Records of aquatic pollen and sediment properties as indicators of late-Quaternary Alaskan lake levels     

Mary E. Edwards  Nancy H. Bigelow  Bruce P. Finney  Wendy R. Eisner 《Journal of Paleolimnology》2000,24(1):55-68

We investigated whether techniques developed to evaluate qualitative lake-level changes in the temperate zone can be used in sub-arctic and arctic Alaska. We focused on aquatic pollen records and sediment properties (loss-on-ignition and magnetic susceptibility) from centrally-located sediment-surface samples and cores, as these are the most commonly reported data in the literature. Modern aquatic pollen values are generally low (< 5%) and may be zero, even in lakes with abundant aquatic macrophytes. Greater diversity and higher values of aquatic pollen are likely at depths < 5 m, but pollen is found in depths up to 15 m. It is absent at depths > 20 m. Spores of Isoetes and Equisetum and Pediastrum cell-nets, when present, tend to be widely distributed, even in deep water. At Birch Lake, interior Alaska, trends in aquatic taxa and sediment characteristics for the last ca. 12,000 ¹⁴C yrs recorded in a single, deep-water core reflect the same water-level changes as do transect-based lake-level reconstructions - if modern distributional characteristics of pollen and spores are taken into account. The lake rose from extremely low levels at ca. 12,000 ¹⁴C yr B.P. After a period of fluctuation, it rose to a relatively high level by ca. 8000 ¹⁴C yr B.P. and then stabilized. A preliminary survey of aquatic pollen trends from other lake-sediment records suggests that the period ca. 11,000-8000 ¹⁴C yr B.P. may have seen relatively low lake levels in north-western and interior Alaska and high levels thereafter. Changes in aquatic pollen and sediments are evident in north-eastern interior lakes at the same time, but they are more difficult to interpret. Aquatic pollen productivity in Alaskan lakes may partly depend on factors other than water depth (e.g. temperature, pH, nutrient status, or length of the ice-free season). An Alaska-wide reconstruction of late-Quaternary lake levels based on extant single-core data would be best done after further study of contributing factors that may control sediment properties and aquatic pollen distribution.  相似文献   

FOREWORD     

Mary R. Albert  Susan Taylor 《水文研究》1996,10(12):1551-1551

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UV-B induced immunomodulation: a health risk     

Johan Garssen  Mary Norval  Henk Van Loveren 《Polar research》1999,18(2):339-343

The depletion in stratospheric ozone and changes in life-styles are likely to lead to an increased exposure to sunlight, including the UV-B waveband. Such irradiation may induce immunomodulation and therefore have adverse effects on human health. Alterations in immune responses could affect not only photocarcinogenesis but also resistance to infections, certain allergies and autoimmunity, and vaccination efficacy. In the present study, the risk of increased UV-B exposure has been estimated with respect to the resistance to a bacterial ( Listeria monocytogenes ) and a viral (herpes simplex virus) infection. The data indicate that suberythemal UV-B irradiation can have significant effects on immune responses to certain infectious diseases in human subjects.  相似文献   

Bioremediation in Fractured Rock: 1. Modeling to Inform Design,Monitoring, and Expectations          下载免费PDF全文

Claire R. Tiedeman  Allen M. Shapiro  Paul A. Hsieh  Thomas E. Imbrigiotta  Daniel J. Goode  Pierre J. Lacombe  Mary F. DeFlaun  Scott R. Drew  Carole D. Johnson  John H. Williams  Gary P. Curtis 《Ground water》2018,56(2):300-316

Field characterization of a trichloroethene (TCE) source area in fractured mudstones produced a detailed understanding of the geology, contaminant distribution in fractures and the rock matrix, and hydraulic and transport properties. Groundwater flow and chemical transport modeling that synthesized the field characterization information proved critical for designing bioremediation of the source area. The planned bioremediation involved injecting emulsified vegetable oil and bacteria to enhance the naturally occurring biodegradation of TCE. The flow and transport modeling showed that injection will spread amendments widely over a zone of lower‐permeability fractures, with long residence times expected because of small velocities after injection and sorption of emulsified vegetable oil onto solids. Amendments transported out of this zone will be diluted by groundwater flux from other areas, limiting bioremediation effectiveness downgradient. At nearby pumping wells, further dilution is expected to make bioremediation effects undetectable in the pumped water. The results emphasize that in fracture‐dominated flow regimes, the extent of injected amendments cannot be conceptualized using simple homogeneous models of groundwater flow commonly adopted to design injections in unconsolidated porous media (e.g., radial diverging or dipole flow regimes). Instead, it is important to synthesize site characterization information using a groundwater flow model that includes discrete features representing high‐ and low‐permeability fractures. This type of model accounts for the highly heterogeneous hydraulic conductivity and groundwater fluxes in fractured‐rock aquifers, and facilitates designing injection strategies that target specific volumes of the aquifer and maximize the distribution of amendments over these volumes.  相似文献   

Bioremediation in Fractured Rock: 2. Mobilization of Chloroethene Compounds from the Rock Matrix          下载免费PDF全文

Allen M. Shapiro  Claire R. Tiedeman  Thomas E. Imbrigiotta  Daniel J. Goode  Paul A. Hsieh  Pierre J. Lacombe  Mary F. DeFlaun  Scott R. Drew  Gary P. Curtis 《Ground water》2018,56(2):317-336

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Properties of dust source material and volcanic ash in Iceland     

Mary K. Butwin  Melissa A. Pfeffer  Sibylle von Löwis  Eivind W. N. Støren  Eniko Bali  Throstur Thorsteinsson 《Sedimentology》2020,67(6):3067-3087

The volcanic origin, primarily basaltic, of most of the surface material in Iceland influences its physical properties and appearance. Size distributions, shape analyses and melting experiments were made for surface material collected in high-erosion dust source areas and fresh volcanic ash deposits to determine whether they differ from one another and from dust from other major dust sources. The major differences found between Icelandic dust and dust from other major dust sources in the world, such as the Sahara, are in the particle shapes, lower density and darker colour. Icelandic dust particles greater than 20 μm retain volcanic morphological properties that are also found in fresh volcanic ash. Dust and fresh volcanic ash particles less than 20 μm are crystalline and blocky in nature, similar to the dust from other global source regions. The finer grained (<20 μm) Icelandic particles will have similar suspension and transport behaviours and be similarly hazardous to health and infrastructure as non-Icelandic dust. The coarser particles (>20 μm) will have different suspension and transport behaviours than other dusts due to the volcanic morphology. Icelandic surface material has between 5% and 30% glassy particles compared to fresh volcanic ash which has more than 50% glassy particles. Glassy particles were observed to melt at a lower temperature than the mineral grains; and, as a result, volcanic ash is found to be more threatening to aircraft engines than the typical dust from Iceland. Icelandic dust was observed to be blocky, or plate-like in the respirable size fraction, suggesting similar health hazards as dust from other regions.  相似文献   

Differentiation of clay resources on a limestone plain: The analysis of clay utilization during the Maya Formative at K'axob Belize     

Mary Lee Bartlett  Hector Neff  Patricia A. McAnany 《Geoarchaeology》2000,15(2):95-133

Differentiating clay resources in a uniform limestone plain, such as occurs in northern Belize, offers special challenges for the archaeologist. Combining data from soil mapping with petrographic and neutron activation analysis provides a mechanism for distinguishing possible resource areas. This study employed each of these differing avenues of analysis to determine possible clay resource areas used during the Maya Formative in northern Belize Central America. The results indicate that clay usage changed significantly from the Middle Formative period to the end of Late Formative period. These changes suggest a move to increased localized production and resource exploitation by the end of the period. © 2000 John Wiley & Sons, Inc.  相似文献   

Cave bears and paleolithic artifacts in Yarimburgaz Cave,Turkey: Dissecting a palimpsest     

Mary C. Stiner  Güven Arsebük  F. Clark Howell 《Geoarchaeology》1996,11(4):279-327

This article addresses the taphonomic issues surrounding artifact-bear associations in Yarimburgaz Cave, northwestern Turkey. Our purpose is to evaluate the circumstances of bone assemblage formation in the Middle Pleistocene deposits of the cave, identifying the agencies responsible for the accumulations and the causes of bone damage before and following deposition. Pleistocene species representation, bone damage, body part representation, and mortality data indicate that cave bear remains in Yarimburgaz are unrelated to hominid use of the same site. None of the observations on the cave bear remains contradicts the expectations developed from modern wildlife accounts of modern bear behavior; these accumulations resulted from mortality normally associated with hibernation over many generations of den use. Nonursid carnivores also played roles in bone collection and/or modification. We conclude that at least three distinct biological processes contributed to the formation of the Middle Pleistocene faunas: hibernating bears, bone-collecting carnivores such as wolves, and hominids in descending order of importance. The Yarimburgaz faunas represent palimpsests or overlays of many short-term depositional events, the close spatial associations of which are explained by slow or uneven sedimentation rates inside the cave. Although occupations by hominids appear to have been ephemeral in nature, hominids ultimately discarded nearly 1700 stone artifacts in Yarimburgaz Cave. The hominids did not discard many ungulate bones in the same circumstances. These observations suggest that hominid foraging efforts focused on resources other than large game while at the cave. © 1996 John Wiley & Sons, Inc.  相似文献