排序方式: 共有36条查询结果,搜索用时 500 毫秒
11.
Nelson A.F. Miranda Renzo Perissinotto Christopher C. Appleton 《Estuarine, Coastal and Shelf Science》2011,91(3):442-449
Gut fluorescence and carbon budget techniques were applied to Tarebia granifera (shell height 10–12 mm) at the iSimangaliso Wetland Park, a UNESCO World Heritage Site. This snail has recently invaded a number of estuaries in northern KwaZulu-Natal, where it reaches densities of over 1000 ind. m?2 and becomes a dominant component of the benthic community. Its rapid establishment and spread have raised concerns about potential top-down impacts on the ecosystem. This study shows that T. granifera can utilize large amounts of microphytobenthos (MPB) in addition to detritus. In situ total available MPB pigment concentrations ranged from 11.6 to 110.5 mg pigm. m?2. T. granifera’s gut pigment content ranged from 54 to 1672 μg pigm. ind?1. Gut evacuation rates (k) ranged from 0.36 to 0.62 h?1 (R2 range: 16.2–35.2, P < 0.05). Individual ingestion rates ranged from 6.6 to 30.4 μg pigm. ind.?1 d?1. T. granifera was estimated to consume from 0.5 to 35% of the total available MPB biomass per day, or 1.2–68% of the daily primary benthic production. The carbon component estimated from the gut fluorescence technique contributed 8.7–40.9% of the total gut organic carbon content. The average carbon daily ration contributed by microalgal biomass was ≈16% body carbon per day. Variability in the data was attributed to the complex feeding history of snails. Further studies are needed to validate these results and provide more information on the ecological impact of T. granifera on this wetland and other similar invaded ecosystems, both estuarine and freshwater. 相似文献
12.
Decline of traditional landscape in a protected area of the southwestern Alps: The fate of enclosed pasture patches in the land mosaic shift 总被引:1,自引:0,他引:1
【Title】
【Author】
【Addresses】1
Traditional landscape elements such as pasture patches enclosed in a forest matrix are progressively disappearing throughout the European Alps. We assessed the land mosaic shift of a protected area located in the western Italian Alps. In particular, the dynamics of pasture patches were studied at both landscape and stand level. Land-cover mapping through object-oriented analysis of historical aerial photographs was used to assess land-cover changes between 1954 and 2000. Spatial statistics were used to quantify landscape patterns, and field samplings within pasture patches were used to explore tree regeneration structure and composition. Our results showed a significant increase in the number of pasture patches caused by their fragmentation following forest expansion. The total surface area of pasture patches decreased by 43% and their core area decreased by 94%. The encroachment of trees on less accessible areas of the pasture patches caused a reduction of patch shape at landscape scale. The gap filling process started 40-50 years ago and began with an early invasion of light demanding species like sycamore maple (Acer pseudoplatanus L.) and common ash (Fraxinus excelsior L.), followed by European beech (Fagus sylvatica L.) and secondarily silver fir (Abies alba Mill.). Traditional land-use and population decline in the Pesio Valley led to a reduction in ecotone areas. A transition to a more homogeneous landscape is expected in the next decades. Given the cultural and productive nature of these mountain meadow-pasture communities, extensive livestock grazing systems could be used to manage their future conservation. 相似文献
【Author】
【Addresses】1
Traditional landscape elements such as pasture patches enclosed in a forest matrix are progressively disappearing throughout the European Alps. We assessed the land mosaic shift of a protected area located in the western Italian Alps. In particular, the dynamics of pasture patches were studied at both landscape and stand level. Land-cover mapping through object-oriented analysis of historical aerial photographs was used to assess land-cover changes between 1954 and 2000. Spatial statistics were used to quantify landscape patterns, and field samplings within pasture patches were used to explore tree regeneration structure and composition. Our results showed a significant increase in the number of pasture patches caused by their fragmentation following forest expansion. The total surface area of pasture patches decreased by 43% and their core area decreased by 94%. The encroachment of trees on less accessible areas of the pasture patches caused a reduction of patch shape at landscape scale. The gap filling process started 40-50 years ago and began with an early invasion of light demanding species like sycamore maple (Acer pseudoplatanus L.) and common ash (Fraxinus excelsior L.), followed by European beech (Fagus sylvatica L.) and secondarily silver fir (Abies alba Mill.). Traditional land-use and population decline in the Pesio Valley led to a reduction in ecotone areas. A transition to a more homogeneous landscape is expected in the next decades. Given the cultural and productive nature of these mountain meadow-pasture communities, extensive livestock grazing systems could be used to manage their future conservation. 相似文献
13.
The Averno 2 fissure eruption: a recent small-size explosive event at the Campi Flegrei Caldera (Italy) 总被引:1,自引:0,他引:1
Mauro Antonio Di Vito Ilenia Arienzo Giuseppe Braia Lucia Civetta Massimo D’Antonio Valeria Di Renzo Giovanni Orsi 《Bulletin of Volcanology》2011,73(3):295-320
The Averno 2 eruption (3,700 ± 50 a B.P.) was an explosive low-magnitude event characterized by magmatic and phreatomagmatic
explosions, generating mainly fall and surge beds, respectively. It occurred in the Western sector of the Campi Flegrei caldera
(Campanian Region, South Italy) at the intersection of two active fault systems, oriented NE and NW. The morphologically complex
crater area, largely filled by the Averno lake, resulted from vent activation and migration along the NE-trending fault system.
The eruption generated a complex sequence of pyroclastic deposits, including pumice fall deposits in the lower portion, and
prevailing surge beds in the intermediate-upper portion. The pyroclastic sequence has been studied through stratigraphical,
morphostructural and petrological investigations, and subdivided into three members named A through C. Member A was emplaced
during the first phase of the eruption mainly by magmatic explosions which generated columns reaching a maximum height of
10 km. During this phase the eruption reached its climax with a mass discharge rate of 3.2 106 kg/s. Intense fracturing and fault activation favored entry of a significant amount of water into the system, which produced
explosions driven by variably efficient water-magma interaction. These explosions generated wet to dry surge deposits that
emplaced Member B and C, respectively. Isopachs and isopleths maps, as well as areal distribution of ballistic fragments and
facies variation of surge deposits allow definition of four vents that opened along a NE oriented, 2 km long fissure. The
total volume of magma extruded during the eruption has been estimated at about 0.07 km3 (DRE). The erupted products range in composition from initial, weakly peralkaline alkali-trachyte, to last-emplaced alkali-trachyte.
Isotopic data and modeling suggest that mixing occurred during the Averno 2 eruption between a more evolved, less radiogenic
stored magma, and a less evolved, more radiogenic magma that entered the shallow reservoir to trigger the eruption. The early
phases of the eruption, during which the vent migrated from SW to the center of the present lake, were fed by the more evolved,
uppermost magma, while the following phases extruded the less evolved, lowermost magma. Integration of the geological and
petrological results suggests that the Averno 2 complex eruption was fed from a dyke-shaped shallow reservoir intruded into
the NE-SW fault system bordering to the west the La Starza resurgent block, within the caldera floor. 相似文献
14.
A new hydrostratigraphic model of Venice area (Italy) 总被引:3,自引:3,他引:0
Matteo Cultrera Renzo Antonelli Giordano Teza Silvia Castellaro 《Environmental Earth Sciences》2012,66(4):1021-1030
Two environmental problems affect the Venice area: subsidence, which has been increasing due to the intensive water abstraction after the Second World War, and contamination of the soil and shallow aquifers. In order to address these problems, which are decisive factors in the entire Venetian ecosystem, the aquifer structure must be known in detail. The lithologic data are abundant and of good quality up to a depth of 50 m, whereas boreholes beyond this depth are much rarer and more dispersed, making their associated lithological data unreliable. This work, which uses the available data together with fast and low cost passive seismic measurements, provides an improved understanding of the deeper hydrogeologic domain. For this purpose, a MATLAB package (Modalstrata) has been developed to improve the correlation of the stratigraphic succession for each selected homogeneous sub-area and applied to obtain a new, upgraded hydrostratigraphic model. The horizontal to vertical spectral ratio passive seismic surveys have confirmed the lateral correlations among the sample areas at least for the two main aquifer horizons. Analysis and comparisons of several previous studies performed on the data related to the only drilling continuous coring 951 m deep in the Tronchetto Island (Venice), have allowed a satisfactory validation of the proposed hydrogeological model. 相似文献
15.
High resolution radar rainfall fields and a distributed hydrologic model are used to evaluate the sensitivity of flood and flash flood simulations to spatial aggregation of rainfall and soil properties at catchment scales ranging from 75 to 983 km2. Hydrologic modeling is based on a Hortonian infiltration model and a network-based representation of hillslope and channel flow. The investigation focuses on three extreme flood and flash flood events occurred on the Sesia river basin, North Western Italy, which are analysed by using four aggregation lengths ranging from 1 to 16 km. The influence of rainfall spatial aggregation is examined by using the flow distance as a spatial coordinate, hence emphasising the role of river network in the averaging of space–time rainfall. The effects of reduced and distorted rainfall spatial variability on peak discharge have been found particularly severe for the flash flood events, with peak errors up to 35% for rainfall aggregation of 16 km and at 983 km2 catchment size. Effects are particularly remarkable when significant structured rainfall variability combines with relatively important infiltration volumes due to dry initial conditions, as this emphasises the non-linear character of the rainfall–runoff relationship. In general, these results confirm that the correct estimate of rainfall volume is not enough for the accurate reproduction of flash flood events characterised by large and structured rainfall spatial variability, even at catchment scales around 250 km2. However, accurate rainfall volume estimation may suffice for less spatially variable flood events. Increasing the soil properties aggregation length exerts similar effects on peak discharge errors as increasing the rainfall aggregation length, for the cases considered here and after rescaling to preserve the rainfall volume. Moreover, peak discharge errors are roughly proportional to runoff volume errors, which indicates that the shape of the flood wave is influenced in a limited way by modifying the detail of the soil property spatial representation. Conversely, rainfall aggregation may exert a pronounced influence on the discharge peak by reshaping the spatial organisation of the runoff volumes and without a comparable impact on the runoff volumes. 相似文献
16.
Rosa Anna Corsaro Lucia Civetta Valeria Di Renzo Lucia Miraglia 《Bulletin of Volcanology》2009,71(7):781-793
Following the 2001 and 2002–2003 flank eruptions, activity resumed at Mt. Etna on 7 September 2004 and lasted for about 6 months.
This paper presents new petrographic, major and trace element, and Sr–Nd isotope data from sequential samples collected during
the entire 2004–2005 eruption. The progressive change of lava composition allowed defining three phases that correspond to
different processes controlling magma dynamics inside the central volcano conduits. The compositional variability of products
erupted up to 24 September is well reproduced by a fractional crystallization model that involves magma already stored at
shallow depth since the 2002–2003 eruption. The progressive mixing of this magma with a distinct new one rising within the
central conduits is clearly revealed by the composition of the products erupted from 24 September to 15 October. After 15
October, the contribution from the new magma gradually becomes predominant, and the efficiency of the mixing process ensures
the emission of homogeneous products up to the end of the eruption. Our results give insights into the complex conditions
of magma storage and evolution in the shallow plumbing system of Mt. Etna during a flank eruption. Furthermore, they confirm
that the 2004–2005 activity at Etna was triggered by regional movements of the eastern flank of the volcano. They caused the
opening of a complex fracture zone extending ESE which drained a magma stored at shallow depth since the 2002–2003 eruption.
This process favored the ascent of a different magma in the central conduits, which began to be erupted on 24 September without
any significant change in eruptive style, deformation, and seismicity until the end of eruption. 相似文献
17.
Talc and/or pyrophyllite have been detected as suspended particulates in the waters of the Ionian Sea (eastern Mediterranean). Differing from similar findings reported in some recent works by many authors, the presence of these silicates is completely attributable to unavoidable contamination during collection and analytical processing of the water samples. 相似文献
18.
19.
Renzo Sancisi Filippo Fraternali Tom Oosterloo Thijs van der Hulst 《Astronomy and Astrophysics Review》2008,15(3):189-223
Evidence for the accretion of cold gas in galaxies has been rapidly accumulating in the past years. HI observations of galaxies and their environment have brought to light new facts and phenomena which are evidence of ongoing
or recent accretion: (1) A large number of galaxies are accompanied by gas-rich dwarfs or are surrounded by HI cloud complexes, tails and filaments. This suggests ongoing minor mergers and recent arrival of external gas. It may be regarded,
therefore, as direct evidence of cold gas accretion in the local universe. It is probably the same kind of phenomenon of material
infall as the stellar streams observed in the halos of our galaxy and M 31. (2) Considerable amounts of extra-planar HI have been found in nearby spiral galaxies. While a large fraction of this gas is undoubtedly produced by galactic fountains,
it is likely that a part of it is of extragalactic origin. Also the Milky Way has extra-planar gas complexes: the Intermediate-
and High-Velocity Clouds (IVCs and HVCs). (3) Spirals are known to have extended and warped outer layers of HI. It is not clear how these have formed, and how and for how long the warps can be sustained. Gas infall has been proposed
as the origin. (4) The majority of galactic disks are lopsided in their morphology as well as in their kinematics. Also here
recent accretion has been advocated as a possible cause. In our view, accretion takes place both through the arrival and merging
of gas-rich satellites and through gas infall from the intergalactic medium (IGM). The new gas could be added to the halo
or be deposited in the outer parts of galaxies and form reservoirs for replenishing the inner parts and feeding star formation.
The infall may have observable effects on the disk such as bursts of star formation and lopsidedness. We infer a mean “visible”
accretion rate of cold gas in galaxies of at least . In order to reach the accretion rates needed to sustain the observed star formation (), additional infall of large amounts of gas from the IGM seems to be required. 相似文献
20.
To which extent do wildfires affect runoff production, soil erosion and sediment transport in upland catchments? This transient effect is investigated here by combining data of long term precipitation, sediment yield and wildfire records with a fine resolution spatially distributed modeling approach to flow generation and surface erosion. The model accounts for changes in the structure and properties of soil and vegetation cover by combining the tube-flux approach to topographic watershed partition with a parsimonious parametrization of hydrologic processes. This model is used to predict hydrologic and sediment fluxes for nine small catchments in Saint Gabriel mountains of southern California under control (pre-fire) and altered (post-fire) conditions. Simulation runs using a 45 years record of hourly precipitation show the passage of fire to significantly modify catchment response to storms with a major effect on erosion and flood flows. The probability of occurrence of major floods in the post-fire season is shown to increase up to an order of magnitude under same precipitation conditions. Also, the expected anomaly of sediment yield can increase dramatically the desertification hazard in upland wildfire prone areas. One should further consider the role of firefloods produced by the combined occurrence of wildfires and storms as a fundamental source of non-stationarity in the assessment of hydrologic hazard. 相似文献