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21.
Scott Raulerson C. Rhett Jackson Nathan D. Melear Seth E. Younger Maura Dudley Katherine J. Elliott 《水文研究》2020,34(14):3045-3060
Dense understory thickets of the native evergreen shrub Rhododendron maximum expanded initially following elimination of American chestnut by the chestnut blight, and later in response to loss of the eastern hemlock due to hemlock woolly adelgid invasion. Rhododendron thickets often blanket streams and their riparian zones, creating cool, low-light microclimates. To determine the effect of such understory thickets on summer stream temperatures, we removed riparian rhododendron understory on 300 m reaches of two southern Appalachian Mountain headwater streams, while leaving two 300 m reference reaches undisturbed. Overhead canopy was left intact in all four streams, but all streams were selected to have a significant component of dead or dying eastern hemlock in the overstory, creating time-varying canopy gaps throughout the reach. We continuously monitored temperatures upstream, within and downstream of treatment and reference reaches. Temperatures were monitored in all four streams in the summer before treatments were imposed (2014), and for two summers following treatment (2015, 2016). Temperatures varied significantly across and within streams prior to treatment and across years for the reference streams. After rhododendron removal, increases in summer stream temperatures were observed at some locations within the treatment reaches, but these increases did not persist downstream and varied by watershed, sensor, and year. Significant increases in daily maxima in treatment reaches ranged from 0.9 to 2.6°C. Overhead canopy provided enough shade to prevent rhododendron removal from increasing summer temperatures to levels deleterious to native cold-water fauna (average summer temperatures remained below 16°C), and local temperature effects were not persistent. 相似文献
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AbstractNatural resource challenges often span administrative jurisdictions and include actors and processes operating at different spatial and political scales. We applied concepts of new environmental governance to analyze Oregon’s approach to greater sage-grouse conservation. Through one in-depth case study in Lake County, we traced features of new environmental governance (cross-scale interactions, decentralization, and capacities of actors) through different governance levels. Interviews and qualitative analysis revealed that decentralization of administrative functions facilitated cross-scale interactions and relied on intermediaries, gap-filling, and perceptions of legitimacy at lower levels. State and agency guidelines steered the effort and were accompanied by financial and technical resources from multiple arenas, which increased local capacity. This study adds to the understandings of environmental governance for implementing multi-actor, multi-level conservation arrangements in resource-dependent communities. Further exploration of connections between higher levels and local contexts will reveal important, new ways to link policies with on-the-ground outcomes. 相似文献
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Thomas D. Hamilton Gall M. Ashley Katherine M. Reed Charles E. Schweger 《Quaternary Research》1993,39(3)
Sediments exposed at Epiguruk, a large cutbank on the Kobuk River about 170 km inland from Kotzebue Sound, record multiple episodes of glacial-age alluviation followed by interstadial downcutting and formation of paleosols. Vertebrate remains from Epiguruk include mammoth, bison, caribou, an equid, a canid, arctic ground squirrel, lemmings, and voles. Radiocarbon ages of bone validated by concordant ages of peat and wood span the interval between about 37,000 and 14,000 yr B.P. The late Pleistocene pollen record is dominated by Cyperaceae, with Artemisia, Salix, Betula, and Gramineae also generally abundant. The fossil record from Epiguruk indicates that the Kobuk River valley supported tundra vegetation with abundant riparian willows during middle and late Wisconsin time. Large herbivores were present during the height of late Wisconsin glaciation as well as during its waning stage and the preceding interstadial interval. The Kobuk River valley would have been a favorable refugium for plants, animals, and possibly humans throughout the last glaciation. 相似文献
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Paul A. Morris 《Contributions to Mineralogy and Petrology》1986,93(2):207-214
Basanites and alkali basalts from Oberon, NSW, Australia contain variable abundances of small Cr-diopside lherzolite xenoliths. Despite a limited range in (metamorphic) textures and modal mineralogy, there is significant variation in mineral chemistry. Mineral thermometric data applied to the geotherm of O'Reilly and Griffin (1985) suggests equilibration over a narrow pressure interval corresponding to depths of 30–45 km. These data show that significant compositional variations exist over a small depth interval in the subcontinental mantle.Basaltic host rocks show near-primary chemical characteristics. Mildly and strongly incompatible element (i.e. D< 1 and D1 respectively) concentrations have been used to constrain the modal amounts of clinopyroxene and garnet in a presumed garnet peridotite mantle source. Estimated proportions of (ol+opx)=73%; cpx=16%; gar= 11% closely resemble source compositions for other basaltic rocks of eastern Australia. Batch partial melting of this source in the range F=9.5–15% applied to the available REE data suggests the source is enriched relative to chondrite 8–10 × La, 2.1–2.4 × Tb and 2.5–3.7 × Yb. 相似文献
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Double-packer injection tests have been carried out in a borehole in the Chalk of Hampshire and a borehole in the Permian Penrith Sandstone of Cumbria, England. The tests have been supplemented by borehole logging and television inspections and by laboratory measurements on cores. A new mathematical treatment has enabled results to be calculated for injection test intervals containing fissures. In both formations, transmissivity immediately around the borehole is dominated by a few major fissures. In the Penrith Sandstone there is good agreement between intergranular hydraulic conductivity measurements and packer-test results in the portions of the borehole which do not contain major fissures. In the Chalk, the packer-test values are always higher than the intergranular measurements, suggesting that some degree of fissuring is present throughout. 相似文献
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