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71.
Rosemary W. H. Carroll Wendy Brown Wenming Dong Markus Bill Kenneth H. Willlams 《水文研究》2018,32(14):2187-2202
Critical zone influences on hydrologic partitioning, subsurface flow paths and reactions along these flow paths dictate the timing and magnitude of groundwater and solute flux to streams. To isolate first‐order controls on seasonal streamflow generation within highly heterogeneous, snow‐dominated basins of the Colorado River, we employ a multivariate statistical approach of end‐member mixing analysis using a suite of daily chemical and isotopic observations. Mixing models are developed across 11 nested basins (0.4 to 85 km2) spanning a gradient of climatological, physical, and geological characteristics. Hydrograph separation using rain, snow, and groundwater as end‐members indicates that seasonal contributions of groundwater to streams is significant. Mean annual groundwater flux ranges from 12% to 33% whereas maximum groundwater contributions of 17% to 50% occur during baseflow. The direct relationship between snow water equivalent and groundwater flux to streams is scale dependent with a trend toward self‐similarity when basins exceed 5.5 km2. We find groundwater recharge increases in basins of high relief and within the upper subalpine where maximum snow accumulation is coincident with reduced conifer cover and lower canopy densities. The mixing model developed for the furthest downstream site did not transfer to upstream basins. The resulting error in predicted stream concentrations points toward weathering reactions as a function of source rock and seasonal shifts in flow path. Additionally, the potential for microbial sulfate reduction in floodplain sediments along a low‐gradient, meandering portion of the river is sufficient to modify hillslope contributions and alter mixing ratios in the analysis. Soil flushing in response to snowmelt is not included as an end‐member but is identified as an important mechanism for release of solutes from these mountainous watersheds. End‐member mixing analysis used in combination with high‐frequency observations reveals important aspects of catchment hydrodynamics across scale. 相似文献
72.
Angela L. Doherty Robert J. Bodnar Benedetto De Vivo Wendy A. Bohrson Harvey E. Belkin Antonia Messina Robert J. Tracy 《Central European Journal of Geosciences》2012,4(2):338-355
The Aeolian Islands are an arcuate chain of submarine seamounts and volcanic islands, lying just north of Sicily in southern Italy. The second largest of the islands, Salina, exhibits a wide range of compositional variation in its erupted products, from basaltic lavas to rhyolitic pumice. The Monte dei Porri eruptions occurred between 60 ka and 30 ka, following a period of approximately 60,000 years of repose. The bulk rock composition of the Monte dei Porri products range from basaltic-andesite scoria to andesitic pumice in the Grey Porri Tuff (GPT), with the Monte dei Porri lavas having basaltic-andesite compositions. The typical mineral assemblage of the GPT is calcic plagioclase, clinopyroxene (augite), olivine (Fo72?84) and orthopyroxene (enstatite) ± amphibole and Ti-Fe oxides. The lava units show a similar mineral assemblage, but contain lower Fo olivines (Fo57?78). The lava units also contain numerous glomerocrysts, including an unusual variety that contains quartz, K-feldspar and mica. Melt inclusions (MI) are ubiquitous in all mineral phases from all units of the Monte dei Porri eruptions; however, only data from olivine-hosted MI in the GPT are reported here. Compositions of MI in the GPT are typically basaltic (average SiO2 of 49.8 wt %) in the pumices and basaltic-andesite (average SiO2 of 55.6 wt %) in the scoriae and show a bimodal distribution in most compositional discrimination plots. The compositions of most of the MI in the scoriae overlap with bulk rock compositions of the lavas. Petrological and geochemical evidence suggest that mixing of one or more magmas and/or crustal assimilation played a role in the evolution of the Monte dei Porri magmatic system, especially the GPT. Analyses of the more evolved mineral phases are required to better constrain the evolution of the magma. 相似文献
73.
Anthropogenic midden deposits are remarkably well preserved at the Neolithic settlement of Çatalhöyük and provide significant archaeological information on the types and nature of activities occurring at the site. To decipher their complex stratigraphy and to investigate formation processes, a combination of geoarchaeological techniques was used. Deposits were investigated from the early ceramic to late Neolithic levels, targeting continuous sequences to examine high resolution and broader scale changes in deposition. Thin‐section micromorphology combined with targeted phytolith and geochemical analyses indicates they are composed of a diverse range of ashes and other charred and siliceous plant materials, with inputs of decayed plants and organic matter, fecal waste, and sedimentary aggregates, each with diverse depositional pathways. Activities identified include in situ burning, with a range of different fuel types that may be associated with different activities. The complexity and heterogeneity of the midden deposits, and thus the necessity of employing an integrated microstratigraphic approach is demonstrated, as a prerequisite for cultural and palaeoenvironmental reconstructions. 相似文献
74.
David Morrill Anderson Bruce A. Bauer Charles R. Buckner Edward Gille Wendy S. Gross Michael Hartman Carrie Morrill Anju M. Shah Eugene R. Wahl 《Earth Science Informatics》2011,4(4):161-167
Reducing uncertainty in global temperature reconstructions of the past millennium remains the key issue in applying this record
to society’s pressing climate change problem. Reconstructions are collaborative, built on the research of hundreds of scientists
who apply their diverse scientific expertise and field and laboratory skill to create the individual proxy reconstructions
that underlie the multi-proxy, global average temperature time series. Web 2.0 features have enabled collaborative efforts
that improve the characterization of uncertainty. Raw data shared via a repository (the World Data Center for Paleoclimatology)
enable new reconstructions from the collection of user-generated data. Standards propagated by expert communities facilitate
quality control and interoperability. Open access to data and computer code promote transparency and make the science accessible
to a broader audience. Blogs, wikis, and listservs share background information and highlight contentious as well as unique
aspects of paleo science. A novel approach now underway, titled the Paleoclimate Reconstruction Challenge, and based on the
sharing of simulated data (pseudo-proxies) and reconstruction results, seeks to facilitate method development, further reducing
uncertainty. Broadly-useful aspects of the Challenge may find application in other fields. 相似文献
75.
76.
David Emerson Wendy Bellows Jason K. Keller Craig L. Moyer Ariana Sutton-Grier J. Patrick Megonigal 《Estuaries and Coasts》2013,36(3):471-481
The interaction of plant and microbial communities are known to influence the dynamics of methane emission in wetlands. Plant manipulations were conducted in an organic rich (JB-organic) and a mineral rich (JB-mineral) site in a tidal freshwater wetland to determine if plant removal impacted archaeal populations. In concert, a suite of process-based measurements also determined the effects of plant removal on rates of methanogenesis and Fe-reduction. The microbial populations were analyzed with clone libraries of the SSU ribosomal RNA (rRNA) gene from selected plots, and terminal restriction length polymorphism (tRFLP) of the SSU rRNA and the methyl-coenzyme M reductase (mcrA) gene. Overall, methanogenesis dominated anaerobic carbon mineralization at both sites during the most active growing season. A total of 114 SSU rRNA clones from four different plots revealed a diversity of Euryarchaeota including representatives of the Methanomicrobiales, Methanosarcinales and Thermoplasmatales. The clone libraries were dominated by the Thaumarchaeota, accounting for 65 % of clones, although their diversity was low. A total of 112 tRFLP profiles were generated from 56 samples from 25 subplots; the patterns for both SSU rRNA and mcrA showed little variation between sites, either with plant treatment or with the growing season. Overall these results suggest that wetland soil archaeal populations were resilient to changes in the associated surface plant communities. The work also revealed the presence of novel, mesophilic Thaumarchaeota of unknown metabolic function. 相似文献
77.
Impacts of rising air temperatures and emissions mitigation on electricity demand and supply in the United States: a multi-model comparison 总被引:2,自引:2,他引:0
78.
T. P. M. Goumans Adrian Wander C. Richard A. Catlow Wendy A. Brown 《Monthly notices of the Royal Astronomical Society》2007,382(4):1829-1832
The specific catalytic effect of a silica grain on the formation of methanol via the sequential addition of H atoms to CO adsorbed on the surface is investigated. A negatively charged defect on a siliceous edingtonite surface is found to reduce the gas phase barriers for the H + COads and H + H2 C=Oads reactions by 770 and 399 K, respectively, when compared to the same reactions in the gas phase. The catalytic effect of negatively charged surface sites could also be applicable to the hydrogenation of other adsorbed unsaturated species. However, the activation energies on the surface defect are still too large (1150 and 2230 K) for CH3 OH to form efficiently at 10–20 K in the interstellar medium via a classical mechanism. It is therefore suggested that quantum mechanical tunnelling through the activation barrier is required for these hydrogen addition reactions to proceed at such temperatures. The calculations show that because the adsorption energies of CO and H2 C=O on the negatively charged defect are substantial, CH3 OH may form efficiently during the warm-up period in star-forming regions. 相似文献
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