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1.
Biogeomorphology adds the element “biological dynamics” (of populations or communities) to chemical and physical geomorphic factors and thus complicates the framework of geomorphic processes. Such biological complications of the animal-induced transport of solids in streams should be particularly important in crayfish, as crayfish affect this transport through their overall activity and intraspecific aggression levels, which could be modified by shelter availability or the establishment of dominance hierarchies among individuals not knowing each other. Using experimental streams, we tested these hypotheses by measuring how shelter availability or residential crayfish group invasion by unknown individuals affected the impact of the crayfish Orconectes limosus on the (i) transport of gravel at baseflow (during 12 experimental days); (ii) sediment surface characteristics (after 12 days); and (iii) critical shear stress causing incipient gravel motion during simulated floods (after 12 days). The two potentially important factors shelter availability or residential group invasion negligibly affected the crayfish impact on gravel sediments, suggesting that habitat unfamiliarity (a third potentially important factor affecting crayfish activity) should increase the crayfish-induced sediment transport. Because habitat unfamiliarity is associated with sporadic long-distance migrations of a few crayfish individuals, this third factor should play a minor role in real streams, where crayfish biomass should be a key factor in relations with crayfish effects on sediments. Therefore, we combined the results of this study with those of previous crayfish experiments to assess how crayfish biomass could serve in modelling the gravel transport. Crayfish biomass explained 47% of the variability in the baseflow gravel transport and, in combination with the coefficient of variation of the bed elevation and algal cover, 72% of the variability in the critical gravel shear stress. These results encourage more research on the topic, as an increasing number of eliminations of abiotic and biotic factors that could complicate the animal-induced sediment transport in streams would facilitate the use of biological variables (e.g., bioturbator biomass) in future modelling of the transport of solids. 相似文献
2.
Yoichi Fukuda Toshihiro Higashi Shuzo Takemoto Maiko Abe Sjafra Dwipa Dendi Surya Kusuma Achmad Andan Koichiro Doi Yuichi Imanishi Giuseppe Arduino 《Journal of Geodynamics》2004,38(3-5):489
For the purposes of the calibration of the superconducting gravimeter (SG) in Bandung and the establishment of the absolute gravity (AG) points, we carried out AG measurements for the first time in Indonesia in November 2002. The measurements in Bandung were conducted between November 15th and 20th by means of a FG5 (#210), and 14,520 effective drops were obtained. The gravity value newly determined at the AG point in Bandung is 977976701.2 μgal (1 μgal = 10−8 ms−2) and the scale factor for the SG is −52.22 μgal/V. We also established another AG point in Yogyakarta near Merapi volcano and carried out AG measurements in Yogyakarta between November 22nd and 26th. The gravity value determined for this station is 978203093.5 μgal. 相似文献
3.
Sébastien Joannin Franck Bassinot Nathalie Combourieu Nebout Odile Peyron Célia Beaudouin 《Quaternary Science Reviews》2011,30(3-4):280-297
The ODP leg 161 Site 976 (Alboran Sea) is a deep-sea section sampled at a water depth of 1108 m in the Western Mediterranean Sea. Pollen analysis provides a vegetation and climate record of the Mid Pleistocene Transition (MPT), roughly one million years ago. The age-model tied to biostratigraphic events was revised by aligning the pollen climate index (PCI) to Mediterranean (KC01b) and global (LR04) oxygen isotope records. The studied time slice spans the interval ~1.09 Ma (MIS 31) to ~0.90 Ma (MIS 23).Across this interval, past phytogeography of nowadays extinct taxa, which were rare, allows a successful application of the modern analogues technique (MAT) to quantitative climate reconstructions for the MPT. Five, long-term, obliquity-related vegetation successions (O1 to O5), and eight short-term, precession-related vegetation successions (P1 to P8) are observed within the studied interval. These vegetation successions, regardless of their duration, show the same pattern: the progressive replacement of temperate trees by mountainous taxa, and then by herbs and steppe maxima. Precession-related successions correspond, therefore, to as dramatic vegetation changes as those driven by obliquity, including a final steppe phase under deteriorated climate conditions.Wavelet analysis of the PCI record shows that the Western Mediterranean experienced a shift at 1.01 Ma from precession-dominated frequencies (1.05–1.01 Ma) to obliquity-dominated frequencies (1.01–0.9 Ma). There is, therefore, an apparent discrepancy between wavelet analysis results and vegetation dynamic analysis (which suggests that obliquity and precession are recorded throughout the entire studied interval). This discrepancy could result from the fact that the PCI record sums, somehow, similar vegetation changes (wet to dry) occurring at different periodicities. Such a complex vegetation dynamics is mathematically rendered through a single parameter (i.e. principal component), which does not successfully catch the subtle combinations of variability occurring at two close periodicities. Furthermore, the pollen-inferred Early Pleistocene vegetation dynamic (and climate) of the Western Mediterranean region does not show a decrease of the obliquity response relative to the precession response at the onset of the MPT. 相似文献
4.
Vertical velocity field in the convective boundary layer as observed with an acoustic Doppler sodar 总被引:1,自引:0,他引:1
The morning development of the daytime convective boundary layer (CBL) during fine weather has been observed with an acoustic Doppler sodar of the C.R.P.E. In particular, the vertical profile of the vertical velocity third-order statistic W*
3 has been obtained. This quantity is a maximum near 0.3z
I where z
I, is the height of the CBL. The histogram of vertical velocity in the CBL shows a relationship between W
3 and the convective velocity W
* and is useful for convective plume determination. 相似文献
5.
The vertical velocity field and the convective plumes in the atmospheric boundary layer have been observed during morning hours with the acoustic Doppler sounder of the C.R.P.E. A method for plume determination using acoustic soundings in the well-mixed layer is presented. Using Telford's 1970 and Manton's 1975 models, a comparison is made between the predictions of the models and the plume properties as observed by the Doppler sodar. The mean plume velocity is found to be parabolic. It is shown, restricting Monin and Obukhov similarity to conditions inside plumes and using only vertical velocity within plumes, that the observed convective plumes carry nearly sixty percent of the sensible heat flux at the top of the surface layer. 相似文献
6.
Emmanuelle Montarges-Pelletier Laurent Jeanneau Pierre Faure Isabelle Bihannic Odile Barres Bruno S. Lartiges 《Environmental Geology》2007,53(1):85-102
The Moselle river flows in the north-east of France, from Vosges Mountains to neighboring countries Luxembourg and Germany.
One of its tributaries, the Fensch river, drains a highly industrialized watershed, strongly impacted by mining, smelting
and surfacing activities. The objective of this work, part of a general research program on Moselle watershed (Zone Atelier
Moselle) was to assess the impact of the polluted Fensch river on the global quality of the Moselle river. For that purpose,
water, sediments and suspended particulate matter were sampled in both rivers, upstream and downstream the junction. Four
main sampling campaigns were carried out, in winter during a flood event and in spring at low water level. On a first step,
mineralogical analyses (XRD and FTIR) and chemical analyses (ICP-MS, ICP-AES), were performed on sediments, suspended particulate
matters and filtered waters. Major and trace elements concentrations were obtained on two different granulometric fractions
(0–2 mm and 0–50 μm) revealing the enrichment in heavy metals of fine particles. From one collecting campaign to another,
seasonal variations could be evidenced on suspended matter composition even though major minerals (calcite, quartz and kaolinite)
were always present. Furthermore, spatial variations were evidenced for Fensch and Moselle downstream sediments. Thus, very
fine-grained sediments, poorly crystallized, displaying at the same time higher metal concentrations and higher organic matter
content than in Fensch river material, were collected downstream, in a low hydrodynamic conditions zone, assumed as a preferential
sedimentary zone or even as a placer. Strong correlations could be revealed between iron content and contaminant concentrations,
confirming the origin of polluted material. 相似文献
7.
The binational cities of Dover and Calais and their region 总被引:2,自引:0,他引:2
Odile Heddebaut 《GeoJournal》2001,54(1):61-71
This paper analyses the question of cities that are localised at each part of an international border. We take as an example
the two cities of Dover and Calais and look at if they can be considered as binational cities, because they have been recently
connected by a tunnel, the ‘fixed link’, and because since 1993, the inner state borders of the European Union have disappeared.
It determines firstly if these two towns have been brought closer by the construction of the Channel tunnel and if specific
ties are linking these two towns. The article scrutinizes actions taken under INTERREG funds under the general framework of
the creation of the ‘Transmanche Region’ and its extension towards a Euroregion to sort out these two cities joint involvement.
Finally, it checks if this new area could lead to cross-border activity either for work or tourism and leisure purposes that
could conduct the cities of Dover and Calais toward a new type of relationship, premises of a binational city.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Michel Magny Odile Peyron Laura Sadori Elena Ortu Giovanni Zanchetta Boris Vannière Willy Tinner 《第四纪科学杂志》2012,27(3):290-296
Pollen‐based quantitative estimates of seasonal precipitation from Lake Pergusa and lake‐level data from Lake Preola in Sicily (southern Italy) allow three successive periods to be distinguished within the Holocene: an early Holocene period before ca. 9800 cal a BP with rather dry climate conditions in winter and summer, a mid‐Holocene period between ca. 9800 and 4500 cal a BP with maximum winter and summer wetness, and a late Holocene period after 4500 cal a BP with declining winter and summer wetness. This evolution observed in the south‐central Mediterranean shows strong similarities to that recognized in the eastern Mediterranean. But, it contrasts with that reconstructed in north‐central Italy, where the mid‐Holocene appears to be characterized by a winter (summer) precipitation maximum (minimum), while the late Holocene coincided with a decrease (increase) in winter (summer) precipitation. Maximum precipitation at ca. 10 000–4500 cal a BP may have resulted from (i) increased local convection in response to a Holocene insolation maximum at 10 000 cal a BP and then (ii) the gradual weakening of the Hadley cell activity, which allowed the winter rainy westerlies to reach the Mediterranean area more frequently. After 4500 cal a BP, changes in precipitation seasonality may reflect non‐linear responses to orbitally driven insolation decrease in addition to seasonal and inter‐hemispheric changes of insolation. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献