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121.
Christina E. Jonsson Gunhild C. Rosqvist Melanie J. Leng Christian Bigler Jonas Bergman Päivi Kaislahti Tillman Hilary J. Sloane 《第四纪科学杂志》2010,25(6):918-930
Waters from high‐altitude alpine lakes are mainly recharged by meteoric water. Because of seasonal variations in precipitation and temperature and relatively short hydraulic residence times, most high‐altitude lakes have lake water isotopic compositions (δ18Olake) that fluctuate due to seasonality in water balance processes. Input from snowmelt, in particular, has a significant role in determining lake water δ18O. Here we compare two high‐resolution δ18Odiatom records from lake sediments in the Swedish Scandes with instrumental data from the last century obtained from nearby meteorological stations. The time period AD 1900–1990 is characterised by an increase in winter precipitation and high winter/summer precipitation ratios and this is recorded in δ18Odiatom as decreasing trends. Lowest δ18Odiatom values and highest amount of winter precipitation are found around AD 1990 when the winter North Atlantic Oscillation index was above +2. We conclude that for the last 150 a the main factor affecting the δ18Odiatom signal in these sub‐Arctic high‐altitude lakes with short residence times has been changes in amount of winter precipitation and that δ18Odiatom derived from high‐altitude lakes in the Swedish Scandes can be used as a winter precipitation proxy. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
122.
Rhys Whitley Daniel Taylor Catriona Macinnis‐Ng Melanie Zeppel Isa Yunusa Anthony O'Grady Ray Froend Belinda Medlyn Derek Eamus 《水文研究》2013,27(8):1133-1146
A modified Jarvis–Stewart model of canopy transpiration (Ec) was tested over five ecosystems differing in climate, soil type and species composition. The aims of this study were to investigate the model's applicability over multiple ecosystems; to determine whether the number of model parameters could be reduced by assuming that site‐specific responses of Ec to solar radiation, vapour pressure deficit and soil moisture content vary little between sites; and to examine convergence of behaviour of canopy water‐use across multiple sites. This was accomplished by the following: (i) calibrating the model for each site to determine a set of site‐specific (SS) parameters, and (ii) calibrating the model for all sites simultaneously to determine a set of combined sites (CS) parameters. The performance of both models was compared with measured Ec data and a statistical benchmark using an artificial neural network (ANN). Both the CS and SS models performed well, explaining hourly and daily variation in Ec. The SS model produced slightly better model statistics [R2 = 0.75–0.91; model efficiency (ME) = 0.53–0.81; root mean square error (RMSE) = 0.0015–0.0280 mm h‐1] than the CS model (R2 = 0.68–0.87; ME = 0.45–0.72; RMSE = 0.0023–0.0164 mm h‐1). Both were highly comparable with the ANN (R2 = 0.77–0.90; ME = 0.58–0.80; RMSE = 0.0007–0.0122 mm h‐1). These results indicate that the response of canopy water‐use to abiotic drivers displayed significant convergence across sites, but the absolute magnitude of Ec was site specific. Period totals estimated with the modified Jarvis–Stewart model provided close approximations of observed totals, demonstrating the effectiveness of this model as a tool aiding water resource management. Analysis of the measured diel patterns of water use revealed significant nocturnal transpiration (9–18% of total water use by the canopy), but no Jarvis–Stewart formulations are able to capture this because of the dependence of water‐use on solar radiation, which is zero at night. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
123.
124.
Challenges of analyzing multi-hazard risk: a review 总被引:9,自引:6,他引:3
Melanie S. Kappes Margreth Keiler Kirsten von Elverfeldt Thomas Glade 《Natural Hazards》2012,64(2):1925-1958
Many areas of the world are prone to several natural hazards, and effective risk reduction is only possible if all relevant threats are considered and analyzed. However, in contrast to single-hazard analyses, the examination of multiple hazards poses a range of additional challenges due to the differing characteristics of processes. This refers to the assessment of the hazard level, as well as to the vulnerability toward distinct processes, and to the arising risk level. As comparability of the single-hazard results is strongly needed, an equivalent approach has to be chosen that allows to estimate the overall hazard and consequent risk level as well as to rank threats. In addition, the visualization of a range of natural hazards or risks is a challenging task since the high quantity of information has to be depicted in a way that allows for easy and clear interpretation. The aim of this contribution is to give an outline of the challenges each step of a multi-hazard (risk) analysis poses and to present current studies and approaches that face these difficulties. 相似文献
125.
Holger Class Anozie Ebigbo Rainer Helmig Helge K. Dahle Jan M. Nordbotten Michael A. Celia Pascal Audigane Melanie Darcis Jonathan Ennis-King Yaqing Fan Bernd Flemisch Sarah E. Gasda Min Jin Stefanie Krug Diane Labregere Ali Naderi Beni Rajesh J. Pawar Adil Sbai Sunil G. Thomas Laurent Trenty Lingli Wei 《Computational Geosciences》2009,13(4):409-434
126.
Isotope Dilution Determinations of Lu,Hf, Zr,Ta and W,and Hf Isotope Compositions of NIST SRM 610 and 612 Glass Wafers 总被引:1,自引:0,他引:1
Oliver Nebel Melanie L.A. Morel Pieter Z. Vroon 《Geostandards and Geoanalytical Research》2009,33(4):487-499
Isotope dilution determinations of Lu, Hf, Zr, Ta and W are reported for nine test portions (five for W) of NIST SRM 610 and 612 glass wafers. Additionally, all test portions were analysed for their Hf isotope compositions. In general, high field strength elemental (HFSE) distributions in NIST SRM 610 and 612 were reproducible to ~± 1%, except for Zr (± 5%) in NIST SRM 612, and absolute reported concentrations agreed with previously published values, but with higher precision. The slightly worse reproducibility of Zr in NIST SRM 612 compared to other HFSE is interpreted to result from analytical scatter, rather than sample inhomogeneity. The analyses demonstrated elemental homogeneity for both glass wafers for samples of 1–2 mg with respect to the precision of the method, i.e., ± 1% or better. Average Hf isotope compositions for both glass wafers agreed within uncertainty and the weighted average of all determinations yielded a mean 176Hf/177Hf ratio of 0.282111 ± 0.000009 (95% confidence level). However, although mean values for NIST SRM 610 and 612 agreed within analytical limits, NIST SRM 610 test portions showed a tendency of systematically elevated isotope composition of ~ 0.5 ?Hf units when compared to NIST SRM 612, which may indicate a slightly more radiogenic Hf isotope composition of NIST SRM 610. The results of this study suggest that NIST SRM 610 and 612 are valuable calibrators for HFSE in situ analyses within the given uncertainties. 相似文献
127.
Locating benefits: Decision-spaces, resource access and equity in US community-based forestry 总被引:1,自引:0,他引:1
Melanie Hughes McDermott 《Geoforum》2009,40(2):249-259
In the US, the Ford Foundation’s Community-based Forestry Demonstration Program (2000-2005) promoted an internationally prominent model of community forestry centered on the simultaneous, balanced pursuit of ecological, economic and social goals (often symbolized as the “three-legged stool,” or “triple bottom line”). This paper develops an alternative framework for analysis that emphasizes the causal precedence of shifts in power relations, specifically the devolution of resource access and decision-making authority, rather than environmental, social and economic outcomes. These outcomes are not necessarily beneficial, and any benefits realized seldom occur simultaneously. Rather, they can be envisioned as the floors of a house erected sequentially on a foundation of resource access and control. While no universal claim is made, the “house” model proves an apt fit for many community-based forestry initiatives, including the two case studies presented. Who among the differentiated social groups within a community gained access to resources and decision-making influence largely predicted who gained individually. Nonetheless, indirect benefits felt at community and higher scales were significant. The findings further indicate that community forestry generally will not advance social equity unless it specifically targets marginalized groups. Crucially, equity is understood to embrace not only distributional justice, but also capacity-building and empowerment. 相似文献
128.
Dominic A. Hodgson Elie Verleyen Wim Vyverman Koen Sabbe Melanie J. Leng Matthew D. Pickering Brendan J. Keely 《Quaternary Science Reviews》2009,28(25-26):2689-2696
In this paper we present geological evidence from the Larsemann Hills (Lambert Glacier – Amery Ice Shelf region, East Antarctica) of marine sediments at an altitude of c. 8 m a.s.l., as revealed by diatom, pigment and geochemical proxies in a lake sediment core. The sediments yielded radiocarbon dates between c. 26 650 and 28 750 14C yr BP (31 366–33 228 cal yr BP). This information can be used to constrain relative sea level adjacent to the Lambert Glacier at the end of Marine Isotope Stage 3. These data are compared with the age and altitude of Marine Isotope Stage 3 marine deposits elsewhere in East Antarctica and discussed with reference to late Quaternary ice sheet history and eustatic sea-level change. 相似文献
129.
Minnie Y. Mao Melanie Johnston-Hollitt Jamie B. Stevens Simon J. Wotherspoon 《Monthly notices of the Royal Astronomical Society》2009,392(3):1070-1079
Using radio data at 1.4 GHz from the Australia Telescope Compact Array (ATCA), we identify five head–tail (HT) galaxies in the central region of the Horologium–Reticulum Supercluster (HRS). Physical parameters of the HT galaxies were determined along with substructure in the HRS to probe the relationship between environment and radio properties. Using a density enhancement technique applied to 582 spectroscopic measurements in the 2°× 2° region about A3125/A3128, we find all five HT galaxies reside in regions of extremely high density (>100 galaxies Mpc−3 ). In fact, the environments surrounding HT galaxies are statistically denser than those environments surrounding non-HT galaxies and among the densest environments in a cluster. Additionally, the HT galaxies are found in regions of enhanced X-ray emission and we show that the enhanced density continues out to substructure groups of 10 members. We propose that it is the high densities that allow ram pressure to bend the HT galaxies as opposed to previously proposed mechanisms relying on exceptionally high peculiar velocities. 相似文献
130.
Interpreting flash flood palaeoflow parameters from antidunes and gravel lenses: An example from Montserrat,West Indies
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The wavelength of stationary water‐surface waves and their associated antidune bedforms are related to the mean velocity and depth of formative flow. In past published sand‐bed flume experiments, it was found that lens structures were preserved during antidune growth and change, and the dimension of the lenses was empirically related to antidune wavelength, and thus could be used to estimate flow velocity and depth. This study is the first to compare observations of formative flow conditions and resulting sedimentary structures in a natural setting, testing the previously published relationship at a field‐scale. Trains of stationary and upstream migrating water‐surface waves were prevalent during the flash flood in October 2012 in the Belham Valley, Montserrat, West Indies. Wave positions and wavelengths were assessed at 900 sec intervals through the daylight hours of the event within a monitored reach. The wave data indicate flow depths up to 1·3 m and velocity up to 3·6 m sec?1. Sedimentary structures formed by antidune growth and change were preserved in the event deposit. These structures include lenses of clast‐supported gravel and massive sand, with varying internal architecture. The lenses and associated low‐angle strata are comparable to sand‐bed structures formed from stationary and upstream migrating waves in flume experiments, confirming the diagnostic value of these structures. Using mean lens length in the event deposit underestimated peak flow conditions during the flood and implied that the lenses were preserved during waning flow. 相似文献