Hydrogeologic controls on streamflow sensitivity to climate variation     

Anne Jefferson  Anne Nolin  Sarah Lewis  Christina Tague 《水文研究》2008,22(22):4371-4385

Climate models project warmer temperatures for the north‐west USA, which will result in reduced snowpacks and decreased summer streamflow. This paper examines how groundwater, snowmelt, and regional climate patterns control discharge at multiple time scales, using historical records from two watersheds with contrasting geological properties and drainage efficiencies. In the groundwater‐dominated watershed, aquifer storage and the associated slow summer recession are responsible for sustaining discharge even when the seasonal or annual water balance is negative, while in the runoff‐dominated watershed subsurface storage is exhausted every summer. There is a significant 1 year cross‐correlation between precipitation and discharge in the groundwater‐dominated watershed (r = 0·52), but climatic factors override geology in controlling the inter‐annual variability of streamflow. Warmer winters and earlier snowmelt over the past 60 years have shifted the hydrograph, resulting in summer recessions lasting 17 days longer, August discharges declining 15%, and autumn minimum discharges declining 11%. The slow recession of groundwater‐dominated streams makes them more sensitive than runoff‐dominated streams to changes in snowmelt amount and timing. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

The AAT/WFI survey of the Monoceros Ring and Canis Major dwarf galaxy – I. From l= (193–276)°     

Blair C. Conn  Richard R. Lane  Geraint F. Lewis  Rodrigo Gil-Merino  Mike J. Irwin  Rodrigo A. Ibata  Nicolas F. Martin  Michele Bellazzini  Robert Sharp  Artem V. Tuntsov  Annette M. N. Ferguson 《Monthly notices of the Royal Astronomical Society》2007,376(3):939-959

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Limnological and sedimentary processes at Sawtooth Lake,Canadian High Arctic,and their influence on varve formation   总被引：1，自引：0，他引：1  

Pierre Francus  Raymond S. Bradley  Ted Lewis  Mark Abbott  Mike Retelle  Joseph S. Stoner 《Journal of Paleolimnology》2008,40(3):963-985

This paper synthesizes data collected to document the modern limnological and sedimentary processes in South Sawtooth Lake located on northern Ellesmere Island, Nunavut, Canada. Field observations show that the finely laminated sediments deposited in the distal basin are formed by the settling of overflows and interflows, and in rare occasions, by non-erosive hyperconcentrated density flows. Thin-sections of these sediments allowed for the classification of the sedimentary fabrics into six facies, each representing different limnological processes. The sediments in this distal basin are considered to be continuous and annually laminated (varved) based on radioisotope analyses, and both limnological and sedimentological evidence.  相似文献   

Landforms and landscape evolution in the Skardu,Shigar and Braldu Valleys,Central Karakoram     

Yeong Bae Seong  Michael P. Bishop  Andrew Bush  Penny Clendon  Luke Copland  Robert C. Finkel  Ulrich Kamp  Lewis A. Owen  John F. Shroder 《Geomorphology》2009,103(2):251-267

The Central Karakoram, which includes K2 in Pakistan, is one of the most rapidly rising areas on Earth and exhibits complex topography and extreme relief. Impressive valley fills and glacial landforms are present throughout the valleys. The dynamics of landscape evolution of the region are currently not well understood. Consequently, the landforms were mapped and assessed in the Skardu, Shigar, and Braldu valleys, to elucidate the spatio-temporal scale dependencies of surface processes active in the region. These valleys were examined using geomorphic field methods, remote sensing, geomorphometry, and terrestrial cosmogenic nuclides (TCNs) surface exposure dating. The glaciers in this region have oscillated considerably throughout the Late Quaternary, and four glacial stages have been recognized including at least six glacial advances. Surface processes readjusted after glacier retreat, and ubiquitous mass movements and catastrophic landsliding transported material from steep slopes to valley bottoms, while glaciofluvial meltwater and glacier outburst floods redistributed sediment down valley. Glacier geochronology and late Holocene ages of the outburst flood deposits indicate that landscape evolution has been dominated by glaciation and paraglaciation during the late Quaternary.  相似文献   

Probing pulsar winds using inverse Compton scattering     

Lewis Ball  J. G. Kirk 《Astroparticle Physics》2000,12(4):335-349

We investigate the effects of inverse Compton scattering by electrons and positrons in the unshocked winds of rotationally-powered binary pulsars. This process can scatter low energy target photons to produce gamma rays with energies from MeV to TeV. The binary radio pulsars PSR B1259−63 and PSR J0045−73 are both in close eccentric orbits around bright main sequence stars which provide a huge density of low energy target photons. The inverse Compton scattering process transfers momentum from the pulsar wind to the scattered photons, and therefore provides a drag which tends to decelerate the pulsar wind. We present detailed calculations of the dynamics of a pulsar wind which is undergoing inverse Compton scattering, showing that the deceleration of the wind of PSR B1259−63 due to ‘inverse Compton drag' is small, but that this process may confine the wind of PSR J0045−73 before it attains pressure balance with the outflow of its companion star. We calculate the spectra and light curves of the resulting inverse Compton emission from PSR B1259−63 and show that if the size of the pulsar wind nebula is comparable to the binary separation, then the γ-ray emission from the unshocked wind may be detectable by atmospheric Cherenkov detectors or by the new generation of satellite-borne γ-ray detectors such as INTEGRAL and GLAST. This mechanism may therefore provide a direct probe of the freely-expanding regions of pulsar winds, previously thought to be invisible.  相似文献   

GLOBAL IGNORANCE     

Martin W. Lewis 《Geographical review》2000,90(4):603-628

ABSTRACT. Stories exposing the lack of global knowledge among American high school and college students are ubiquitous. But it is not just students who have difficulty navigating a world map. Global ignorance, in fact, is appallingly prevalent even among scholars, journalists, and public intellectuals who write about globalization and world history. Otherwise erudite and insightful authors commit such basic geographical errors that they can only mystify the public. The present article focuses on, but is not limited to, the misconceptions of Benjamin Barber, Thomas L. Friedman, John Gray, David Landes, and Paul Krugman. It further explores the reasons why the debate over globalization, in particular, generates so much nonsense, and it concludes with a call for the revitalization of world geography.  相似文献   

The application of ecohydrological groundwater indicators to hydrogeological conceptual models   总被引：1，自引：0，他引：1  

Lewis J 《Ground water》2012,50(5):679-689

This article reviews the application of ecohydrological indicators to hydrogeological conceptual models for earth-scientists with little or no botanical training. Ecohydrological indicators are plants whose presence or morphology can provide data about the hydrogeological setting. By examining the literature from the fields of ecohydrology, hydrogeology, geobotany, and ecology, this article summarizes what is known about groundwater indicator plants, their potential for providing information about the aquifer, and how this data can be a cost-effective addition to hydrogeological conceptual models. We conclude that the distribution and morphology of ecohydrological groundwater indicator plants can be useful to hydrogeologists in certain circumstances. They are easiest to evaluate in arid and semiarid climates. Ecohydrological groundwater indicators can provide information about the absolute depth to the water table, patterns of groundwater fluctuation, and the mineralization of the aquifer. It is shown that an understanding of the meteorological conditions of a region is often necessary to accurately interpret groundwater indicator plants and that useful data is usually obtained by observing patterns of vegetation behavior rather than interpreting individual plants. The most serious limitations to applying this source of information to hydrogeological conceptual models are the limited data in the literature and the regional nature of many indicator plants. The physical and physiological indications of the plants exist, but little effort has been made to interpret them. This article concludes by outlining several potential lines of research that could further the usefulness of ecohydrological groundwater indicators to the hydrogeological community.  相似文献   

Assessing the additive risks of PSII herbicide exposure to the Great Barrier Reef     

Lewis SE  Schaffelke B  Shaw M  Bainbridge ZT  Rohde KW  Kennedy K  Davis AM  Masters BL  Devlin MJ  Mueller JF  Brodie JE 《Marine pollution bulletin》2012,65(4-9):280-291

Herbicide residues have been measured in the Great Barrier Reef lagoon at concentrations which have the potential to harm marine plant communities. Monitoring on the Great Barrier Reef lagoon following wet season discharge show that 80% of the time when herbicides are detected, more than one are present. These herbicides have been shown to act in an additive manner with regards to photosystem-II inhibition. In this study, the area of the Great Barrier Reef considered to be at risk from herbicides is compared when exposures are considered for each herbicide individually and also for herbicide mixtures. Two normalisation indices for herbicide mixtures were calculated based on current guidelines and PSII inhibition thresholds. The results show that the area of risk for most regions is greatly increased under the proposed additive PSII inhibition threshold and that the resilience of this important ecosystem could be reduced by exposure to these herbicides.  相似文献   

Dynamics of herbicide transport and partitioning under event flow conditions in the lower Burdekin region, Australia     

Davis AM  Lewis SE  Bainbridge ZT  Glendenning L  Turner RD  Brodie JE 《Marine pollution bulletin》2012,65(4-9):182-193

This study examined the temporal variability in herbicide delivery to the Great Barrier Reef (GBR) lagoon (Australia) from one of the GBR catchment's major sugarcane growing regions. Annual loads of measured herbicides were consistently in the order of 200+kg. Atrazine, it's degradate desethylatrazine, and diuron contributed approximately 90% of annual herbicide load, with early 'first-flush' events accounting for the majority of herbicide loads leaving the catchment. Assessment of herbicide water-sediment partitioning in flood runoff highlighted the majority of herbicides were transported in predominantly dissolved form, although a considerable fraction of diuron was transported in particulate-bound form (ca. 33%). Diuron was also the herbicide demonstrating the highest concentrations and frequency of detection in sediments collected from catchment waterways and adjacent estuarine-marine environments, an outcome aligning with previous research. Herbicide physico-chemical properties appear to play a crucial role in partitioning between water column and sediment habitat types in GBR receiving ecosystems.  相似文献   

An assessment of residence times of land-sourced contaminants in the Great Barrier Reef lagoon and the implications for management and reef recovery     

Brodie J  Wolanski E  Lewis S  Bainbridge Z 《Marine pollution bulletin》2012,65(4-9):267-279

We argue that the residence times of key pollutants exported to the Great Barrier Reef (GBR) are greater in the GBR lagoon than those of the water itself, in contradiction to some previous assumptions. Adverse effects of the pollutant discharge will be greater and longer lasting than previously considered, in turn requiring stronger or more urgent action to remediate land practices. Residence times of fine sediments, nitrogen and phosphorus, pesticides and trace metals are suggested to be from years to decades in the GBR lagoon and highly likely to be greater than the residence time of water, estimated at around 15-365days. The recovery of corals and seagrass in the central region of the GBR following current land-use remediation in the catchment depends on the residence time of these contaminants. Ecohydrological modeling suggests that this recovery may take decades even with adequate levels of improved land management practices.  相似文献