Sedimentation cycles in a river-mouth tidal freshwater marsh     

Gregory B. Pasternack  Grace S. Brush 《Estuaries and Coasts》1998,21(3):407-415

Tidal freshwater marshes are critical buffers that exist at the interface between watersheds and estuaries. Little is known about the physical dynamics of tidal freshwater marsh evolution. Over a 21-mo period, July 1995 to March 1997, measurements were made of biweekly sediment deposition at 23 locations in a 3.8-ha tidal freshwater marsh in the Bush River subestuary of the upper Chesapeake Bay. Biweekly accumulation showed high spatial and temporal variability, ranging from ?0.28 g cm^?2 to 1.15 g cm^?2. Spatial variability is accounted for by habitat differences including plant associations, elevation, and hydrology. Temporal variability is accounted for by interannual climate variability, the growth cycles of marsh plants, stream-marsh interactions, forest-marsh interactions, and animal activity.  相似文献   

Paleozoic–early Mesozoic gold deposits of the Xinjiang Autonomous Region, northwestern China   总被引：12，自引：0，他引：12  

Zongyao Rui  Richard J. Goldfarb  Yumin Qiu  Taihe Zhou  Renyi Chen  Franco Pirajno  Grace Yun 《Mineralium Deposita》2002,37(3-4):393-418

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Mapping East African tropical forests and woodlands — A comparison of classifiers     

Grace Nangendo  Andrew K. Skidmore  Henk van Oosten 《ISPRS Journal of Photogrammetry and Remote Sensing》2007,61(6):393-404

In mapping the forest–woodland–savannah mosaic of Budongo Forest Reserve, Uganda, four classification methods were compared, i.e. Maximum Likelihood classifier (MLC), Spectral Angle Mapper (SAM), Maximum Likelihood combined with an Expert System (MaxExpert) and Spectral Angle Mapper combined with an Expert System (SAMExpert). The combination of conventional classifiers with an Expert System proved to be an effective approach for forest mapping. This was also the first time that the SAMExpert had been used in the mapping of tropical forests. SAMExpert not only maps with high accuracy, but is also fast and easy to use, making it attractive for use in less developed countries. Another advantage is that it can be executed on a standard PC set up for image processing.Combining the conventional classifiers (MLC and SAM) with the Expert System significantly improved the classification accuracy. The highest overall accuracy (94.6%) was obtained with SAMExpert. The MaxExpert approach yielded a map with an accuracy of 85.2%, which was also significantly higher than that obtained using the conventional MLC approach.The SAMExpert classifier accurately mapped individual classes. Of the four classes of woodland mapped, the Open Woodland (with Terminalia) and Wooded Grassland classes were more accurately mapped using SAMExpert. The Open Woodland had been previously identified by ecologists, but had never been mapped.  相似文献   

Polar 5—an electron accelerator experiment within an aurora. 1. Instrumentation and geophysical conditions     

B.N. Maehlum  K. Måseide  K. Aarsnes  A. Egeland  B. Grandal  J. Holtet  T.A. Jacobsen  N.C. Maynard  F. Søraas  J. Stadsnes  E.V. Thrane  J. Trøim 《Planetary and Space Science》1980,28(3):259-278

A “mother-daughter” rocket was launched from Andøya, Norway, February 1 1976 over two auroral structures. The “daughter” payload carried a 10keV electron accelerator and the “mother” carried a series of diagnostic instruments for monitoring optical and wave effects generated through beam-atmospheric interactions and production of secondary electrons.The experimental details are presented in this paper together with a survey of some of the results. This paper is also intended as a reference for a series of accompanying papers.  相似文献   

Spatio-temporal pattern of viral meningitis in Michigan, 1993-2001     

Sharon K. Greene  Mark A. Schmidt  Mary Grace Stobierski  Mark L. Wilson 《Journal of Geographical Systems》2005,7(1):85-99

To characterize Michigans high viral meningitis incidence rates, 8,803 cases from 1993–2001 were analyzed for standard epidemiological indices, geographic distribution, and spatio-temporal clusters. Blacks and infants were found to be high-risk groups. Annual seasonality and interannual variability in epidemic magnitude were apparent. Cases were concentrated in southern Michigan, and cumulative incidence was correlated with population density at the county level (r=0.45, p<0.001). Kulldorffs Scan test identified the occurrence of spatio-temporal clusters in Lower Michigan during July–October 1998 and 2001 (p=0.01). More extensive data on cases, laboratory isolates, sociodemographics, and environmental exposures should improve detection and enhance the effectiveness of a Space-Time Information System aimed at prevention.The authors gratefully acknowledge Dr. Duane Newton, former manager of the Virology Section, Michigan Department of Community Health Bureau of Laboratories, for his provision of data on viral isolates. We also appreciate the contributions of Drs. Leah Estberg and Dunrie Greiling for ClusterSeer support, Scott Swan for his assistance with ArcView GIS, and Dr. Edward L. Ionides for his advice on time series analysis. We are grateful to Dr. Pierre Goovaerts and two anonymous reviewers for their insightful comments on an earlier draft of this paper. This project was supported in part by a grant from the National Oceanic and Atmospheric Administrations Joint Program on Climate Variability and Human Health, a consortium including the EPA, NASA, NSF, and EPRI (NA16GP2361) to MLW.  相似文献   

Development of a Multimetric Index for Integrated Assessment of Salt Marsh Ecosystem Condition     

Jessica L. Nagel  Hilary A. Neckles  Glenn R. Guntenspergen  Erika N. Rocks  Donald R. SchoolmasterJr  James B. Grace  Dennis Skidds  Sara Stevens 《Estuaries and Coasts》2018,41(2):334-348

Tools for assessing and communicating salt marsh condition are essential to guide decisions aimed at maintaining or restoring ecosystem integrity and services. Multimetric indices (MMIs) are increasingly used to provide integrated assessments of ecosystem condition. We employed a theory-based approach that considers the multivariate relationship of metrics with human disturbance to construct a salt marsh MMI for five National Parks in the northeastern USA. We quantified the degree of human disturbance for each marsh using the first principal component score from a principal components analysis of physical, chemical, and land use stressors. We then applied a metric selection algorithm to different combinations of about 45 vegetation and nekton metrics (e.g., species abundance, species richness, and ecological and functional classifications) derived from multi-year monitoring data. While MMIs derived from nekton or vegetation metrics alone were strongly correlated with human disturbance (r values from ?0.80 to ?0.93), an MMI derived from both vegetation and nekton metrics yielded an exceptionally strong correlation with disturbance (r = ?0.96). Individual MMIs included from one to five metrics. The metric-assembly algorithm yielded parsimonious MMIs that exhibit the greatest possible correlations with disturbance in a way that is objective, efficient, and reproducible.  相似文献   

Slushflows: science and planning considerations for an expanding hazard     

Grace Relf  James M. Kendra  Robert M. Schwartz  Daniel J. Leathers  Delphis F. Levia 《Natural Hazards》2015,78(1):333-354

Slushflows are natural hazards that pose considerable danger to communities across the globe. These events are characterized by the rapid mass movement of water-inundated snow downslope, and they cause economic damage as well as fatalities in many different climates and regions. As the global climate changes and human populations and industries potentially expand to higher latitudes, it will be important to fully understand the slushflow hazard since an anticipated increase in the frequency of rain-on-snow events and an earlier spring thaw would likely increase the probability of slushflows. This article: (1) summarizes the factors that favor the development of slushflows; (2) discusses the hazard management implications of slushflows; (3) examines the policies employed to prevent and mitigate slushflow damage; and (4) sets out the need for modifications in hazard management systems. Conclusions drawn hope to address future research needs in an effort to create policies that better suit the needs of at-risk communities.  相似文献   

Engaging Communities for Success: social impact assessment and social licence to operate at Northparkes Mines,NSW     

Grace Michell 《The Australian geographer》2013,44(4):435-459

Social issues are critical to the mining industry. This study investigates how social issues have been, and are being, assessed and managed within this industry through a case study of Northparkes Mines in central west New South Wales (NSW). The research involved 29 interviews with mining executives, environmental consultants and citizens of Parkes, plus a document analysis of four environmental impact statements prepared between 1990 and 2012. Where appropriate, findings were extrapolated to the wider mining industry. The standard for social impact assessment in NSW and emerging industry guidelines on social responsibility were analysed against internationally accepted good practice. Interviews indicated greater potential to recognise the social impacts of mining in NSW and identified good practice impact assessment as only one component of a successful community engagement strategy. Complementary strategies are essential to extend the benefits of development to local communities and for companies to establish a ‘social licence to operate’. The successful approach taken by Northparkes Mines combined good practice impact assessment with a localised workforce, an integrated management team and context-specific community engagement practices. This study highlights that local communities can be empowered through development, that benefits can extend to both the community and the business and that the ongoing management of social issues will increasingly be critical to the success of the mining industry.  相似文献   

Gradients,Property Templates,and Land Use Change     

Daniel J. Bain  Grace S. Brush 《The Professional geographer》2013,65(2):224-237

The scarcity of historical individual-level data makes understanding historic land use decisions and the influence of physiochemical gradients on these decisions difficult. Here, we present several measures of early property agricultural quality based on commonly available data, including elevation and soil type. These analyses demonstrate the influence of physiochemical gradients on initial land division patterns in the Gywnns Falls watershed (Baltimore, Maryland). Moreover, we examine the influence of the template created by early property decisions on continuing human-driven landscape dynamics. This influence is illustrated by 1900-era forest cover patterns, park locations, and modern transportation networks.  相似文献   

Phenotypic plasticity of floral traits and pollination adaption in an alpine plant <Emphasis Type="Italic">Pedicularis siphonantha</Emphasis> D. Don when transplanted from higher to lower elevation in Eastern Himalaya     

Wen-Kui Dai  Grace Mercy Amboka  Edwin Luguba Kadiori  Qing-Feng Wang  Chun-Feng Yang 《山地科学学报》2017,14(10):1995-2002

Phenotypic plasticity and/or pollinator-mediated selection may be responsible for the changes in floral traits of plants when they are forced to live in new conditions. Although the two events could be independent, we hypothesized that phenotypic plasticity in floral traits might help to coordinate plant-pollinator interactions and enhance plant reproductive success in changing habitats. To test this hypothesis, we investigated floral traits and pollination on three natural populations of a lousewort (Pedicularis siphonantha) ranging at different elevations, as well as two downward transplanted populations in Shangeri-La County and Deqin County, northwest Yunnan, China. The results indicated that floral traits, i.e. phenology, longevity, display size, corolla tube length and pollen production differed significantly among populations. Moreover, or the two transplanted populations, floral traits diverged from their original populations, but converged to their host populations. Although the phenotypic plasticity in floral traits might be a rapid response to abiotic factor such as warmer environment, the changes in floral traits were found to be well adapted to pollination environment of the host population. Compared with plants of their original habitats in higher elevation, the transplanted individuals advanced flowering time, shortened flower longevity, reduced floral display size and pollen production, received higher visiting frequency and yielded more seeds. These findings suggested that phenotypic plasticity of floral traits might help plants adjust their resource allocation strategy between preand post-pollination stages in response to harsh or temperate conditions, which might correspondingly meet a pollinator-poor or hyphen rich environment. This would be beneficial for the widely-distributed species to adapt to various environmental changes.  相似文献