysis products (associated with the major positive and negative events) show that in early and late summer the position of the SACZ is associated with variability in: (a) the midlatitude wave structure, (b) the position of the continental low, and (c) the zonal position of the South Atlantic Subtropical High. Harmonic analysis of the 200 hPa geopotential anomaly structure in the midlatitudes indicates that reversals in the rainfall dipole structure are associated primarily with variability in zonal wave 4. There is evidence of a wave train extending throughout the midlatitudes from the western Pacific into the SACZ region. During positive (negative) events the largest anomalous moisture advection occurs within westerlies (easterlies) primarily from Amazonia (the South Atlantic). In both phases a convergent poleward flow results along the leading edge of the low-level trough extending from the tropics into temperate latitudes. High summer events differ from those in early and late summer in that the rainfall dipole is primarily associated with variability in the phase of zonal wave 3, and that tropical-temperate link is not clearly evident in positive events. Received May 31, 2001; revised October 17, 2001; accepted June 13, 2002  相似文献   

Designing Monitoring Programs to Effectively Evaluate the Performance of Natural Attenuation     

Todd H. Wiedemeier  Patrick E. Haas 《Ground Water Monitoring & Remediation》2002,22(3):124-135

Natural attenuation processes affect the fate and transport of organic compounds in many hydrologic systems. Over the last several years, regulatory agencies and environmental professionals have come to recognize the importance of these natural processes in effecting contaminant attenuation. When they are shown to be protective of human health and the environment, and when a well-designed monitoring program is in place to document the efficiency of these processes, they can be a valuable component of site remediation strategies.  相似文献   

吐哈盆地煤成烃研究新进展   总被引：7，自引：0，他引：7  

程克明  熊英  J M Moldowan  J Greene Todd 《沉积学报》2002,20(3):456-461

运用生物标记物及碳同位素等地化参数对吐鲁番 -哈密盆地的原油及其源岩进行了油源对比 |结果将该区原油分为三类 :第一类原油 |根据生标特征分析其具有显著的淡水环境、藻含量低、细菌影响大、C₂₉甾烷含量高、C₃₀4_α- 甲基甾烷低、C₂₄ 四环烷和C₁₉三环烷含量高和碳同位素偏重 (δ13C为 - 25‰~ - 27‰ )的特点 |初步对比结果 |本区西山窑组的煤是该类原油的主要源岩;第二类原油 |富含藻类物质(C₂₇甾烷与C₃₀4_α-甲基甾烷含量较高 ) |该类原油可能来自侏罗系的富藻湖相泥岩;第三类原油 |全油碳同位素δ13C为 - 30‰~ - 32‰ |这类原油的生标反映出其源岩相的特征为缺氧、咸水、中等含藻的湖相沉积 (高含量的伽玛蜡烷和 β_-胡萝卜烷|C₃₅/C₃₄藿烷比值大等 )。  相似文献   

The Working World of the Paladar: The Production of Contradictory Space during Cuba's Period of Fragmentation*     

Edward &#x;&#x;&#x;&#x;&#x;&#x;L. Jackiewicz  Todd Bolster 《The Professional geographer》2003,55(3):372-382

This article examines the social spaces of self‐employment in Havana, Cuba, to uncover the deeply conflicting and contradictory values that comprise the dialectics of state–society relations. These spaces and the many actors who traverse them provide important insight into the complexity surrounding contemporary Cuba. Through detailed research into one form of self‐employment, paladares (small in‐home restaurants), this article examines how paladares have come to reflect the struggle for society and state to mediate the multitude of external and internal pressures amongst the current geopolitical climate. Using interviews conducted during several visits in 1999 and 2000, we demonstrate that paladares do not necessarily represent a capitalist transition. Rather, they embody the struggle to mediate contradictory spaces through the assertion of the self in the discourse of change.  相似文献   

A GIS‐based variable source area hydrology model     

Jane R. Frankenberger  Erin S. Brooks  M. Todd Walter  Michael F. Walter  Tammo S. Steenhuis 《水文研究》1999,13(6):805-822

Effective control of nonpoint source pollution from contaminants transported by runoff requires information about the source areas of surface runoff. Variable source hydrology is widely recognized by hydrologists, yet few methods exist for identifying the saturated areas that generate most runoff in humid regions. The Soil Moisture Routing model is a daily water balance model that simulates the hydrology for watersheds with shallow sloping soils. The model combines elevation, soil, and land use data within the geographic information system GRASS, and predicts the spatial distribution of soil moisture, evapotranspiration, saturation‐excess overland flow (i.e., surface runoff), and interflow throughout a watershed. The model was applied to a 170 hectare watershed in the Catskills region of New York State and observed stream flow hydrographs and soil moisture measurements were compared to model predictions. Stream flow prediction during non‐winter periods generally agreed with measured flow resulting in an average r² of 0·73, a standard error of 0·01 m³/s, and an average Nash‐Sutcliffe efficiency R² of 0·62. Soil moisture predictions showed trends similar to observations with errors on the order of the standard error of measurements. The model results were most accurate for non‐winter conditions. The model is currently used for making management decisions for reducing non‐point source pollution from manure spread fields in the Catskill watersheds which supply New York City's drinking water. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Reappraisal of the ‘Cullenstown Formation’: Implications for the Lower Palaeozoic tectonic history of SE Ireland     

M. C. Bennett  W. M. Dunne  S. P. Todd 《Geological Journal》1989,24(4):317-329

The structurally attenuated greenschist facies metasedimentary succession at Cullenstown Strand in south Co. Wexford comprises three formations which in stratigraphic order are (1) the Quartzite Formation, (2) the Greywacke/Quartzite Formation, and (3) the Greywacke Formation. The entire sequence is inverted and lies within the lower limb of a large scale overturned D1 anticlinal structure that closes towards the southeast. The three formations are lithologically and sedimentologically similar to the Shelmaliere Quartzite, the Cullentra Greywacke, and Newtown Greywacke Formations of the Bray Group in the Forth Mountain - Ferrycarrig area that probably lie on the normal limb of the D1 structure. The Cullenstown strata are therefore considered to be part of the Bray Group in southeast Leinster, and hence Cambrian in age. The rocks were affected by three major phases of deformation. D1 produced an overturned anticline containing an important tectonic slide. The D1 structures are modified by upright D2 and D3 structures, but from regional considerations it is argued that D1 is restricted to strata of Cambrian to Lower Ordovician age in southeast Leinster. A model for the tectonic evolution of the southeastern part of the Leinster Basin during Cambro-Ordovician times is presented and discussed. In this model, the southeast margin of the Leinster Basin was delineated by a mylonite zone along the northwest margin of the Precambrian Rosslare Complex. Bray and Ribband Group sediments close to the margin were deformed during the Llanvirn as a consequence of basin inversion which caused shortening and thrusting of the basin fill across the Rosslare block. The D1 compressional structures were subsequently modified during a period of extension, marked by the resumption of sedimentation and outbreak of voluminous volcanicity near the basin margin during the Llandeilo and Caradoc. The D2 and D3 structures in the Bray and Ribband Groups are an expression of later Caledonian deformation.  相似文献   

The Application of GIS in Education Administration: Protecting Students from Hazardous Roads     

Fatemah Admadi Nejad Masouleh  Yuji Murayama  Todd Wendell Rho'Dess 《Transactions in GIS》2009,13(1):105-123

Though enrolment by proximity is an official educational policy in Iran, the lack of clearly defined school attendance areas has resulted in an informal open enrolment system where parents may choose public schools outside their residential areas. Two major consequences of parental choice are longer commutes to schools and increased use of motor vehicle transport. To delineate school attendance areas for public female junior high schools in the city of Rasht in Northern Iran, this research used the multiplicatively weighted Voronoi diagram (MWVD) technique to construct school attendance areas. The approach was shown to be useful in developing countries like Iran where accident fatalities are not only disproportionately high but the public school system lacks sufficient educational diversity to offset the societal costs of opting out of neighbourhood schools. A GIS-based specialist package was used for constructing the proposed school attendance areas. Given the MWVD utility in demarcating spaces so that all journeys within them are closest to a chosen point, the research concluded that proposed school attendance areas can result in shorter and more convenient commutes on foot for students. This can eliminate the need to travel by vehicle for the overwhelming majority of students and thus make their journeys more convenient and safer.  相似文献