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1.
Diopatra neapolitana Delle Chiaje, 1841 (Annelida, Onuphidae) is an important economic natural resource in Ria de Aveiro (northwestern coast of Portugal) and throughout Europe. The species is intensively harvested for use as fresh bait. However, there is only limited knowledge about its life cycle derived from a previous study in Mediterranean Sea. Reproduction and development patterns are known to vary biogeographically, making it important to base management decisions on locally appropriate information. This work examines reproduction patterns for populations from the Eastern Atlantic, which have not previously been assessed, with an eye towards drawing Atlantic–Mediterranean comparisons and informing local management strategies. The study was conducted from May 2007 to April 2009 in Ria de Aveiro. The reproductive biology of D. neapolitana was described from the proportional variation of worms with gametes in the coelom and from the progression of the oocyte diameter. Individuals with gametes inside the coelom were found all year round, but the peak reproductive period occurred between May and August, when almost all individuals had gametes in the coelom and females contained more oocytes than at any other time of the year. The overall male:female ratio was close to 1:1 and the oocyte diameter ranged from 40 to 240 μm. In vitro fertilization was performed and the results compared to other studies. Based on the present results, some protection measures are suggested to implement a sustainable exploitation of the species. 相似文献
2.
Long-term considerations of repeated and increasing sand extraction on the Netherlands Continental Shelf (North Sea) may lead to the creation of a mega-scale extraction trench in front of the Dutch coast (length hundreds of km, width over 10 km, depth several m). We investigate the impact of such a huge topographic intervention on tidal dynamics, which is a key aspect in hydrodynamics, and indirectly also affecting morphodynamics and ecology. 相似文献
3.
Patrick Materatski Anna-Maria Vafeiadou Tom Moens Helena Adão 《Estuaries and Coasts》2016,39(5):1478-1490
In 2008, the stable seagrass beds of the Mira estuary (SW Portugal) disappeared completely; however, during 2009, they have begun to present early symptoms of natural recovery, characterised by a strongly heterogeneous distribution. This study was designed to investigate the spatial and temporal variability patterns of species composition, densities and trophic composition of the benthic nematode assemblages in this early recovery process, at two sampling sites with three stations each and at five sampling occasions. Because of the erratic and highly patchy seagrass recovery and the high environmental similarity of the two sampling sites, we expected within-site variability in nematode assemblages to exceed between-site variability. However, contrary to that expectation, whilst nematode genus composition was broadly similar between sites, nematode densities differed significantly between sites, and this between-site variability exceeded within-site variability. This may be linked to differences in the Zostera recovery patterns between both sites. In addition, no clear temporal patterns of nematode density, trophic composition and diversity were evident. Nematode assemblages generally resembled those of other estuarine muddy intertidal areas, which have a high tolerance of stress conditions. 相似文献
4.
Nadia Senechal Stéphane Abadie Edith Gallagher Jamie MacMahan Gerd Masselink Hervé Michallet Ad Reniers Gerben Ruessink Paul Russell Damien Sous Ian Turner Fabrice Ardhuin Philippe Bonneton Stéphane Bujan Sylvain Capo Raphael Certain Rodrigo Pedreros Thierry Garlan 《Ocean Dynamics》2011,61(12):2073-2098
A large multi-institutional nearshore field experiment was conducted at Truc Vert, on the Atlantic coast of France in early 2008. Truc Vert’08 was designed to measure beach change on a long, sandy stretch of coast without engineering works with emphasis on large winter waves (offshore significant wave height up to 8 m), a three-dimensional morphology, and macro-tidal conditions. Nearshore wave transformation, circulation and bathymetric changes involve coupled processes at many spatial and temporal scales thus implying the need to improve our knowledge for the full spectrum of scales to achieve a comprehensive view of the natural system. This experiment is unique when compared with existing experiments because of the simultaneous investigation of processes at different scales, both spatially (from ripples to sand banks) and temporally (from single swash events to several spring-neap tidal cycles, including a major storm event). The purpose of this paper is to provide background information on the experiment by providing detailed presentation of the instrument layout and snapshots of preliminary results. 相似文献
5.
Prey diversity of Homo sapiens in north Iberia exhibited shifts associated with climate warming after the Last Glacial Maximum, as deduced from animal remains obtained from Upper Palaeolithic caves in Asturias (northern Spain). Significant association of prey diversity and river proximity was found during adverse climate conditions, indicating opportunistic predation. A high increase of prey diversity was found when small animals (including fish) were taken into account in archaeological records, highlighting the importance of this type of prey in Palaeolithic diets. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
6.
L. Ferrer A. Fontán J. Mader G. Chust M. González V. Valencia Ad. Uriarte M.B. Collins 《Continental Shelf Research》2009,29(8):970-984
Low-salinity waters, within the upper layers of the water column, have been observed in the oceanic region of the southeastern limit of the Bay of Biscay (in March, 2007). This contribution assesses the potential role of large surface freshwater discharges from the Adour (France), Nervión, Oria, Deba, Urola, Urumea and Bidasoa (Basque Country) rivers, to explain the presence of these low-salinity waters. Such discharges, within the offshore waters, reached to at least 50 m in depth; likewise, extending over 15–20 km, in the horizontal. This pattern is confirmed by field data collected by offshore buoys, model results, and the analysis of satellite images. The presence of the low-salinity waters is corroborated by numerical simulations, performed by the ROMS (Regional Ocean Modeling System) hydrodynamic model, with the incorporation of river discharges. In order to simulate the freshwater movements and to identify their origin, particles were released at the river mouths and dispersed (by a Lagrangian particle-tracking model, LPTM), supplied by 3-hourly current fields derived from the ROMS model. The plumes of the Nervión, Oria, Urola and Urumea rivers appear to be the main factors contributing to the low-salinity field, at the offshore locations of the buoys. This pattern is related mainly to the prevailing oceano-meteorological conditions, over the period of analysis. 相似文献
7.
The electrical conductivity of Posidonia black shales — from magnetotelluric exploration to rock samples 下载免费PDF全文
We carried out a magnetotelluric field campaign in the South–East Lower Saxony Basin, Germany, with the main goal of testing this method for imaging regional Posidonia black shale sediments. Two‐dimensional inversion results of the magnetotelluric data show a series of conductive structures correlating with brine‐saturated sediments but also with deeper, anthracitic Westphalian/Namurian coals. None of these structures can be directly related with the Posidonia black shale, which appears to be generally resistive and therefore difficult to resolve with the magnetotelluric method. This assumption is supported by measurements of electrical resistivity on a set of Posidonia shale samples from the Hils syncline in the Lower Saxony basin. These rock samples were collected in shallow boreholes and show immature (0.53% Ro), oil (0.88% Ro), and gas (1.45% Ro) window thermal maturities. None of the black shale samples showed low electrical resistivity, particularly those with oil window maturity show resistivity exceeding 104 Ωm. Moreover, we could not observe a direct correlation between maturity and electrical resistivity; the Harderode samples showed the highest resistivity, whereas the Haddessen samples showed the lowest. A similar trend has been seen for coals in different states of thermal maturation. Saturation of the samples with distilled and saline water solutions led to decreasing electrical resistivity. Moreover, a positive correlation of electrical resistivity with porosity is observed for the Wickensen and Harderode samples, which suggests that the electrical resistivity of the Posidonia black shale is mainly controlled by porosity. 相似文献
8.
Adão H. Matonse Donald C. Pierson Allan Frei Mark S. Zion Aavudai Anandhi Elliot Schneiderman Ben Wright 《Climatic change》2013,116(3-4):437-456
Future climate scenarios projected by three different General Circulation Models and a delta-change methodology are used as input to the Generalized Watershed Loading Functions – Variable Source Area (GWLF-VSA) watershed model to simulate future inflows to reservoirs that are part of the New York City water supply system (NYCWSS). These inflows are in turn used as part of the NYC OASIS model designed to simulate operations for the NYCWSS. In this study future demands and operation rules are assumed stationary and future climate variability is based on historical data to which change factors were applied in order to develop the future scenarios. Our results for the West of Hudson portion of the NYCWSS suggest that future climate change will impact regional hydrology on a seasonal basis. The combined effect of projected increases in winter air temperatures, increased winter rain, and earlier snowmelt results in more runoff occurring during winter and slightly less runoff in early spring, increased spring and summer evapotranspiration, and reduction in number of days the system is under drought conditions. At subsystem level reservoir storages, water releases and spills appear to be higher and less variable during the winter months and are slightly reduced during summer. Under the projected future climate and assumptions in this study the NYC reservoir system continues to show high resilience, high annual reliability and relatively low vulnerability. 相似文献
9.
Dissolved and suspended concentrations of hexachlorocyclohexane isomers, α, γ and δ HCH, and Zn, Cu and Cd have been measured in the Napostá Grande stream, located in the Blance Bay area, Argentina, for the purpose of studying the behaviour of these compounds in the freshwater-seawater mixing zone. The aim was to establish the mobilization processes, according to their distribution over the dissolved and suspended forms, in order to obtain a better understanding of their impact on organochlorine and heavy metal levels in the marine environment. It is concluded that the compounds studied are removed from solution by suspended matter which is afterwards precipitated during the freshwater-seawater mixing process. Seawater and surface sediment concentrations of these pollutants for two sampling sites in Blanca Bay, Argentina, are also reported. 相似文献
10.
Adélie Delacour Marie-Christine Gerbe Jean-Claude Thouret Gerhard Wörner Perrine Paquereau-Lebti 《Bulletin of Volcanology》2007,69(6):581-608
Minor centres in the Central Volcanic Zone (CVZ) of the Andes occur in different places and are essential indicators of magmatic
processes leading to formation of composite volcano. The Andahua–Orcopampa and Huambo monogenetic fields are located in a
unique tectonic setting, in and along the margins of a deep valley. This valley, oblique to the NW–SE-trend of the CVZ, is
located between two composite volcanoes (Nevado Coropuna to the east and Nevado Sabancaya to the west). Structural analysis
of these volcanic fields, based on SPOT satellite images, indicates four main groups of faults. These faults may have controlled
magma ascent and the distribution of most centres in this deep valley shaped by en-echelon faulting. Morphometric criteria
and 14C age dating attest to four main periods of activity: Late Pleistocene, Early to Middle Holocene, Late Holocene and Historic.
The two most interesting features of the cones are the wide compositional range of their lavas (52.1 to 68.1 wt.% SiO2) and the unusual occurrence of mafic lavas (olivine-rich basaltic andesites and basaltic andesites). Occurrence of such minor
volcanic centres and mafic magmas in the CVZ may provide clues about the magma source in southern Peru. Such information is
otherwise difficult to obtain because lavas produced by composite volcanoes are affected by shallow processes that strongly
mask source signatures. Major, trace, and rare earth elements, as well as Sr-, Nd-, Pb- and O-isotope data obtained on high-K
calc-alkaline lavas of the Andahua–Orcopampa and Huambo volcanic province characterise their source and their evolution. These
lavas display a range comparable to those of the CVZ composite volcanoes for radiogenic and stable isotopes (87Sr/86Sr: 0.70591–0.70694, 143Nd/144Nd: 0.512317–0.512509, 206Pb/204Pb: 18.30–18.63, 207Pb/204Pb: 15.57–15.60, 208Pb/204Pb: 38.49–38.64, and δ
18O: 7.1–10.0‰ SMOW), attesting to involvement of a crustal component. Sediment is absent from the Peru–Chile trench, and hence
cannot be the source of such enrichment. Partial melts of the lowermost part of the thick Andean continental crust with a
granulitic garnet-bearing residue added to mantle-derived arc magmas in a high-pressure MASH [melting, assimilation, storage
and homogenisation] zone may play a major role in magma genesis. This may also explain the chemical characteristics of the
Andahua–Orcopampa and Huambo magmas. Fractional crystallisation processes are the main governors of magma evolution for the
Andahua–Orcopampa and Huambo volcanic province. An open-system evolution is, however, required to explain some O-isotopes
and some major and trace elements values. Modelling of AFC processes suggests the Charcani gneisses and the local Andahua–Orcopampa
and Huambo basement may be plausible contaminants. 相似文献