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151.
Abstract. The Lago di Varano is situated on the north side of the Gargano National Park (southeast Italy) and covers a surface area of about 65 km2. It communicates with the Adriatic Sea through two artificial canals (Foce Capoiale and Foce Varano) located at the two ends of a long and narrow coastal dune. This work presents preliminary results of four seasonal surveys (1999–2000) carried out to measure chemical and physical parameters of the water column (temperature, salinity, dissolved oxygen and pH) and to analyse a number of biogeochemical characteristics of surface sediments (organic matter, total phosphorus, total nitrogen and total Hg, As, Pb, Cd, Cr, Cu and Ni content). Water analysis indicated poor exchange between the coastal pond and the open sea, limited to autumn and winter. Surface sediments were rich in organic matter, whose distribution was influenced by chemical-physical and hydrodynamic variations in the water column. At the sediment level, the highest values of Cd were found in the central zone of the basin, while the highest Cr values were measured in the central and southeastern areas. With the exception of Cd and Pb, the metal content did not indicate anthropogenic pollution, in particular when compared with the Venice Lagoon and the Central Adriatic Sea.  相似文献   
152.
In this project we investigated the ecotoxicological effects of endocrine disrupters in a four-year survey of the Mediterranean population of swordfish (Xiphias gladius). In the Mediterranean environment, top predators, such as swordfish, accumulate high concentrations of polyhalogenated aromatic hydrocarbons (PHAHs) and toxic metals, potentially incurring high toxicological risk. The effects of organochlorines and trace elements (Hg, Cd and Pb) in 192 swordfish specimens, caught in the Strait of Messina, Sicily, Italy, were investigated using vitellogenin (Vtg), zona radiata proteins (Zrp) and CYP1A (BPMO, EROD) activities. Vtg and Zrp were found to be dramatically induced in some adult male specimens, suggesting that this species is highly exposed to estrogens in the Mediterranean Sea. A role of organochlorines in this induction phenomenon is suggested by the statistically significant correlations between Zrp in plasma and PCB concentrations in muscle (p<0.032) and Vtg in plasma and PCB concentrations in liver (p<0.034) of male specimens. Levels of trace elements in liver were in the following ranges: Hg 1–22, Cd 1–28 and Pb 0–1.6 ppm d.w. These data indicate potential reproductive alterations in large pelagic fish and suggest the need for continuous monitoring to avoid reductions in the population of this fish species of high commercial and ecological interest.  相似文献   
153.
Abstract

Helical piles are used mainly to resist tension forces generated by uplift and overturning moments of various structures, therefore they have been suggested as a potential alternative to driven piles as offshore pile because they provide a large uplift capacity due to the anchor effect of the helix. To date no standards are available for the assessment of the use of helical piles in the offshore environment. State-of-the art installation and uplift capacity assessment is based on field onshore tests on small helical piles. The purpose of this review is to critically evaluate the current knowledge on helical piles considering uplift capacity, cyclic load, installation torque models and the parameters affecting the installation torque, to understand whether they can be considered for potential offshore applications. The paper could be of valuable interest for engineers and contractors involved in the offshore installation of piles.  相似文献   
154.
Debris‐covered glaciers may host several biological forms that colonize the debris cover, especially if the glacier tongue reaches sufficiently low altitudes (down to about 1700 m a.s.l. at Miage Glacier, Western Italian Alps) thus allowing also tree growth. Supraglacial trees colonizing the debris‐covered tongue are strongly influenced in growth and distribution by substrate characteristics and instability. The tree age distribution at Miage Glacier presents a positive gradient towards the glacier terminus, which was found to be related to the decreasing glacier surface velocity. By analysing tree‐ring growth anomalies on the glacier and at a control site at the tree line over the 20‐year period 1987–2006, it was found that trees growing on the glacier presented the highest percentages of abrupt growth changes (AGCs)>+70% with respect to the four previous years. Considering tree displacement on the glacier surface over the same 20‐year period and the recorded AGCs, it was found that the central‐lower portion of the southern lobe towards the margins was the most unstable. The temporal analysis of AGC>+40% confirmed a period of higher glacier surface instability, reaching a maximum in the years 1988 (on lobe S) and 1989 (on lobe N), probably related to the passage of a kinematic wave in the glacier tongue. Our analysis suggests that supraglacial trees hold useful information on the glacier tongue dynamics and that both AGC>+70% and AGC>+40% may be used as a proxy for substrate instability in spatio‐temporal reconstructions in the Alpine environment.  相似文献   
155.
A multi‐proxy record is presented for approximately the last 4500 cal a BP from Lake Shkodra, Albania/Montenegro. Lithological analyses, C/N ratio and δ13C of the organic and inorganic carbon component suggest that organic matter and bulk carbonate are predominantly authigenic. The δ18O record of bulk carbonate indicates the presence of two prominent wet periods: one at ca. 4300 cal a BP and one at ca. 2500–2000 cal a BP. The latter phase is also found in southern Spain and Central Italy, and represents a prominent event in the western and central Mediterranean. In the last 2000 years, four relatively wet intervals occurred between ca. 1800 and 1500 cal a BP (150–450 AD), 1350–1250 (600–700 AD), 1100–800 (850–1150 AD), and at ca. 90 cal a BP (1860 AD). Between ca. 4100 and 2500 cal a BP δ18O values are relatively high, with three prominent peaks indicating drier conditions at ca. 4100–4000 cal a BP, ca. 3500 and at ca. 3300 cal a BP. Four additional drier events are identified at 1850 (ca. 100 AD), 1400 (ca. 550 AD), 1150 (800 AD) and ca.750 cal a BP (1200 AD). The pollen record does not show changes in accordance with these episodes owing to the poor sensitivity of vegetation in this area, which is dominated by an orographic rainfall effect and where changes in altitudinal vegetation belts do not affect the pollen rain in the lake catchment. However, since ca. 900 cal a BP a significant decrease in the percentage arboreal pollen and in pollen concentrations suggest major deforestation produced by human activities. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
156.
Here we present a tephrostratigraphic record (core Co1202) recovered from the northeastern part of Lake Ohrid (Republics of Macedonia and Albania) reaching back to Marine Isotope Stage (MIS) 6. Overall ten horizons (OT0702‐1 to OT0702‐10) containing volcanic tephra have been recognised throughout the 14.94 m long sediment succession. Four tephra layers were visible at macroscopic inspection (OT0702‐4, OT0702‐6, OT0702‐8 and OT0702‐9), while the remaining six are cryptotephras (OT0702‐1, OT0702‐2, OT0702‐3, OT0702‐5, OT0702‐7 and OT0702‐10) identified from peaks in K, Zr and Sr intensities, magnetic susceptibility measurements, and washing and sieving of the sediments. Glass shards of tephra layers and cryptotephras were analysed with respect to their major element composition, and correlated to explosive eruptions of Italian volcanoes. The stratigraphy and the major element composition of tephra layers and cryptotephras allowed the correlation of OT0702‐1 to AD 472 or AD 512 eruptions of Somma‐Vesuvius, OT0702‐2 to the FL eruption of Mount Etna, OT0702‐3 to the Mercato from Somma‐Vesuvius, OT0702‐4 to SMP1‐e/Y‐3 eruption from the Campi Flegrei caldera, OT0702‐5 to the Codola eruption (Somma‐Vesuvius or Campi Flegrei), OT0702‐6 to the Campanian Ignimbrite/Y‐5 from the Campi Flegrei caldera, OT0702‐7 to the Green Tuff/Y‐6 eruption from Pantelleria Island, OT0702‐8 to the X‐5 eruption probably originating from the Campi Flegrei caldera, OT0702‐9 to the X‐6 eruption of generic Campanian origin, and OT0702‐10 to the P‐11 eruption from Pantelleria Island. The fairly well‐known ages of these tephra layers and parent eruptions provide new data on the dispersal and deposition of these tephras and, furthermore, allow the establishment of a chronological framework for core Co1202 for a first interpretation of major sedimentological changes. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   
157.
High‐resolution pollen, macrofossil and charcoal data, combined with accelerator mass spectrometry 14C dating and multivariate analysis, were used to reconstruct Holocene vegetation and fire dynamics at Urio Quattrocchi, a small lake in the supra‐mediterranean belt in the Nebrodi Mountains of Sicily (Italy). The data suggest that after 10 000 cal a BP increasing moisture availability supported closed forests with deciduous (Quercus cerris, Fagus sylvatica and Fraxinus spp.) and evergreen (Quercus ilex) species. Species‐rich closed forest persisted until 6850 cal a BP, when Neolithic activities caused a forest decline and affected plant diversity. Secondary forest with abundant Ilex aquifolium recovered between 6650 and 6000 cal a BP, indicating moist conditions. From 5000 cal a BP, agriculture and pastoralism led to the currently fragmented landscape with sparse deciduous forests (Quercus cerris). The study suggests that evergreen broadleaved species were more important at elevations above 1000 m a.s.l. before ca. 5000 cal a BP than subsequently, which might reflect less human impact or warmer‐than‐today climatic conditions between 10 000 and 5000 cal a BP. Despite land use since Neolithic times, deciduous supra‐mediterranean forests were never completely displaced from the Nebrodi Mountains, because of favourable moist conditions that persisted throughout the Holocene. Reconstructed vegetation dynamics document the absence of any pronounced mid‐ or late‐Holocene ‘aridification’ trend at the site, an issue which is controversially debated in Italy and the Mediterranean region. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
158.
This paper presents the results of the application of an ultrasonic telemetry system to the investigation of short‐term movements in the European spiny lobster, Palinurus elephas, in a coastal area of NW Sicily (Central Mediterranean Sea). Ten lobsters were tagged with miniaturized transmitters and released over a favourable habitat and their movements then recorded by means of nine automated receivers with the objective of investigating post‐release displacement, home‐range extension, movement patterns, activity rhythm and the influence of lunar light intensity on lobster activity. Acoustic detection data were used to assess activity and home range using estimates of horizontal and vertical movements and minimum convex polygons, respectively. Continuous wavelet transform (CWT) analysis was applied to time series of position data. Acoustic data from five of 10 lobsters were successfully recorded across a 78‐day study period between April and June 2008. All of them displayed an activity pattern characterized by diurnal sheltering and nocturnal foraging, with higher activity (i.e., longer distances travelled) at night. Their home range measured between 1629 and 8641 m2, and all lobsters relocated every 4.6 days on average, probably in search of unexploited feeding grounds. For this reason we hypothesize a nomadic movement pattern for our tagged lobsters. CWT analyses highlighted a 24‐h periodicity in lobster activity, with higher activity from sunset to sunrise. No clear influence of moon phase on lobster activity was detected.  相似文献   
159.
160.
Analogue models are used to investigate extension of a continental lithosphere weakened by asthenospheric melts percolating through the upper mantle, a process that has been hypothesised to control the opening of the Ligurian Tethys. Models were performed in a centrifuge apparatus and reproduced, by using materials such as sand and viscous mixtures, extension of 60-km thick, three-layer continental lithosphere floating above the asthenosphere. The percolated lithospheric mantle was assumed to be characterised by a rheological behaviour similar to that of the asthenosphere. Two sets of experiments investigated the influence on deformation of (1) the thickness of the percolated mantle and the associated strength contrast between the normal and weakened lithosphere, and (2) the lateral width of the weakened zone. Model results suggest that mantle percolation by asthenospheric melts is able to promote strong localised thinning of the continental lithosphere, provided that a significant thickness of the lithospheric mantle is weakened by migrating melts within a narrow region. Strain localisation is maximised for percolation of the whole lithospheric mantle and strong strength contrast between the normal and weakened lithosphere. Under these conditions, the thickness of the lithosphere may be reduced to less than 12 km in 3 Ma of extension. Conversely, localised thinning is strongly reduced if the thickness of the percolated zone is ≤1/3 of the thickness of the whole lithospheric mantle and/or the lithosphere is weakened over wide regions. Overall, model results support the working hypothesis that mantle percolation by asthenospheric melts is a controlling factor in the transition from distributed continental deformation to localised oceanic spreading.  相似文献   
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