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51.
C. Vinagre A. Maia P. Reis-Santos M.J. Costa H.N. Cabral 《Estuarine, Coastal and Shelf Science》2009,81(3):296-300
The distribution of Solea solea and Solea senegalensis in the Tagus estuary was studied following a small-scale approach. Preliminary sampling revealed that sole concentrated in two areas within their nursery grounds, the main subtidal channel and a large intertidal mudflat. Beam trawls were conducted intensively in the two areas in July 2006. Depth, salinity and water temperature were measured. Substrate samples were collected for sediment type determination and macrobenthos identification and quantification. Generalized linear models were applied in order to explain the occurrence and variability of soles' densities, using depth, salinity, water temperature and abundance of polychaetes, oligochaetes, amphipods, isopods and bivalves as explanatory variables. While S. solea was more abundant in the main subtidal channel, a deeper, warmer and lower salinity area, S. senegalensis abundance was highest at the intertidal mudflat area. Presence of both species in the two areas was associated with abundance of polychaetes (generally with another variable associated), and for S. senegalensis in the subtidal channel it was associated with amphipods and depth. Abundance of S. solea in the main subtidal channel was associated mainly with polychaetes abundance, while that of S. senegalensis was associated with amphipods density. In the intertidal mudflat, bivalves and polychaetes presented significant relationships with both species densities. Some of the factors that had been reported to be important for the distribution of these species in previous studies also do so at a finer scale; however, this small-scale approach provided an in-depth knowledge on habitat selection and spatial segregation of these species within this nursery area. 相似文献
52.
Concurrent imaging of chlorophyll fluorescence,Chlorophyll a content and green fluorescent proteins‐like proteins of symbiotic cnidarians 下载免费PDF全文
Miguel Costa Leal Bruno Jesus João Ezequiel Ricardo Calado Rui Jorge Miranda Rocha Paulo Cartaxana João Serôdio 《Marine Ecology》2015,36(3):572-584
Research on photosynthetic cnidarians has been mainly focused on the symbiosis established between the cnidarian host and its dinoflagellates endosymbionts from genus Symbiodinium. Despite the potential of imaging techniques for assessing the spatial distribution of key parameters of cnidarian photobiology, such as photochemical activity, chlorophyll a content or green fluorescent proteins (GFPs), to our best knowledge, no study has ever attempted to simultaneous map these three features. In this study, we developed a modified imaging pulse amplitude fluorometer by applying excitation light of different wavelengths and selectively detecting short spectral bands through bandpass filters. The imaging system was used to sequentially excite and quantify chlorophyll variable fluorescence (maximum quantum yield of photosystem II, Fv/Fm), Chl a content (normalized difference vegetation index) and relative content of GFPs. The spatial distribution of these photophysiological parameters was mapped both horizontally, across the surface of the soft corals Sarcophyton cf. glaucum and Sinularia flexibilis and the zoanthid Protopalythoa sp., and vertically, throughout a vertical section of S. cf. glaucum. Results showed bleached areas within each individual coral colony and registered photophysiological changes with S. cf. glaucum tissue depth. Analysis of Protopalythoa sp. polyps’ expansion revealed differential surface patterns of NDVI and GFP concentration, and a negative relation between these latter parameters within each polyp. This novel non‐invasive approach allowed a high‐resolution characterization of the spatial relationship between these key parameters through the analysis of image information on a pixel‐by‐pixel basis, which has great potential for investigating the physiological state of symbiotic associations. 相似文献
53.
54.
Bengt Gustafsson Jorge Meléndez Martin Asplund David Yong 《Astrophysics and Space Science》2010,328(1-2):185-191
The question whether the solar chemical composition is typical for solar-type stars is analysed by comparing the Sun with different stellar samples, including a sample of stars with very similar parameters, solar twins. Although typical in terms of overall metallicity for stars of solar age and galactic orbit, the solar atmosphere is found to have abundances, as compared with solar twins, that indicate that its gas has once been affected by dust formation and dust separation. It is concluded that this may be related to the formation of the solar planetary system and its special properties. 相似文献
55.
Limaverde AM Wagener Ade L Fernandez MA Scofield Ade L Coutinho R 《Marine environmental research》2007,64(3):384-398
Stramonita haemastoma was investigated as a suitable bioindicator of TBT and TPhT contamination in the tropical Atlantic Ocean by: 1. Imposex induction in healthy females after inoculation with TBT and TPhT in the laboratory; and 2. Determining incidence of imposex in S. haemastoma collected from areas with various levels of tributyltin (TBT) and triphenyltin (TPhT) and determining the concentrations of these chemical in its tissues and that of its prey, the mussell Perna pernas. Imposex intensities and organotin concentrations in tissues showed good correlation, indicating S. haemastoma as a reliable bioindicator of TBT and TPhT contamination in coastal waters. Body burden threshold of TBT and TPhT for imposex induction was estimated to be 10-20 ng g(-1). 相似文献
56.
The Mississippi Valley-type (MVT) Pb–Zn ore district at Mežica is hosted by Middle to Upper Triassic platform carbonate rocks
in the Northern Karavanke/Drau Range geotectonic units of the Eastern Alps, northeastern Slovenia. The mineralization at Mežica
covers an area of 64 km2 with more than 350 orebodies and numerous galena and sphalerite occurrences, which formed epigenetically, both conformable
and discordant to bedding. While knowledge on the style of mineralization has grown considerably, the origin of discordant
mineralization is still debated. Sulfur stable isotope analyses of 149 sulfide samples from the different types of orebodies
provide new insights on the genesis of these mineralizations and their relationship. Over the whole mining district, sphalerite
and galena have δ
34
S values in the range of –24.7 to –1.5‰ VCDT (–13.5 ± 5.0‰) and –24.7 to –1.4‰ (–10.7 ± 5.9‰), respectively. These values are
in the range of the main MVT deposits of the Drau Range. All sulfide δ
34
S values are negative within a broad range, with δ
34
S
pyrite <δ
34
S
sphalerite <δ
34
S
galena for both conformable and discordant orebodies, indicating isotopically heterogeneous H2S in the ore-forming fluids and precipitation of the sulfides at thermodynamic disequilibrium. This clearly supports that
the main sulfide sulfur originates from bacterially mediated reduction (BSR) of Middle to Upper Triassic seawater sulfate
or evaporite sulfate. Thermochemical sulfate reduction (TSR) by organic compounds contributed a minor amount of 34S-enriched H2S to the ore fluid. The variations of δ
34
S values of galena and coarse-grained sphalerite at orefield scale are generally larger than the differences observed in single
hand specimens. The progressively more negative δ
34
S values with time along the different sphalerite generations are consistent with mixing of different H2S sources, with a decreasing contribution of H2S from regional TSR, and an increase from a local H2S reservoir produced by BSR (i.e., sedimentary biogenic pyrite, organo-sulfur compounds). Galena in discordant ore (–11.9
to –1.7‰; –7.0 ± 2.7‰, n = 12) tends to be depleted in 34
S compared with conformable ore (–24.7 to –2.8‰, –11.7 ± 6.2‰, n = 39). A similar trend is observed from fine-crystalline sphalerite I to coarse open-space filling sphalerite II. Some variation
of the sulfide δ
34
S values is attributed to the inherent variability of bacterial sulfate reduction, including metabolic recycling in a locally
partially closed system and contribution of H2S from hydrolysis of biogenic pyrite and thermal cracking of organo-sulfur compounds. The results suggest that the conformable
orebodies originated by mixing of hydrothermal saline metal-rich fluid with H2S-rich pore waters during late burial diagenesis, while the discordant orebodies formed by mobilization of the earlier conformable
mineralization. 相似文献
57.
Groundwater recharge in irrigated semi-arid areas: quantitative hydrological modelling and sensitivity analysis 总被引:3,自引:0,他引:3
Joaquín Jiménez-Martínez Lucila Candela Jorge Molinero Karim Tamoh 《Hydrogeology Journal》2010,18(8):1811-1824
For semi-arid regions, methods of assessing aquifer recharge usually consider the potential evapotranspiration. Actual evapotranspiration rates can be below potential rates for long periods of time, even in irrigated systems. Accurate estimations of aquifer recharge in semi-arid areas under irrigated agriculture are essential for sustainable water-resources management. A method to estimate aquifer recharge from irrigated farmland has been tested. The water-balance-modelling approach was based on VisualBALAN v. 2.0, a computer code that simulates water balance in the soil, vadose zone and aquifer. The study was carried out in the Campo de Cartagena (SE Spain) in the period 1999–2008 for three different groups of crops: annual row crops (lettuce and melon), perennial vegetables (artichoke) and fruit trees (citrus). Computed mean-annual-recharge values (from irrigation+precipitation) during the study period were 397 mm for annual row crops, 201 mm for perennial vegetables and 194 mm for fruit trees: 31.4, 20.7 and 20.5% of the total applied water, respectively. The effects of rainfall events on the final recharge were clearly observed, due to the continuously high water content in soil which facilitated the infiltration process. A sensitivity analysis to assess the reliability and uncertainty of recharge estimations was carried out. 相似文献
58.
Numerous approaches exist for the prediction of the settlement improvement offered by the vibro-replacement technique in weak or marginal soil deposits. The majority of the settlement prediction methods are based on the unit cell assumption, with a small number based on plane strain or homogenisation techniques. In this paper, a comprehensive review and assessment of the more popular settlement prediction methods is carried out with a view to establishing which method(s) is/are in best agreement with finite element predictions from a series of PLAXIS 2D axisymmetric analyses on an end-bearing column. The Hardening Soil Model in PLAXIS 2D has been used to model the behaviour of both the granular column material and the treated soft clay soil. This study has shown that purely elastic settlement prediction methods overestimate the settlement improvement for large modular ratios, while the methods based on elastic–plastic theory are in better agreement with finite element predictions at higher modular ratios. In addition, a parameter sensitivity study has been carried out to establish the influence of a range of different design parameters on predictions obtained using a selection of elastic–plastic methods. 相似文献
59.
Letícia Fleck Fadel Miguel Jorge Daniel Riera Ignacio Iturrioz 《国际地质力学数值与分析法杂志》2008,32(15):1857-1881
The numerical fracture analysis of non‐homogeneous rock or concrete dowels subjected to shear and compression is described in detail. The method of analysis allows the consideration of scale and rate effects due to material non‐homogeneity and fracture. The proposed approach is verified by comparing numerical predictions with experimental results reported in the literature for a series of small rock samples, since experimental evidence for large bodies is not yet available (2007). Results generated by Monte Carlo simulation using the so‐called discrete element method to model the dowels suggest that a simple three parameters law can be used to predict the relationship between tangential stress at the base and lateral distortion. It is observed that the larger the size of the cubes, the smaller both the peak tangential stress and the rupture distortion. Size effects are also evaluated in samples with vertical restraint. The influence of loading rate is likewise numerically assessed for two sample sizes. The effect is compatible with experimental evidence available for concrete using small samples. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
60.
Filipe Rafael Ceia Joana Patrício João Carlos Marques João Alveirinho Dias 《Ocean & Coastal Management》2010,53(8):478-486
Coastal vulnerability in barrier island systems is extremely high. The barrier island shoreline is exposed to many threats, such as storm erosion, reductions in sediment longshore drift and sea level rise. Many of these threats to coastal areas, such as Ria Formosa, are likely to increase in the near future. The main objectives of the present study are to identify the areas in the system that are at most risk by assessing the evolution of the Ria Formosa barrier island system since the 1940s, and determine which interventions would be necessary to protect these areas.The coastal vulnerability of the system was assessed based on current literature, data available from official institutions, and aerial and terrestrial in situ examination. The results obtained for the evolution of the Ria Formosa coastal system reveal that there are several vulnerable areas that have very dynamic processes, such as extremely high evolution rates of islands and inlets. Human actions that affect the whole system, namely the construction of many physical structures, are the main cause of the instability. Moreover, as several stakeholders are involved, efficient management of the coastal system is imperative. Extensive and careful interventions are urgently needed to avoid irreversible negative impacts on the barrier island system. Three types of techniques could be adopted to deal with the threats to barrier islands: hard stabilization, soft techniques, and non-structural alternatives. However, using hard techniques has many negative effects compared to soft techniques, and as a result it is necessary to remove existing structures from the areas at most risk. 相似文献