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201.
M. Boyd C. Surette J. Surette I. Therriault S. Hamilton 《Journal of Paleolimnology》2013,50(3):365-377
Whitefish Lake is a large (11-km-long), shallow, basin in Northwestern Ontario, Canada. The presence of extensive stands of wild rice (Zizania sp.) in combination with high archaeological site density suggests that this lake was ecologically important to regional precontact populations. Collection and analysis of sediment from Whitefish Lake was initiated in 2008 in order to reconstruct changes in lake depth, climate, and vegetation throughout the Holocene. In general, the upper 4.5 m of basinal sediment is composed of ~1.5+ m of varves, which is overlain by a 1.5-m-thick unit with ped-like structures, and ~1.5 m of lacustrine sediment. This sequence documents an early proglacial lake phase, followed by a dry interval before 4,300 (4,900 cal) BP when the lake was significantly shallower, and the establishment of the modern lake during the late Holocene. Plant microfossil (phytolith) evidence indicates that wild rice had colonized the basin ~5,300 (6,100 cal) BP as the lake level rose in response to climate change. Beginning ~4,000 (4,500 cal) BP, changes in elemental data suggest a sharp increase in lake productivity and a switch to anaerobic depositional conditions as the rate of organic sedimentation increased. Recent archaeological research confirms that wild rice was locally processed and consumed during the Middle and Late Woodland periods (~300 BC–AD 1700) although it was evidently growing in the lake well before this time. 相似文献
202.
Kim Hanjun Kang Sarah M. Takahashi Ken Donohoe Aaron Pendergrass Angeline G. 《Climate Dynamics》2021,56(1-2):17-27
Climate Dynamics - We investigate the possible causes for inter-model spread in tropical zonal-mean precipitation pattern, which is divided into hemispherically symmetric and anti-symmetric modes... 相似文献
203.
Elizabeth Holcombe Sarah Smith Edmund Wright Malcolm G. Anderson 《Natural Hazards》2012,61(2):351-385
Despite the recognition of the need for mitigation approaches to landslide risk in developing countries, the delivery of ‘on-the-ground’
measures is rarely undertaken. With respect to other ‘natural’ hazards, it is widely reported that mitigation can pay. However,
the lack of such an evidence base in relation to landslides in developing countries hinders advocacy amongst decision makers
for expenditure on ex-ante measures. This research addresses these limitations directly by developing and applying an integrated
risk assessment and cost–benefit analysis of physical landslide mitigation measures implemented in an unplanned community
in the Eastern Caribbean. In order to quantify the level of landslide risk reduction achieved, landslide hazard and vulnerability
were modelled (before and after the intervention), and project costs, direct and indirect benefits were monetised. It is shown
that the probability of landslide occurrence has been substantially reduced by implementing surface-water drainage measures
and that the benefits of the project outweigh the costs by a ratio of 2.7–1. This paper adds to the evidence base that ‘mitigation
pays’ with respect to landslide risk in the most vulnerable communities—thus strengthening the argument for ex-ante measures.
This integrated project evaluation methodology should be suitable for adoption as part of the community-based landslide mitigation
project cycle, and it is hoped that this resource, and the results of this study, will stimulate further such programmes. 相似文献
204.
Sarah Wolf 《Natural Hazards》2012,61(3):1099-1113
The concepts vulnerability and risk are of great importance in the fields of climate change and natural hazards. Confusion
is asserted in the terminology used by the respective communities, and a large conceptual literature has not solved this problem.
This affects the communication within and between the two communities and the comparison of results from vulnerability and
risk assessments. This paper argues that the main difference between methods to assess vulnerability and risk in the climate
and the disaster communities is not a conceptual one, but rather different terminologies are used. This point is made using
a formal framework of vulnerability to climate change that makes the structure of vulnerability and risk assessments explicit.
The framework distinguishes three assessment approaches in the field of vulnerability to climate change, which recur—under
different labels—in the risk assessment approaches analysed. While within each community, the same terms are ambiguously used
to refer to more than one assessment approach, the confusion is enhanced between the two communities by using different labels
for very similar approaches. As an application of the results, similarities and differences between two assessment tools are
analysed: the Dynamic Interactive Vulnerability Assessment model (DIVA) for the case of vulnerability to climate change and
the CATastrophe SIMulation model (CatSim) for risk of natural hazards. 相似文献
205.
Shoreline armoring is extensive in urban areas worldwide, but the ecological consequences are poorly documented. We mapped
shoreline armoring along the Duwamish River estuary (Washington State, USA) and evaluated differences in temperature, invertebrates,
and juvenile salmon (Oncorhynchus spp.) diet between armored and unarmored intertidal habitats. Mean substrate temperatures were significantly warmer at armored
sites, but water temperature similar to unarmored habitats. Epibenthic invertebrate densities were over tenfold greater on
unarmored shorelines and taxa richness double that of armored locations. Taxa richness of neuston invertebrates was also higher
at unarmored sites, but abundance similar. We did not detect differences in Chinook (O. tshawytscha) diet, but observed a higher proportion of benthic prey for chum (O. keta) from unarmored sites. Given that over 66% of the Duwamish shoreline is armored—similar to much of south and central Puget
Sound—our results underscore the need for further ecological study to address the impacts of estuary armoring. 相似文献
206.
Leesun Kim Ian E. Galbally Nichola Porter Ian A Weeks Sarah J Lawson 《Journal of Atmospheric Chemistry》2011,68(3):265-279
Emissions of biogenic volatile organic compounds (BVOCs) from mechanical wounding of leaves and branches of plants can contribute
to the atmospheric burden of volatile organic compounds (VOCs) in both (a) urban airsheds (from urban garden maintenance)
and (b) the global atmosphere (from large scale forest harvesting). These emissions of BVOCs are poorly understood and quantified,
and their role in urban and global emissions inventories neglected. This paper presents measurements of the magnitude, duration
and composition of emissions of BVOCs, carbon dioxide (CO2) and methane (CH4) from freshly cut leaf mulch and wood chips derived from a common eucalypt tree, Eucalyptus sideroxylon (red ironbark), found in southeastern Australian forests and gardens. The emissions of BVOCs from freshly cut and shredded
leaves and wood of E. sideroxylon were found to be 2.3 ± 0.6 and 0.05 ± 0.04 mg g-1 DM (Dry Mass) from leaf mulch and wood chips respectively and to last typically for 1 day following cutting. Three sampling
techniques were used for VOC speciation and the 12 most abundant BVOCs released from the mulch materials were identified.
The specific BVOCs emitted in order of decreasing abundance from leaf mulch are: (a) stored plant oils, 1,8-cineole, α–pinene
and o-cymene which make up the major part of the emissions, (b) a minor contribution from chemicals associated with environmental
stress and wound defence, (Z)–3–hexenyl acetate, (E)-2-hexenal and (Z)-3-hexen-1-ol, and (c) a second minor contribution from
metabolic products, acetaldehyde and acetone. The observed integrated emissions of BVOCs from leaves following mulching are
equivalent to more than half and perhaps all of the likely stored plant oils in the leaves. For the two comparable studies
available, one of a plant with stored oils (this study) and one of a plant without stored plant oils, the emissions of leaf
wound defence BVOCs are in the same range for both plants. In the plant with stored plant oils, the plant oil emissions are
about a factor of 11 larger in emission rate than the plant wound defence BVOCs. A compilation of available leaf wounding
BVOC emission studies indicates that for plants with stored plant oils, plant oil emissions dominate, whereas with other plants,
leaf wound defence BVOCs dominate the emissions. 相似文献
207.
Stratospheric circulation in seasonal forecasting models: implications for seasonal prediction 总被引:1,自引:1,他引:0
Amanda C. Maycock Sarah P. E. Keeley Andrew J. Charlton-Perez Francisco J. Doblas-Reyes 《Climate Dynamics》2011,36(1-2):309-321
Accurate seasonal forecasts rely on the presence of low frequency, predictable signals in the climate system which have a sufficiently well understood and significant impact on the atmospheric circulation. In the Northern European region, signals associated with seasonal scale variability such as ENSO, North Atlantic SST anomalies and the North Atlantic Oscillation have not yet proven sufficient to enable satisfactorily skilful dynamical seasonal forecasts. The winter-time circulations of the stratosphere and troposphere are highly coupled. It is therefore possible that additional seasonal forecasting skill may be gained by including a realistic stratosphere in models. In this study we assess the ability of five seasonal forecasting models to simulate the Northern Hemisphere extra-tropical winter-time stratospheric circulation. Our results show that all of the models have a polar night jet which is too weak and displaced southward compared to re-analysis data. It is shown that the models underestimate the number, magnitude and duration of periods of anomalous stratospheric circulation. Despite the poor representation of the general circulation of the stratosphere, the results indicate that there may be a detectable tropospheric response following anomalous circulation events in the stratosphere. However, the models fail to exhibit any predictability in their forecasts. These results highlight some of the deficiencies of current seasonal forecasting models with a poorly resolved stratosphere. The combination of these results with other recent studies which show a tropospheric response to stratospheric variability, demonstrates a real prospect for improving the skill of seasonal forecasts. 相似文献
208.
209.
Sarah E. Gasda 《Advances in water resources》2011,34(10):1268-1282
Split-operator methods are commonly used to approximate environmental models. These methods facilitate the tailoring of different approximation approaches to different portions of the differential operator and provide a means to split large coupled problems into pieces that are more amenable to parallel computation than the original fully-coupled problem. However, split-operator methods introduce an additional source of approximation error into the solution, which is typically either ignored or controlled heuristically. In this work, we develop two methods to estimate and control the error in split-operator methods, which lead to a dynamic adjustment of the temporal splitting step based upon the error estimators. The proposed methods are shown to yield robust solutions that provide the desired control of error. In addition, for a typical nonlinear reaction problem, the new methods are shown to reduce the solution error by more than two orders of magnitude compared to standard methods for an identical level of computational effort. The algorithms introduced and evaluated have widespread applicability in environmental modeling. 相似文献
210.
A new tool called ESASS (Enhanced Screen Auger Sampling System) was developed by the U.S. Geological Survey. The use of ESASS, because of its unique U.S. patent design (U.S. patent no. 7,631,705 B1), allows for the collection of representative, depth‐specific groundwater samples (vertical profiling) in a quick and efficient manner using a 0.305‐m long screen auger during hollow‐stem auger drilling. With ESASS, the water column in the flights above the screen auger is separated from the water in the screen auger by a specially designed removable plug and collar. The tool fits inside an auger of standard inner diameter (82.55 mm). The novel design of the system constituted by the plug, collar, and A‐rod allows the plug to be retrieved using conventional drilling A‐rods. After retrieval, standard‐diameter (50.8 mm) observation wells can be installed within the hollow‐stem augers. Testing of ESASS was conducted at one waste‐disposal site with tetrachloroethylene (PCE) contamination and at two reference sites with no known waste‐disposal history. All three sites have similar geology and are underlain by glacial, stratified‐drift deposits. For the applications tested, ESASS proved to be a useful tool in vertical profiling of groundwater quality. At the waste site, PCE concentrations measured with ESASS profiling at several depths were comparable (relative percent difference <25%) to PCE concentrations sampled from wells. Vertical profiling with ESASS at the reference sites illustrated the vertical resolution achievable in the profile system; shallow groundwater quality varied by a factor of five in concentration of some constituents (nitrate and nitrite) over short (0.61 m) distances. 相似文献