Assessing potential abiotic and biotic complications of crayfish-induced gravel transport in experimental streams     

Bernhard Statzner  Odile Peltret 《Geomorphology》2006,74(1-4):245-256

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   

Atomistic simulation of Mg2SiO4 and Mg2GeO4 spinels: a new model     

M. Blanchard  K. Wright  J. D. Gale 《Physics and Chemistry of Minerals》2005,32(5-6):332-338

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Vegetation response to obliquity and precession forcing during the Mid-Pleistocene Transition in Western Mediterranean region (ODP site 976)     

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   

The First Hop: Use of Beaufort Sea Deltas by Hatch-Year Semipalmated Sandpipers     

Roy T. Churchwell  Steve Kendall  Stephen C. Brown  Arny L. Blanchard  Tuula E. Hollmen  Abby N. Powell 《Estuaries and Coasts》2018,41(1):280-292

River deltas along Alaska’s Beaufort Sea coast are used by hatch-year semipalmated sandpipers (Calidris pusilla) after leaving their terrestrial natal sites, but the drivers of their use of these stopover sites on the first “hop” of fall migration are unknown. We quantified sandpiper temporal distribution and abundance as related to food resources at three river deltas during the beginning of their fall migration (post-breeding period) to compare the habitat quality among these deltas. We conducted population counts, sampled invertebrates, and captured birds to collect blood samples from individuals for triglyceride and stable isotope analyses to determine fattening rates and diet. Patterns of sandpiper and invertebrate abundance were complex and varied among deltas and within seasons. River deltas were used by sandpipers from late July to late August, and peak sandpiper counts ranged from 1000 to 4000 individuals, of which 98% were hatch-year semipalmated sandpipers. Isotopic signatures from blood plasma samples indicated that birds switched from a diet of upland tundra to delta invertebrate taxa as the migration season progressed, suggesting a dependence on delta invertebrates. Despite differences in diet among deltas, we found no differences in fattening rates of juvenile sandpipers as indicated by triglyceride levels. The number of sandpipers was positively associated with abundance of Amphipoda and Oligochaeta at the Jago and Okpilak-Hulahula deltas; an isotopic mixing model indicated that sandpipers consumed Amphipoda and Oligochaeta at Jago, mostly Chironomidae at Okpilak-Hulahula and Spionidae at Canning. Regardless of the difference in sandpiper diets at the Beaufort Sea deltas, their similar fattening rates throughout the season indicate that all of these stopover sites provide a critical food resource for hatch-year sandpipers beginning their first migration.  相似文献   

Storm surge induced flux through multiple tidal passes of Lake Pontchartrain estuary during Hurricanes Gustav and Ike     

Chunyan Li  Eddie Weeks  Brian W. Blanchard 《Estuarine, Coastal and Shelf Science》2010

In September 2008, Hurricanes Gustav and Ike generated major storm surges which impacted the Lake Pontchartrain estuary in Louisiana. This paper presents analyses of in situ measurements acquired during these storm events. The main data used in the analyses were from three bottom mounted moorings equipped with conductivity, temperature, and depth sensors, acoustic Doppler current profilers (ADCPs), and a semi-permanent laterally mounted horizontal acoustic Doppler profiler (ADP). These moorings were deployed in the three major tidal channels that connect Lake Pontchartrain with the coastal ocean. A process similar to tidal straining was observed: the vertical shear of the horizontal velocity was negligible during the inundation stage, but a shear of 0.8 m/s over a less than 5 m water column was recorded during the receding stage, 2–3 times the normal tidal oscillations. The surge reached its peak in the Industrial Canal 1.4–2.1 h before those in the other two channels. The inward flux of water lasted for a shorter time period than that of the outward flux. The inward flux was also observed to have much smaller magnitude than the outward flux (∼960–1200 vs. 2100–3100 million m³). The imbalance was believed to have been caused by the additional water into Lake Pontchartrain through some small rivers and inundation over the land plus rainfall from the hurricanes. The flux through the Industrial Canal was 8–12%, while the flux through the other two tidal passes ranged between 17% and 70% of the total, but mostly split roughly half-half of the remaining (∼88–92% of the total).  相似文献   

Can marine fisheries and aquaculture meet fish demand from a growing human population in a changing climate?     

Gorka Merino  Manuel Barange  Julia L. Blanchard  James Harle  Robert Holmes  Icarus Allen  Edward H. Allison  Marie Caroline Badjeck  Nicholas K. Dulvy  Jason Holt  Simon Jennings  Christian Mullon  Lynda D. Rodwell 《Global Environmental Change》2012,22(4):795-806

Expansion in the world's human population and economic development will increase future demand for fish products. As global fisheries yield is constrained by ecosystems productivity and management effectiveness, per capita fish consumption can only be maintained or increased if aquaculture makes an increasing contribution to the volume and stability of global fish supplies. Here, we use predictions of changes in global and regional climate (according to IPCC emissions scenario A1B), marine ecosystem and fisheries production estimates from high resolution regional models, human population size estimates from United Nations prospects, fishmeal and oil price estimations, and projections of the technological development in aquaculture feed technology, to investigate the feasibility of sustaining current and increased per capita fish consumption rates in 2050. We conclude that meeting current and larger consumption rates is feasible, despite a growing population and the impacts of climate change on potential fisheries production, but only if fish resources are managed sustainably and the animal feeds industry reduces its reliance on wild fish. Ineffective fisheries management and rising fishmeal prices driven by greater demand could, however, compromise future aquaculture production and the availability of fish products.  相似文献   

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  

Odile Taconet  Alain Weill 《Boundary-Layer Meteorology》1982,23(2):133-151

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   

Convective plumes in the atmospheric boundary layer as observed with an acoustic Doppler sodar     

Odile Taconet  Alain Weill 《Boundary-Layer Meteorology》1983,25(2):143-158

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   

The junction of Fensch and Moselle rivers,France; mineralogy and composition of river materials     

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   

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