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191.
María C. Mateo Sánchez Samuel A. Cushman Santiago Saura 《International journal of geographical information science》2014,28(8):1531-1546
Animals select habitat resources at multiple spatial scales. Thus, explicit attention to scale dependency in species–habitat relationships is critical to understand the habitat suitability patterns as perceived by organisms in complex landscapes. Identification of the scales at which particular environmental variables influence habitat selection may be as important as the selection of variables themselves. In this study, we combined bivariate scaling and Maximum entropy (Maxent) modeling to investigate multiscale habitat selection of endangered brown bear (Ursus arctos) populations in northwest Spain. Bivariate scaling showed that the strength of apparent habitat relationships was highly sensitive to the scale at which predictor variables are evaluated. Maxent models on the optimal scale for each variable suggested that landscape composition together with human disturbances was dominant drivers of bear habitat selection, while habitat configuration and edge effects were substantially less influential. We found that explicitly optimizing the scale of habitat suitability models considerably improved single-scale modeling in terms of model performance and spatial prediction. We found that patterns of brown bear habitat suitability represent the cumulative influence of habitat selection across a broad range of scales, from local resources within habitat patches to the landscape composition at broader spatial scales. 相似文献
192.
In this paper we report an analysis of sampling error uncertainties in mean maximum and minimum temperatures (Tmax and Tmin) carried out on monthly,seasonal and annual scales,including an examination of homogenized and original data collected at 731 meteorological stations across China for the period 1951-2004.Uncertainties of the gridded data and national average,linear trends and their uncertainties,as well as the homogenization effect on uncertainties are assessed.It is shown that the sampling error variances of homogenized Tmax and Tmin,which are larger in winter than in summer,have a marked northwest-southeast gradient distribution,while the sampling error variances of the original data are found to be larger and irregular.Tmax and Tmin increase in all months of the year in the study period 1951-2004,with the largest warming and uncertainties being 0.400℃ (10 yr)-1 + 0.269℃ (10 yr)-1 and 0.578℃ (10 yr)-1 + 0.211℃ (10 yr)-1 in February,and the least being 0.022℃ (10 yr)-1 + 0.085℃ (10 yr)-1 and 0.104℃ (10 yr)-1 +0.070℃ (10 yr)-1 in August.Homogenization can remove large uncertainties in the original records resulting from various non-natural changes in China. 相似文献
193.
The purpose of this study was to evaluate related processes of sediment consolidation and resuspension in a coastal basin and how these processes influence retention of fine sediment delivered by a river diversion. Sediment samples were collected from Lake Lery, a coastal receiving basin of the Caernarvon Diversion from the Mississippi River, Louisiana. Consolidation was tested for six initial sediment concentrations (14.0–105 kg m–3) in a settling column over 15-day periods. Mud erodibility was tested at seven shear stress regimes (0.01–0.60 Pa) using a dual-core Gust erosion microcosm system, on cores containing suspensions that consolidated for 1, 2, and 4 weeks. Consolidation rates were found to be inversely and exponentially related to initial suspension concentration, over concentrations ranging from fluid mud (10–200 kg m–3) to hydraulic dredge effluent. Consolidation is best predicted by a function consisting of two exponential terms and one asymptotic constant, describing rates of rapid initial and slower subsequent settling. Coupled resuspension and consolidation tests (concentrations of 20–21 kg m–3) show that shear stresses generating the highest turbidity peaks increase from ≤0.30 Pa after 2 weeks of consolidation to ≥0.45 Pa after 4 weeks, and this strengthening cannot be attributed solely to increasing sediment concentration over time. Comparison of measured erosion shear stresses with bed shear stresses typical of coastal lakes and bays suggests that this degree of strengthening, if given time to occur, could increase the overall retention of fine sediments deposited on lake and bay floors. 相似文献
194.
This paper investigates whether an inefficient allocation of abatement due to constraints on the use of currently available low carbon mitigation options can promote innovation in new technologies and have a positive impact on welfare. We focus on the case of a nuclear power phase-out and endogenous technical change in energy efficiency and alternative low carbon technologies. The research is inspired by the re-thinking about nuclear power deployment which took place in some countries, especially in Western Europe, after the Fukushima accident in March 2011. The analysis uses an Integrated Assessment Model, WITCH, which features multiple externalities related to greenhouse gas emissions and innovation market failures. Our results show that phasing out nuclear power stimulates R&D investments and deployment of technologies with large learning potential. The resulting technology benefits that would not otherwise occur due to intertemporal and international externalities almost completely offset the economic costs of foregoing nuclear power. The extent of technology benefits depends on the stringency of the climate policy and is distributed unevenly across countries. 相似文献
195.
Vanessa Winchester Martin Sessions Jammie Valdivia Cerda Olaf Wündrich Samuel Clemmens Neil F. Glasser Megan Nash 《Geografiska Annaler: Series A, Physical Geography》2014,96(1):43-59
Glacier Benito is a temperate outlet glacier on the west side of the North Patagonian Icefield. Rates of thinning and ablation were obtained using data collected by the British Joint Services Expedition in 1972/73 and subsequent data collected in 2007 and 2011. Ice‐front recession rates were based on dendrochronological dating for the terminal moraines and aerial and satellite imagery of the ice front in 1944, 1998 and 2002. Between the first Benito survey in 1973 and 2007, the lower glacier thinned by nearly 150 m at an average rate of 4.3 m yr?1 with the rate increasing to 6.1 m yr?1 between 2007 and 2011, a 28.7% increase during the latter period. Increases in ice movement and ablation were negligible: ice movement for 1973 and 2007 averaged 0.45 m day?1 and ablation averaged 0.05 m day?1. Ice front recession along the glacier's centre line from 1886 to 2002 was approximately 1860 m. Retreat rates between 1886 and 1944 averaged 8.9 m yr?1. Thereafter glacier asymmetry makes measurement along the glacier centre line unrepresentative of areal change until 1998 when symmetry was restored; retreat between 1944 and 1998 was 15.4 m yr?1. From 1998 to 2002 the rate increased dramatically to 127.2 m yr?1. Recession from the southern end of Benito's terminal moraine in the 1850s supports an early date for initial retreat of the Icefield's glaciers. 相似文献
196.
Since the early 1960s, the application of aluminum alloy sacrificial anodes to mitigate marine corrosion has been well known. The aim of this work was to study aluminum bioconcentration in Mytilus edulis by an in vitro test performed in two tanks: the first containing non-contaminated water (NCW) and the second containing aluminum-contaminated water (CW) (530 μg L−1) released by sacrificial anode. The mussels were collected and examined over a period of 8 weeks. A comparison between the aluminum concentrations in the digestive glands of mussels from the CW and NCW tanks shows that the highest value (1700 mg/kg d.w.) was found in the CW mussels collected after 13 days. In NCW, the mean aluminum concentration in digestive glands during the test was 281 mg/kg d.w. The rapid concentration decrease in digestive glands is probably due to the inhibition of filtering activity due to valve closure at the high concentration as well as the induction of the detoxification response. 相似文献
197.
Cassandra R. Fenton Reginald L. Hermanns Lars H. Blikra Peter W. Kubik Charlotte Bryant Samuel Niedermann Anette Meixner Mirjam M. Goethals 《Quaternary Geochronology》2011,6(5):437-452
Two rock avalanches in Troms County – the Grøtlandsura and Russenes – were selected as CRONUS-EU natural cosmogenic 10Be production-rate calibration sites because they (a) preserve large boulders that have been continuously exposed to cosmic irradiation since their emplacement; (b) contain boulders with abundant quartz phenocrysts and veins with low concentrations of naturally-occurring 9Be (typically < 1.5 ppb); and (c) have reliable minimum radiocarbon ages of 11,424 ± 108 cal yr BP and 10,942 ± 77 cal yr BP (1σ), respectively. Quartz samples (n = 6) from these two sites contained between 4.28 × 104 and 5.06 × 104 at 10Be/g using the 1.387 Myr 10Be half-life. Determination of these concentrations accounts for topographic and self-shielding, and effects on nuclide production due to isostatic rebound are shown to be negligible. Persistent, constant snow and moss cover cannot be proven, but if taken into consideration they may have reduced 10Be concentrations by 10%. Using the 10Be half-life of 1.387 Myr and the Stone scaling scheme, and accounting for snow- and moss-cover, we calculate an error-weighted mean total 10Be production rate of 4.12 ± 0.19 at/g/yr (1σ). A corresponding error-weighted mean spallogenic 10Be production rate is 3.96 ± 0.16 at/g/yr (1σ), respectively. These are in agreement within uncertainty with other 10Be production rates in the literature, but are significantly, statistically lower than the global average 10Be production rate. This research indicates, like other recent studies, that the production of cosmogenic 10Be in quartz is lower than previously established by other production-rate calibration projects. Similarly, our findings indicate that regional cosmogenic production rates should be used for determining exposure ages of landforms in order to increase the accuracy of those ages. As such, using the total 10Be production rate from our study, we determine an error-weighted mean surface-exposure age of a third rock avalanche in Troms County (the Hølen avalanche) to be 7.5 ± 0.3 kyr (1σ). This age suggests that the rock avalanche occurred shortly after the 8.2 kyr cooling event, just as the radiocarbon ages of the Grøtlandsura and Russenes avalanches confirm field evidence that those rock-slope failures occurred shortly after deglaciation. 相似文献
198.
Terrence Blackburn Samuel A. Bowring Blair Schoene Kevin Mahan Francis Dudas 《Contributions to Mineralogy and Petrology》2011,162(3):479-500
A new approach to U-Pb accessory mineral thermochronology allows high-resolution time-temperature histories to be extracted
from lower crustal xenoliths. The combination of the U-Pb system’s dual decay scheme with the effects of temperature dependent
Pb-diffusion can yield a time sensitive record of Pb production/diffusion within accessory phases. The difference in half-life
for parent isotopes 238U and 235U results in the time-variable production of Pb isotopes 206Pb and 207Pb, while Pb diffusion can result in large variations in the time-scales at which Pb retention occurs between grains of different
sizes. The combined effects of variable production rates between the two systems and diffusion result in data topologies on
a concordia diagram that permit distinction between slow cooling and reheating t-T paths. In slowly cooled systems, the difference
in time for Pb retention for grains of variable size yields a measure of partial retention zone (PRZ) residence time, and
provides a robust measure of cooling rate through the PRZ. In Montana, three lower crustal xenoliths, each from a different
depth, yield U-Pb rutile data that record a prolonged (>1 Ga) and slow cooling history towards a steady state geothermal gradient
following the amalgamation of the terrain onto North America. The shallowest samples record the initial recovery of a conductive
geothermal gradient and cool through the mineral PRZ at rates of <0.25°C/Ma over ~500 Ma. Deeper xenoliths record cooling
at younger times over similar time scales and rates. This multi-depth thermal history provides a long-term record of lithosphere
cooling and stabilization. 相似文献
199.
Tsunamis and intense tropical storms compete as viable mechanisms for catastrophic marine inundations of coastlines, and so
interpretation of deposits laid down by palaeo-events is often problematic. Here, examples are presented from the tropical
South Pacific Islands to demonstrate how indigenous knowledge may provide vital clues supporting sedimentological investigation
and thereby helping to explain the origin of giant boulders emplaced on top of coral reef platforms. 相似文献
200.
Experimental Study of the Brittle Behavior of Clay shale in Rapid Unconfined Compression 总被引:6,自引:3,他引:3
Florian Amann Edward Alan Button Keith Frederick Evans Valentin Samuel Gischig Manfred Blümel 《Rock Mechanics and Rock Engineering》2011,44(4):415-430
The mechanical behavior of clay shales is of great interest in many branches of geo-engineering, including nuclear waste disposal,
underground excavations, and deep well drilling. Observations from test galleries (Mont Terri, Switzerland and Bure, France)
in these materials have shown that the rock mass response near the excavation is associated with brittle failure processes
combined with bedding parallel shearing. To investigate the brittle failure characteristics of the Opalinus Clay recovered
from the Mont Terri Underground Research Laboratory, a series of 19 unconfined uniaxial compression tests were performed utilizing
servo-controlled testing procedures. All specimens were tested at their natural water content with loading approximately normal
to the bedding. Acoustic emission (AE) measurements were utilized to help quantify stress levels associated with crack initiation
and propagation. The unconfined compression strength of the tested specimens averaged 6.9 MPa. The crack initiation threshold
occurred at approximately 30% of the rupture stress based on analyzing both the acoustic emission measurements and the stress–strain
behavior. The crack damage threshold showed large variability and occurred at approximately 70% of the rupture stress. 相似文献