Landscape and climate change threats to wetlands of North and Central America   总被引：1，自引：1，他引：0  

William J. Mitsch  Maria E. Hernandez 《Aquatic Sciences - Research Across Boundaries》2013,75(1):133-149

North and Central America has a combined total of 2.5 million km² of wetlands, with 51 % in Canada, 46 % in the USA, and the remainder in subtropical and tropical Mexico and Central America. Loss rates are well known for the conterminous USA and for parts of Canada but poorly understood for Mexico and Central America. Wetlands of North America continue to be threatened due to drainage for agriculture and urban development, extreme coastal and river management, water pollution from upstream watersheds, peat mining, waterfowl management, and more recently climate change. Human use of wetlands in this region are many, including receiving ecosystem services such as water purification, flood regulation, climate regulation, and direct provisioning benefits for many cultures living in and among wetlands, especially in the Louisiana Delta and in Mexico and Central America. Climate change affects will cause wetland impacts on coastal wetlands due to sea level rise and on inland wetlands due to changes in precipitation, air temperature, and river discharges. Wetlands, in turn, have a major role in the storage of carbon in boreal regions of Canada and with carbon sequestration in temperate and tropical wetlands of the Americas.  相似文献   

A Virgo high-resolution Hα kinematical survey – II. The Atlas     

L. Chemin  C. Balkowski †  V. Cayatte †  C. Carignan †  P. Amram †  O. Garrido  O. Hernandez †  M. Marcelin †  C. Adami  A. Boselli  J. Boulesteix 《Monthly notices of the Royal Astronomical Society》2006,366(3):812-857

A catalogue of ionized gas velocity fields for a sample of 30 spiral and irregular galaxies of the Virgo cluster has been obtained by using 3D optical data. The aim of this survey is to study the influence of high-density environments on the gaseous kinematics of local cluster galaxies. Observations of the Hα line by means of Fabry–Perot interferometry have been performed at the Canada–France–Hawaii Telescope, European Southern Observatory 3.6-m telescope, Observatoire de Haute-Provence 1.93-m telescope and Observatoire du mont Mégantic telescope at angular and spectral samplings from 0.4 to 1.6 arcsec and 7 to 16 km s⁻¹. A recently developed, automatic and adaptive spatial binning technique is used to reach a nearly constant signal-to-noise ratio (S/N) over the whole field of view, allowing us to keep a high spatial resolution in high-S/N regions and extend the detection of signal in low-S/N regions. This paper is part of a series and presents the integrated emission-line and velocity maps of the galaxies. Both Hα morphologies and kinematics exhibit signs of perturbations in the form of, for example, external filaments, inner and nuclear spiral- and ring-like structures, inner kinematical twists, kinematical decoupling of a nuclear spiral, streaming motions along spiral arms and misalignment between kinematical and photometric orientation axes.  相似文献   

Chemical evolution models of local dwarf spheroidal galaxies     

Leticia Carigi  Xavier Hernandez  Gerard Gilmore 《Monthly notices of the Royal Astronomical Society》2002,334(1):117-128

We calculate chemical evolution models for four dwarf spheroidal (dSph) satellites of the Milky Way (Carina, Ursa Minor, Leo I and Leo II) for which reliable non-parametric star formation histories have been derived. In this way, the independently-obtained star formation histories are used to constrain the evolution of the systems we are treating. This allows us to obtain robust inferences on the history of such crucial parameters of galactic evolution as gas infall, gas outflows and global metallicities for these systems. We can then trace the metallicity and abundance ratios of the stars formed, the gas present at any time within the systems and the details of gas ejection, of relevance to enrichment of the galaxies environment. We find that galaxies showing one single burst of star formation (Ursa Minor and Leo II) require a dark halo slightly larger that the current estimates for their tidal radii, or the presence of a metal-rich selective wind that might carry away much of the energy output of their supernovae before this might have interacted and heated the gas content, for the gas to be retained until the observed stellar populations have formed. Systems showing extended star formation histories (Carina and Leo I), however, are consistent with the idea that their tidally-limited dark haloes provide the necessary gravitational potential wells to retain their gas. The complex time structure of the star formation in these systems remains difficult to understand. Observations of detailed abundance ratios for Ursa Minor strongly suggest that the star formation history of this galaxy might in fact resemble the complex picture presented by Carina or Leo I, but localized at a very early epoch.  相似文献   

Inland aeolian deposits of south‐west France: facies,stratigraphy and chronology     

Pascal Bertran  Mark D. Bateman  Marion Hernandez  Norbert Mercier  Dominique Millet  Luca Sitzia  Jean‐Pierre Tastet 《第四纪科学杂志》2011,26(4):374-388

Archaeological investigations undertaken along a proposed highway together with the compilation of available geological and pedological data made it possible to give a first overview of the distribution of Pleistocene aeolian deposits in south‐west France. A chronological framework for deposition has been obtained using both radiocarbon (n = 24) and luminescence (n = 26) dating. It shows that aeolian transport was very active during the Late Pleniglacial, between 15 and ～23 ka, leading to sand emplacement over a 13 000‐m² area at the centre of the basin. The Pleniglacial coversands are typified by extensive fields of small transverse to barchanoid ridges giving way to sandsheets to the east. Subsequent aeolian phases, at ca. 12 ka (Younger Dryas) and 0.8–0.2 ka (Little Ice Age), correspond to the formation of more localized and higher, mainly parabolic dunes. At the southern and eastern margins of the coversand area, aeolian dust accumulated to form loess deposits, the thickness of which reaches ～3 m on the plateaus. Luminescence dates together with interglacial‐ranking palaeoluvisols between the loess units clearly indicate that these accumulations built up during the last two glacial–interglacial cycles. The chronology of sand and loess deposition thus appears to be consistent with that already documented for northern Europe. This suggests that it was driven by global climate changes in the northern hemisphere. The relatively thin aeolian deposits (and particularly loess) in south‐west France is thought to reflect both a supply‐limited system and a moister climate than in more northern and continental regions. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

A dimensional study of disc galaxies     

X. Hernandez  B. Cervantes-Sodi 《Monthly notices of the Royal Astronomical Society》2006,368(1):351-360

We present a highly simplified model of the dynamical structure of a disc galaxy where only two parameters fully determine the solution, mass and angular momentum. We show through simple physical scalings that once the mass has been fixed, the angular momentum parameter λ is expected to regulate such critical galactic disc properties as colour, thickness of the disc and bulge-to-disc ratio. It is, hence, expected to be the determinant physical ingredient resulting in a given Hubble type. A simple analytic estimate of λ for an observed system is provided. An explicit comparison of the distribution of several galactic parameters against both Hubble type and λ is performed using observed galaxies. Both such distributions exhibit highly similar characteristics for all galactic properties studied, suggesting λ as a physically motivated classification parameter for disc galaxies.  相似文献   

Evidence for high silicic melt circulation and metasomatic events in the mantle beneath alkaline provinces: the Na–Fe-augitic green-core pyroxenes in the Tertiary alkali basalts of the Cantal massif (French Massif Central)     

S. Pilet  J. Hernandez  B. Villemant 《Mineralogy and Petrology》2002,76(1-2):39-62

Summary ?Na–Fe augitic green-core pyroxenes (hereafter called GCPX) are common in the silica-undersaturated basaltic rocks of many magmatic alkaline provinces. In the Cantal massif, green-core pyroxenes occur in nearly all the Supracantalian basalts (9.5 to 2 Ma), in contrast to the Infracantalian basalts (13 to 9.5 Ma) where they are rarely observed. An electron microprobe study demonstrates that the GCPX crystallized from evolved melts at intermediate to high pressures. Both Supra- and Infracantalian basalts show major and trace-element compositions similar to those of Ocean Island Basalts (OIB). However, the Supracantalian basalts exhibit an additional enrichment in Nb and Ta which we ascribe to a metasomatic event in the magma source. This enrichment could be related to the remobilization of metasomatic Ta and Nb-rich oxides located on grain boundaries in mantle peridotites (Bodinier et al., 1996). The hypothesis of the percolation of Si and K-rich metasomatic melts through the mantle is invoked to explain the deposition of these Ta–Nb oxides. On the basis of mineralogical and geochemical arguments, we suggest a relationship between these melts, the timing of the percolation and the formation of GCPX observed in Cantal basalts. We propose that GCPX crystallized in a melt differentiated by “percolative fractional crystallization” (PFC –Harte et al., 1993), a process which would account for the similar major-element composition of the GCPX and pyroxenes observed in the phonolites of the Cantal massif. Amphibolitic siliceous metasomatic veins in peridotite xenoliths recently described by Wulff-Pedersen et al. (1999) contain augites similar in composition to the GCPX in Cantal basalts, in addition to Nb-rich oxides. This confirms the genetic relationship between metasomatic melts, GCPX and Nb-rich oxide parageneses. GCPX would therefore seem to be linked to a metasomatic event which took place both/either during and/or between the two main stages of basaltic outpouring, and is consequently contemporaneous with the volcanism. We suggest that this process may represent a common mechanism in many alkaline provinces, where asthenospheric upwelling generates silicic metasomatizing liquids by PFC. This metasomatic process is inferred to deposit accessory phases within the lithospheric mantle, a process followed by the subsequent inheritance of this metasomatic imprint by the younger basalts. Received February 2, 2001; revised version accepted September 24, 2001  相似文献   

Distribution patterns of larval and juvenile fishes at offshore petroleum platforms in the north-central Gulf of Mexico     

David C. Lindquist  Richard F. Shaw  Frank J. Hernandez  Jr. 《Estuarine, Coastal and Shelf Science》2005,62(4):655-665

Vertical and horizontal distribution patterns of larval and juvenile fishes were described from five offshore petroleum platforms in the north-central Gulf of Mexico. Light traps and passively-fished plankton nets were used nocturnally between 1995–2000 to collect fishes in surface and deep (15–23 m depth) waters within the platform structure, and light traps were also used in surface waters directly down-current of the platforms. Light traps fished at the surface, as opposed to at-depth, collected greater CPUEs and greater diversity of larval and juvenile fishes. Of the dominant taxa collected by light traps, clupeids, engraulids, synodontids, and presettlement blenniids were most common in surface waters within the platform, while postflexion scombrids and settlement-size blenniids and pomacentrids were most common in surface waters down-current of the platforms. Deep plankton nets collected greater densities of non-clupeiform larval fishes, although surface plankton nets collected greater numbers of taxa. The vertical distribution patterns described for dominant larval fish collected by plankton nets were generally consistent with those from other studies, i.e. clupeid, carangid, sciaenid and scombrid larvae more abundant in surface waters at platforms, and synodontid, bregmacerotid, gobiid and bothid larvae more abundant in deeper waters. Oil and gas platforms likely impact larval and juvenile fish populations, particularly considering their proliferation in the Gulf (i.e., over 4000 platforms). The results from this study provide valuable baseline information for future research investigating how platforms impact the life history stages of fish populations.  相似文献   

Coastal Pollution Mitigation with Lime and Zero Valent Iron     

John L. Daniels  Gautham P. Das  Maria Teresa Serrano Hernandez  Sunyoung Bae 《Marine Georesources & Geotechnology》2006,24(3):183-191

The Taiwan Strait region has many miles of coastline, and the Taiwan Straits Tunnel (TST) project faces many potential pollution problems as construction proceeds through sensitive areas. Conventional approaches for pollution mitigation require further examination. The recent development of nanoscale particle technology has shown distinct advantages for contaminant attenuation and ground improvement. This paper is focused on trace metals and is part of the overall effort to develop the nanoscale particle technology. Trace metals in ground and surface waters represent a continued threat to human and ecological health. One of the difficulties in removing toxic concentrations of trace metals from solution is the variable oxidation state and amphoteric nature of multiple constituents. In particular, while cationic metals (e.g., Pb²⁺, Cd²⁺, Ni²⁺) may be rendered less mobile under high pH conditions, anionic metals (e.g., AsO₄^3-, CrO₄^2-, SeO₄^2-)may become more mobile. The objective of this research was to evaluate the sorption of both cationic and anionic trace elements, including arsenic (As), cadmium (Cd), chromium (Cr) and selenium (Se) under batch conditions. Mixtures of a local residual soil were tested alone and in combination with lime and zero valent iron. It was hypothesized that lime would raise the pH and precipitate positively charged metals while zero valent iron would create reducing conditions favorable to the immobilization of negatively charged metals. Results indicate that the use of lime and/or zero valent iron can increase the sorption capacity of soil. Compared to the baseline soil, sorption capacity increased with addition of lime for arsenic and cadmium while it decreased for chromium and selenium. In the case of zero valent iron addition, sorption capacity increased for cadmium, chromium and selenium, while showing no change for arsenic. When both lime and zero valent iron were used, the sorption capacity increased for all metals tested. These results suggest that the combined use of lime and zero valent iron may serve as an alternative treatment technology for removing trace metals from contaminated water systems.  相似文献   

Depleted arc volcanism in the Alboran Sea and shoshonitic volcanism in Morocco: geochemical and isotopic constraints on Neogene tectonic processes   总被引：8，自引：0，他引：8  

R.C.O. Gill  A. Aparicio  M. El Azzouzi  J. Hernandez  M.F. Thirlwall  J. Bourgois  G.F. Marriner 《Lithos》2004,78(4):363-388

Samples of volcanic rocks from Alborán Island, the Alboran Sea floor and from the Gourougou volcanic centre in northern Morocco have been analyzed for major and trace elements and Sr–Nd isotopes to test current theories on the tectonic geodynamic evolution of the Alboran Sea. The Alborán Island samples are low-K tholeiitic basaltic andesites whose depleted contents of HFS elements (0.5×N-MORB), especially Nb (0.2×N-MORB), show marked geochemical parallels with volcanics from immature intra-oceanic arcs and back-arc basins. Several of the submarine samples have similar compositions, one showing low-Ca boninite affinity. ¹⁴³Nd/¹⁴⁴Nd ratios fall in the same range as many island-arc and back-arc basin samples, whereas ⁸⁷Sr/⁸⁶Sr ratios (on leached samples) are somewhat more radiogenic. Our data point to active subduction taking place beneath the Alboran region in Miocene times, and imply the presence of an associated back-arc spreading centre. Our sea floor suite includes a few more evolved dacite and rhyolite samples with (⁸⁷Sr/⁸⁶Sr)₀ up to 0.717 that probably represent varying degrees of crustal melting. The shoshonite and high-K basaltic andesite lavas from Gourougou have comparable normalized incompatible-element enrichment diagrams and Ce/Y ratios to shoshonitic volcanics from oceanic island arcs, though they have less pronounced Nb deficits. They are much less LIL- and LREE-enriched than continental arc analogues and post-collisional shoshonites from Tibet. The magmas probably originated by melting in subcontinental lithospheric mantle that had experienced negligible subduction input. Sr–Nd isotope compositions point to significant crustal contamination which appears to account for the small Nb anomalies.

The unmistakable supra-subduction zone (SSZ) signature shown by our Alboran basalts and basaltic andesite samples refutes geodynamic models that attribute all Neogene volcanism in the Alboran domain to decompression melting of upwelling asthenosphere arising from convective thinning of over-thickened lithosphere. Our data support recent models in which subsidence is caused by westward rollback of an eastward-dipping subduction zone beneath the westernmost Mediterranean. Moreover, severance of the lithosphere at the edges of the rolling-back slab provides opportunities for locally melting lithospheric mantle, providing a possible explanation for the shoshonitic volcanism seen in northern Morocco and more sporadically in SE Spain.  相似文献   

Characterizing the vadose zone and a perched aquifer near the Vosges ridge at the La Soutte experimental site,Obernai, France     

Pascal Sailhac  Maksim Bano  Mickael Behaegel  Jean-François Girard  Ester Falgàs Para  Juanjo Ledo  Guy Marquis  Pierre-Daniel Matthey  José Ortega-Ramírez 《Comptes Rendus Geoscience》2009,341(10-11):818-830

We consider a series of hydrogeophysical techniques that provide a multiscale investigation of the water content in the vadose zone and of the perched aquifer at the experimental site of “La Soutte” in the Vosges Mountains (France). It is located in a catchment area where several springs and streams occur along fractured volcanic and weathered plutonic rocks. The site is the object of a long-term study that uses both continuous and repeated measurements to monitor hydrogeological processes. The main results from AMT and DC resistivity techniques allow the determination of a high-resolution 3D resistivity model over a large range of depths (from 10⁰ to 10³ m). We discuss their use and propose a hydrogeological model (porosity, water conductivity and water content). We also use MRS and GPR for a detailed investigation of the shallow part of the catchment that consists of soil and weathered rocks of highly varying thickness (0 to 15 m). MRS is used to map the thickness and total water volume content by unit surface of the saturated weathered zone. It also yields estimates of the vadose zone thickness through the depth to the top of the saturated zone. Moreover, we show results from GPR CMP measurements that yield estimates of the water content and porosity in the shallowest layer (0–30 cm) by simple interpretation of the ground direct wave.  相似文献