An algorithm to aid varve counting and measurement from thin-sections     

Pierre Francus  Frank Keimig  Mark Besonen 《Journal of Paleolimnology》2002,28(2):283-286

An algorithm has been implemented to count and measure laminations from digital images of petrographic thin-sections. Boundaries and limits of laminations are first marked manually using imaging software. These marks are then exported to a workable format output file. Using the output file, the algorithm extracts the relevant information for lamination counts and thickness measurements along one or more parallel vertical lines. Compared to manual counts, the use of the algorithm improves the accuracy of measurements and speeds up the process. The method requires tools commonly available in most laboratories, i.e., a digital camera or a flat bed scanner with transparency capability and a desktop computer with 64 MB of RAM. From the algorithm, two utilities are implemented in Visual Basic for Applications and Fortran to be used on both Apple Macintosh and a PC-compatible, with Adobe^® Photoshop^®.  相似文献   

Derivation of a microstructural poroelastic model   总被引：7，自引：0，他引：7  

Mark Chapman  Sergei V. Zatsepin  Stuart Crampin 《Geophysical Journal International》2002,151(2):427-451

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Mountain Rivers: Ellen E. Wohl, American Geophysical Union, Washington, DC 2000, v+320 pp., US$39.00, softcover, ISBN 0-87590-318-5     

Mark Fonstad 《Geomorphology》2002,46(3-4)

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Remote sensing documentation of historic rangeland remediation treatments in southern New Mexico     

Albert Rango  Sarah Goslee  Jeff Herrick  Mark Chopping  Kris Havstad  Laura Huenneke  Robert Gibbens  Reldon Beck  Robert McNeely 《Journal of Arid Environments》2002,50(4):549

The Jornada Experimental Range and the New Mexico State University Chihuahuan Desert Rangeland Research Center are fruitful areas to study the long-term effects of rangeland remediation treatments which started in the 1930s. A number of diverse manipulations were completed under the direction of federal agency and university scientists, and abundant remote sensing imagery is available to assist in relocating the treatments and evaluating their success. This is particularly important because few of the treatments were maintained following the loss of scientific personnel coinciding with the start of World War II, and most records of Civilian Conservation Corps scientific work were lost with the disbanding of the agency in 1942. Aerial photography, which was systematically used to image the United States beginning in the 1930s, can be used to identify types of treatments, measure areal coverage, estimate longevity, and help plan locations for new experiments. No long-lasting vegetation response could be determined for contour terraces, brush water spreaders, strips grubbed free of shrubs (despite the fact that these strips have remained visible for 65 years), and mechanical rootplowing and seeding. Distinct positive, long-term vegetation responses could be seen in aerial photos for water retention dikes, certain fenced exclosures, and some boundaries where different land management practices meet. It appears from both aerial photos and existing conventional records that experimental manipulation of rangelands has often been ineffective on the landscape scale because treatments are not performed over large enough contiguous areas and hydrological and ecological processes overwhelm the treatments. In addition, treatments are not maintained over time, treatment evaluation periods are sometimes too short, multi-purpose treatments are not used to maximize effects, and treatments are often not located in appropriate sites.  相似文献   

Iron oxide formation in the active oxidation front above sapropel S1 in the eastern Mediterranean Sea as derived from low-temperature magnetism   总被引：1，自引：0，他引：1  

Hilde F. Passier  Mark J. Dekkers 《Geophysical Journal International》2002,150(1):230-240

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Spatial distribution and geomorphology of lunette dunes on the High Plains of Western Kansas: implications for geoarchaeological and paleoenvironmental research     

Mark W. Bowen  William C. Johnson  Dylan A. King 《自然地理学》2018,39(1):21-37

The High Plains are a vast, low relief landscape that contains thousands of upland-embedded depressional playa wetlands. Lunettes are isolated dunes that form from prolonged periods of aeolian deposition along the downwind margin of some larger playas. Playa-lunette systems are important landscape elements that have the potential to preserve high-resolution records of past environments, and several archeological sites have been associated with playa-lunette systems throughout the High Plains. While a comprehensive playa wetland geospatial database has been developed for the High Plains, lunettes have only been mapped for the Southern High Plains of Texas and New Mexico. The purpose of this research was to map and characterize the geomorphology of all lunettes associated with playas in the High Plains and bordering regions of western Kansas. Results indicate 129 lunettes are associated with 104 playas in Kansas. All lunettes are associated with playas larger than 5 ha, and about 10% of these larger playas have a lunette. Lunette height ranges from approximately 1.5–12 m, with a median height of 3 m. Most lunettes (60%) are in Finney, Gray, Lane, and Scott counties, which have broad, flat uplands with few major drainages upwind of playas and lunettes.  相似文献   

From Shiny Shoes to Muddy Reality: Understanding How Meso-State Actors Negotiate the Implementation Gap in Participatory Forest Management     

Anne Kairu  Caroline Upton  Mark Huxham  Kiplagat Kotut  Robert Mbeche  James Kairo 《社会与自然资源》2018,31(1):74-88

Recent research on participatory forest management (PFM) in the global south has highlighted the existence of a widespread “implementation gap” between the ambitious intent enshrined in legislation and the often partial, disappointing rollout of devolved forest governance on the ground. Here, through an ethnographic case study of forest officers (FOs) in Kenya, we draw on a framework of critical institutionalism to examine how key meso-level actors, or “interface bureaucrats,” negotiate and challenge this implementation gap in everyday forest governance. We go beyond consideration of institutional bricolage in isolation or as an aggregate category, to analyze how bricolage as aggregation, alteration, and/or articulation is variously driven, shaped, and constrained by FOs’ multiple accountabilities and agency. Our analysis highlights the locally specific, contingent, and mutually reinforcing nature of accountability, agency and bricolage, and their explanatory power in relation to the performance and nature of “actually existing” PFM.  相似文献   

Paleolimnology of a freshwater estuary to inform Area of Concern nutrient delisting efforts     

Elizabeth E. Alexson  Euan D. Reavie  Richard P. Axler  Sergiy V. Yemets  Pavel A. Krasutsky  Mark B. Edlund  Robert W. Pillsbury  Diane Desotelle 《Journal of Paleolimnology》2018,59(3):373-395

The St. Louis River Estuary (SLRE), a freshwater estuary bordering Duluth, Minnesota, Superior, Wisconsin, and the most western point of Lake Superior (46.74°, ? 92.13°), has a long history of human development since Euro-American settlement ~ 200 years ago. Due to degradation from logging, hydrologic modification, industrial practices, and untreated sewage, the SLRE was designated an Area of Concern in 1987. Action has been taken to restore water quality including the installation of the Western Lake Superior Sanitary District in 1978 to help remove beneficial use impairments. A better understanding of historical impacts and remediation is necessary to help document progress and knowledge gaps related to water quality, so a paleolimnological study of the SLRE was initiated. Various paleolimnological indicators (pigments, diatom communities, and diatom-inferred phosphorus) were analyzed from six cores taken throughout the SLRE and another from western Lake Superior. Reductions in eutrophic diatom taxa such as Cyclotella meneghiniana and Stephanodiscus after 1970 in certain cores suggest an improvement in water quality over the last 40 years. However, in cores taken from estuarine bay environments, persistence of eutrophic taxa such as Cyclostephanos dubius and Stephanodiscus binderanus indicate ongoing nutrient problems. Sedimentary pigments also indicate cyanobacteria increases in bays over the last two decades. Diatom model-inferred phosphorus and contemporary monitoring data suggest some of the problems associated with excess nutrient loads have been remediated, but modern conditions (internal phosphorus loading, changing climate) may be contributing to ongoing water quality impairments in some locations. The integrated record of biological, chemical, and physical indicators preserved in the sediments will aid state and federal agencies in determining where to target their resources.  相似文献   

MAGNETOSTRATIGRAPHY AND ITS IMPLICATIONS OF CORE DY03 IN THE YANGTZE RIVER DELTA     

Mark Dekker  HUANG Xiang-tong  ZHENG Hong-bo  YANG Shou-ye  Mark Dekker  XIE Xin  ZHANG Zhen-quan  FANG Guo-qing 《海洋地质与第四纪地质》2008,28(6)

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Long-term morphodynamic evolution of estuaries: An inverse problem     

Harshinie Karunarathna  Dominic Reeve  Mark Spivack 《Estuarine, Coastal and Shelf Science》2008

A new technique for predicting long-term variations in estuary morphology is developed using a morphological evolution equation that isolates diffusive and non-diffusive processes in estuaries. The contribution from non-diffusive processes to the morphological changes of the estuary is incorporated in the governing equation by a source function. The source function is derived by solving an inverse problem using historic survey data of the Humber estuary, UK covering a period of 150 years.  相似文献