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Changes in the species composition and structure of Mediterranean macroalgal-dominated communities from the upper sublittoral zone are described along a gradient of nutrient enrichment coming from a urban sewage outfall. Ulva-dominated communities only appear close to the sewage outfall. Corallina-dominated communities replace ulvacean algae at intermediate levels of nutrient enrichment. Cystoseira-dominated communities thrive in the reference site but already appear at nutrient levels that are threefold higher than those reported from unpolluted sites. Assemblage variability of Cystoseira-dominated communities decreases along the gradient of nutrient enrichment. Methods based on the functional-form groups of macroalgae to assess the water quality provide equivocal results at intermediate levels of nutrient enrichment because species belonging to the same group can display a completely different response to pollution. Alternatively, methods based on indicator species showed correlated evidence among species abundances and pollution levels and seem to have better performances in water quality assessment. 相似文献
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Sonia Jerez Juan Pedro Montavez Juan Jose Gomez-Navarro Raquel Lorente-Plazas Juan Andres Garcia-Valero Pedro Jimenez-Guerrero 《Climate Dynamics》2013,41(7-8):1749-1768
This study illustrates the sensitivity of regional climate change projections to the model physics. A single-model (MM5) multi-physics ensemble of regional climate simulations over the Iberian Peninsula for present (1970–1999) and future (2070–2099 under the A2 scenario) periods is assessed. The ensemble comprises eight members resulting from the combination of two options of parameterization schemes for the planetary boundary layer, cumulus and microphysics. All the considered combinations were previously evaluated by comparing hindcasted simulations to observations, none of them providing clearly outlying climates. Thus, the differences among the various ensemble members (spread) in the future projections could be considered as a matter of uncertainty in the change signals (as similarly assumed in multi-model studies). The results highlight the great dependence of the spread on the synoptic conditions driving the regional model. In particular, the spread generally amplifies under the future scenario leading to a large spread accompanying the mean change signals, as large as the magnitude of the mean projected changes and analogous to the spread obtained in multi-model ensembles. Moreover, the sign of the projected change varies depending on the choice of the model physics in many cases. This, together with the fact that the key mechanisms identified for the simulation of the climatology of a given period (either present or future) and those introducing the largest spread in the projected changes differ significantly, make further claims for efforts to better understand and model the parameterized subgrid processes. 相似文献
45.
Chemical availability of arsenic and heavy metals in sediments from abandoned cinnabar mine tailings 总被引：1，自引：1，他引：0
Raquel Larios Rodolfo Fernández-Martínez Verónica Silva Isabel Rucandio 《Environmental Earth Sciences》2013,68(2):535-546
The understanding of the solid-phase speciation of arsenic in soils and sediments is important in the evaluations of its potential mobility and availability in the environment. The spoil heaps of abandoned mercury mines contain waste materials with high arsenic and heavy metals concentrations. The weathering of these tailings can cause their mobilization to the surroundings. In this work, the mobility and availability of arsenic and some heavy metals were evaluated in sediments from two heavily polluted mercury mining districts in Asturias (NW Spain). For this purpose, a slightly modified version of the Bureau Community of Reference sequential extraction scheme was applied to sediments. The total contents in the operationally defined fractions were analysed by inductively coupled plasma-atomic emission spectrometry. Extremely high total arsenic concentrations were found in all sediments ranging from 4,000 to 24,800 mg kg?1. High easily mobilizable arsenic contents were found in the first mining area, related to the solubilization of Ca-bearing phases, supported by extracts analyses, X-ray diffraction results and the positive correlation found among the As and Ca fractionations. Ni and Zn were the most mobile among heavy metals, being Cr the least mobile, suggesting an anthropogenic origin due to the metallurgical processes, transport or dispersion generated from neighbour spoil heaps. In the second mining area, the bulk of As was concentrated in the residual phase, as well as Cr, Cu, Fe, Pb, Ti, indicating a mineralogical origin and the low availability of these elements. The strong correlations established between As and Fe and Ti distributions support the hypothesis that As is mainly associated to structural mineral phases in these sediments. 相似文献
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Manuel Frochoso Raquel González-Pellejero Fernando Allende 《Central European Journal of Geosciences》2013,5(1):12-27
The timing of the local last glacial maximum in the mountains of the Northern Iberian Peninsula is not synchronous with the global Last Glacial Maximum (LGM) probably due to the marginal position of the Northern Iberian Peninsula within the European continent. The study of a Cantabrian massif, the Asón platform and summits, provides new data on the extent and timing of the local last glaciation. Here we can place the last maximal extent of glaciers during Early Würm, according to OSL dating on till samples. The main glaciers developed at least between 78-65 ka BP, well centred on MIS 4 and even the transition to MIS 5. The erosive efficacy of these glaciers decreased later, ca. 45–40 ka BP, until they abruptly disappeared from the edges of the massif. A new ice advance left well-defined moraines at the edges of the massif’s internal depressions, indicating a tongue disjunction phase with two glacier sub-stages, probably one at the beginning of the cooling ca. 27–25 ka BP, followed by a retreat and another glacial advance ca. 21–18 ka BP. After these episodes the glaciers disappeared from the Asón Mountains and only some residual glaciers were formed that may be related to the LGM. 相似文献
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Abstract– The rock record from the early solar system indicates high‐temperature thermal processing sufficient to melt refractory oxides and silicates. The astrophysical context for the formation and evolution of our solar system, from a molecular cloud to a “clean” planetary system, is difficult to constrain tightly because of the large scales and lack of resolution of astronomical observations. Protostellar jets and winds, commonly associated with forming stars, are likely to play a role in heating and redistribution of the processed material in the solar system. We have recently proposed that disk‐winds can cause melting of small inclusions to distances out to several AU. Particularly energetic outbursts, such as the FU‐Orionis and EXor events, occur over relatively short time scales (approximately 100 and 1 yr, respectively), and are probably events related to formation of the refractory solids present in primitive meteorites. 相似文献
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Mauricio da Rocha Fragoso Gabriel Vieira de Carvalho Felipe Lobo Mendes Soares Daiane Gracieli Faller Luiz Paulo de Freitas Assad Raquel Toste Lívia Maria Barbosa Sancho Elisa Nóbrega Passos Carina Stefoni Böck Bruna Reis Luiz Landau Hernan G. Arango Andrew M. Moore 《Ocean Dynamics》2016,66(3):419-434
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Florian Neumann Alberto Vásquez-Serrano Gustavo Tolson Raquel Negrete-Aranda Juan Contreras 《Pure and Applied Geophysics》2016,173(10-11):3395-3417
50.