Diel variation in immigration of fishes and decapod crustaceans to artificial seagrass habitat     

Susan M. Sogard  Kenneth W. Able 《Estuaries and Coasts》1994,17(3):622-630

Fish and decapod entry into small (1.5 m²) artificial seagrass habitats positioned on an open sand area in a New Jersey estuary was examined to determine if immigration varied between day and night. To encounter the structured habitats, colonizers had to cross an expanse of bare sand, with its presumably higher predation risk. Contrasts in abundance in the artificial seagrass plots between dawn and dusk indicated higher nighttime immigration for four species, including the fishesFundulus heteroclitus andMyoxocephalus aenaeus, and the caridean shrimpsPalaemonetes vulgaris andHippolyte pleuracanthus. Size-frequency distributions of colonizers varied between day and night for two fish species,Menidia menidia andSyngnathus fuscus, with a greater proportion of smaller individuals immigrating to the artificial seagrass at night.Callinectes sapidus also displayed a diel contrast in size distribution but, for this species, proportionately more small individuals colonized the plots during the day. We suggest that diel variability in predation risk and/or diel patterns in motor activity may be responsible for these patterns in immigration.  相似文献   

Solar signals in global climatic change     

Christian-D. Schönwiese  Rolf Ullrich  Frank Beck  Jörg Rapp 《Climatic change》1994,27(3):259-281

Based on the physical background that varying solar activity should lead to variations of the ‘solar constant’ and that the climate system may respond sensitively even to small solar variations, a correlation analysis is performed where hemispheric and global averages of the annual mean surface air temperature are compared with the variations of a variety of solar forcing parameters: sunspots, related hypotheses including variations of the quasi-eleven-year solar cycle length, solar diameter variations and gravitational effects. This analysis is based on the 1881–1988 period, for the northern hemisphere including proxy data 1671–1988. Cross correlations and correlations moving in time reveal some instability effects which are hard to interpret. The temperature variance components which may be hypothetically explained by solar forcing are small. Similarly, a seasonal and regional signal and signal-to-noise analysis based on a gridded temperature time series 1890–1985 reveals small signals which do not exceed roughly 1.5 K in the arctic winter (maximum) or 0.2-0.3 K on a global average.  相似文献   

Measuring the effect of overgrazing in the Sonoran Desert   总被引：4，自引：0，他引：4  

Nevin A. Bryant  Lee F. Johnson  Anthony J. Brazel  Robert C. Balling  Charles F. Hutchinson  Louisa R. Beck 《Climatic change》1990,17(2-3):243-264

Long term overgrazing in Mexico has caused a sharp discontinuity in vegetative cover along the international border in the semi-arid Sonoran Desert. The United States side, protected from overgrazing by the Taylor Act since 1934, exhibits longer, more plentiful grasses and less bare soil than adjoining Mexican lands. Satellite- and ground-based datasets were used in a multi-scale examination of the differential radiative and reflective characteristics of the two regimes. The more exposed Mexican landscape dries more rapidly than the United States following summer convective precipitation. After about three days, depletion of soil moisture evokes a period of higher surface and air temperatures in Mexico. Good correspondence was found between remote and in situ measures of surface temperature and biomass.  相似文献   

A Ground Water Monitoring Study for Pesticides and Nitrates Associated with Golf Courses on Cape Cod     

Stuart Z. Cohen  Susan Nickerson  Robert Maxey  Aubry Dupuy Jr.  Joseph A. Senita 《Ground Water Monitoring & Remediation》1990,10(1):160-160

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Environmental and engineering effects of Sinkholes—the processes behind the problems   总被引：1，自引：1，他引：1  

Barry F. Beck 《Environmental Geology》1988,12(2):71-78

Karstic erosion of the land surface is controlled by processes occurring in the epikarstic zone—the upper portion of the limestone which is most intensely dissolved. Sinkholes developing today are generally the effects of downward movement of mantling sediment into the major karren shafts which drain the epikarstic zone deeper into the true karstic aquifer. Dissolution of the limestone itself does not cause significant changes in man's time frame. The downward erosion of mantling sediment is termed ravelling. Only in uniform sediment will an arched cavity occur. In unconsolidated sediment which is stratified, lateral tunnelling may even occur. Only the major karren can transmit sediment downward, the majority are ineffective. In mantled karst the location of surficial depressions and photo-linears does not necessarily correlate to areas of new collapse. The irregular and highly dissolved character of the epikarstic zone complicates foundation engineering. Downward drainage through this zone may be limited and cause flooding. An understanding of processes in the epikarstic zone is essential in developing on karst. This article was presented as a keynote address at the 21st meeting of the International Association of Hydrogeologists in Guilin, China, October, 1988.  相似文献   

Making management procedures operational innovations implemented in South Africa   总被引：1，自引：0，他引：1  

Plaganyi  Eva E.; Rademeyer  Rebecca A.; Butterworth  Doug S.; Cunningham  Carryn L.; Johnston  Susan J. 《ICES Journal of Marine Science》2007,64(4):626-632

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The AD 1717 rock avalanche deposits in the upper Ferret Valley (Italy): a dating approach with cosmogenic 10Be     

Naki Akçar  Philip Deline  Susan Ivy‐Ochs  Vasily Alfimov  Irka Hajdas  Peter W. Kubik  Marcus Christl  Christian Schlüchter 《第四纪科学杂志》2012,27(4):383-392

On 12 September AD 1717, a rock volume larger than 10 million m³ collapsed onto the Triolet Glacier, mobilized a mass composed of ice and sediment and travelled more than 7 km downvalley in the upper Ferret Valley, Mont Blanc Massif (Italy). This rock avalanche destroyed two small settlements, causing seven casualties and loss of livestock. No detailed maps were made at the time. Later investigators attributed accumulations of granitic boulders and irregular ridges on the upper valley floor to either glacial deposition, or the AD 1717 rock avalanche, or a complex mixture of glacial deposition, earlier rock avalanche and AD 1717 rock avalanche origin. In this study, we present cosmogenic ¹⁰Be exposure ages from nine boulders in the extensive chaotic boulder deposit with irregular ridges, two from Holocene glacier‐free areas, and one from a Little Ice Age moraine. Exposure ages between 330 ± 23 and 483 ± 123 a from eight of nine boulders from the chaotic deposit indicate that at least seven were deposited by the AD 1717 rock avalanche. The other three boulders yielded ¹⁰Be exposure ages of 10 900 ± 400, 9700 ± 400 and 244 ± 97 a, respectively. Our results are in good agreement with the existing chronology from dendrochronology and lichenometry, and radiocarbon analysis of wood samples, but not with older ¹⁴C ages from a peat bog in the upper part of the valley. Based on the new age control, the rock avalanche deposits cover the whole bottom of the upper Ferret valley. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Particle Acceleration at Comet Related Shock Surfaces     

Susan M.P. McKenna-Lawlor  E. Kirsch  P. Daly 《Astrophysics and Space Science》1998,264(1-4):545-566

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Glacial Deposition Along an Ice-Contact Slope: An Example from the Southern Lake District, Chile   总被引：1，自引：0，他引：1  

Susan E. Turbek  & Thomas V. Lowell 《Geografiska Annaler: Series A, Physical Geography》1999,81(2):325-346

Glacially derived sediments and structures vary systematically with topographic position along ice-contact slopes near the margin of former temperate piedmont glaciers in the southern Lake District, Chile. Features along lower positions of the slopes include glaciolacustrine sediments and large-scalethrusting. Middle slope features include low-angle subglacial thrusting of thin slices of lacustrine sediment. Upper slope features include high-angle thrusting, and lodgement and flow till. Locally, the same ordering of these features occurs in vertical sequence.
A common theme that unifies the processes represented by these features is the distribution of hydrostatic pressure. Thicker ice (producing higher glacier overburden pressures) and aquicludes of fine-grained sediments toward the center of the basin result in high hydrostatic pressures, whereas thin ice and porous out-wash reduce these pressures at the top of the ice-contact slopes.However, such a distribution cannot completely explain the observed vertical sequences; hence, local variations in hydrostatic pressure because of lithologic contrasts probably play a role. Nowhere along the ice-contact slope are pervasively deformed glacial sediments observed; therefore they cannot be invoked to explain the low glacier profiles of these piedmont glacier lobes.  相似文献   

Exploration potential of Cu isotope fractionation in porphyry copper deposits   总被引：6，自引：0，他引：6  

Ryan Mathur  Spencer TitleyFernando Barra  Susan BrantleyMarc Wilson  Allison PhillipsFrancisco Munizaga  Victor MaksaevJeff Vervoort  Garret Hart 《Journal of Geochemical Exploration》2009

We examined the copper isotope ratio of primary high temperature Cu-sulfides, secondary low temperature Cu-sulfides (and Cu-oxides) as well as Fe-oxides in the leach cap, which represent the weathered remains of a spectrum of Cu mineralization, from nine porphyry copper deposits. Copper isotope ratios are reported as δ⁶⁵Cu‰ = ((⁶⁵Cu/⁶³Cu_sample/⁶⁵Cu/⁶³Cu_{NIST 976 standard}) − 1) ? 10³. Errors for all the analyses are ± 0.14‰ (determined by multiple analyses of the samples) and mass bias was corrected through standard-sample-standard bracketing. The overall isotopic variability measured in these samples range from − 16.96‰ to 9.98‰.  相似文献