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Hydrogeology Journal - This study aims to determine the groundwater flow in a large area of the Venice (northeast Italy) lagoon that is under great anthropogenic pressure, which is influencing the... 相似文献
536.
Effects of climate and density-dependent factors on population dynamics of the pine processionary moth in the Southern Alps 总被引:1,自引:0,他引:1
Giovanni Tamburini Lorenzo Marini Klaus Hellrigl Cristina Salvadori Andrea Battisti 《Climatic change》2013,121(4):701-712
Forest pest populations can fluctuate dramatically in relation to climate and density-dependent factors. Although the distributional range of the pine processionary moth Thaumetopoea pityocampa (Lepidoptera Notodontidae) appears to be expanding northward and upslope with climate warming, the relative importance of climate and endogenous, density-dependent factors has not been clearly documented. We analyzed the population dynamics of the moth using long-term data from two provinces in the Southern Alps (Trento: 1990–2009, Bolzano/Bozen: 1975–2011) to evaluate the relative importance of climate and density-dependent factors as regional drivers. Both summer temperatures and rainfall significantly affected population growth rate, with different outcomes depending on the local conditions. Although previous studies indicated that low winter temperatures have negative effects on insect performance, our analyses did not show any negative effect on the population dynamics. A negative density dependent feedback with a 1-year lag emerged as the most important factor driving the population dynamics in both regions. Potential mechanisms explaining the observed negative density feedback include deterioration of host quality, increased mortality caused by pathogens, and increase of prolonged diapause as an adaptive mechanism to escape adverse conditions. 相似文献
537.
Marco G. Malusà Igor M. Villa Giovanni Vezzoli Eduardo Garzanti 《Earth and Planetary Science Letters》2011,301(1-2):324-336
Tectonic reconstructions and quantitative models of landscape evolution are increasingly based on detailed analysis of detrital systems. Since the definition of closure temperature in the 1960s, mineral ages of low-temperature geochronometers are traditionally interpreted as the result of cooling induced by erosion, whose rate is a simple, unique function of age patterns. Such an approach can lead to infer paradoxically high erosion rates that conflict with compelling geological evidence from sediment thickness in basins. This indicates that tectonic and landscape models that solely interpret mineral ages as due to cooling during exhumation may not be valid.Here we propose a new approach that takes into account the effects of both crystallization and exhumational cooling on geochronometers, from U–Pb on zircon to fission tracks on apatite. We first model the mechanical erosion of an unroofing magmatic complex and the resulting accumulation and burial of the eroded units in reverse order in the basin. Detrital mineral ages follow a regular pattern downsection. Some mineral ages, such as e.g. U–Pb ages of zircons, cluster around the “magmatic age”, i.e. the crystallization of the magma. Its value is constant along the stratigraphic column in the sedimentary basin; we refer to this behavior as “stationary age peak”. Some other mineral ages, such as e.g. apatite fission-track ages, are often younger than the magmatic age. When they vary smoothly with depth, they define a “moving age peak”, which is the only possible effect of undisturbed cooling during overburden removal, and can therefore be used to calculate an erosion rate.The predictions of our model were tested in detail on the extremely well-studied Bregaglia (Bergell) orogenic pluton in the Alps, and on the sedimentary succession derived from its erosion, the Gonfolite Group. The consistency between predicted and observed age patterns validates the model. Our results resolve a long-standing paradox in quantitative modelling of erosion–sedimentation, namely the scarcity of sediment during apparently fast erosion. Starved basins are the observational baseline, and modelling must be tuned to include a correct analysis of detrital mineral geochronology in order to reconcile perceived discrepancies between stratigraphical and geochronological information. In addition, our data demonstrate that volcanoes were active on top of the growing Oligocene Alps.This study illustrates rigorous criteria for detrital mineral geochronology that are applicable to any geological setting, including magmatic arcs and collision orogens, and provides fundamental interpretive keys to solve complex puzzles and apparent paradoxes in geological reconstructions. 相似文献
538.
Nazzareno Diodato Gianni Bellocchi Nunzio Romano Giovanni Battista Chirico 《Climatic change》2011,108(3):591-599
Rainfall and overland flow are fundamental processes for Earth’s ecosystems but can also be land disturbing forces, particularly
when triggered by extreme hydro-meteorological events. Examples of these extremes are rainstorms and related phenomena due
to rainfall aggressiveness. They produce high-impact land processes such as soil erosion and nutrient losses. Economic and
social consequences of these processes can be quite severe. However, hydrological extremes and their environmental implications
are still poorly understood, particularly if analyzed in the context of climate change. Here, we analyze a 300 year long times
series of historical rainfall patterns across the Mediterranean in the last three centuries and we investigate changes in
the erosive forcing as related to climate changes. Our results show that the erosive forcing increased towards the end of
the Little Ice Age (~1850) over western and central Mediterranean and that has been increasing in the recent warming period
at low Mediterranean latitudes, due to a higher frequency of intensive storms. Such increased concentrated precipitation may
lead to an intensification of land degradation processes triggered by soil erosion and transport across a range of scales
from hillslopes to small catchments. 相似文献
539.
Assessment of ground motion variability and its effects on seismic hazard analysis: a case study for iceland 总被引:1,自引:1,他引:0
Teraphan Ornthammarath John Douglas Ragnar Sigbj?rnsson Carlo Giovanni Lai 《Bulletin of Earthquake Engineering》2011,9(4):931-953
Probabilistic seismic hazard analysis (PSHA) generally relies on the basic assumption that ground motion prediction equations
(GMPEs) developed for other similar tectonic regions can be adopted in the considered area. This implies that observed ground
motion and its variability at considered sites could be modelled by the selected GMPEs. Until now ground-motion variability
has been taken into account in PSHA by integrating over the standard deviation reported in GMPEs, which significantly affects
estimated ground motions, especially at very low probabilities of exceedance. To provide insight on this issue, ground-motion
variability in the South Iceland Seismic Zone (SISZ), where many ground-motion records are available, is assessed. Three statistical
methods are applied to separate the aleatory variability into source (inter-event), site (inter-site) and residual (intra-event
and intra-site) components. Furthermore, the current PSHA procedure that makes the ergodic assumption of equality between
spatially and temporal variability is examined. In contrast to the ergodic assumption, several recent studies show that the
observed ground-motion variability at an individual location is lower than that implied by the standard deviation of a GMPE.
This could imply a mishandling of aleatory uncertainty in PSHA by ignoring spatial variability and by mixing aleatory and
epistemic uncertainties in the computation of sigma. Station correction coefficients are introduced in order to capture site
effects at different stations. The introduction of the non-ergodic assumption in PSHA leads to larger epistemic uncertainty,
although this is not the same as traditional epistemic uncertainty modelled using different GMPEs. The epistemic uncertainty
due to the site correction coefficients (i.e. mean residuals) could be better constrained for future events if more information
regarding the characteristics of these seismic sources and path dependence could be obtained. 相似文献
540.
Giovanni Fontana Conall Mac Niocaill Richard J. Brown R. Stephen J. Sparks Matthew Field 《Bulletin of Volcanology》2011,73(8):1063-1083
Palaeomagnetic techniques for estimating the emplacement temperatures of volcanic deposits have been applied to pyroclastic
and volcaniclastic deposits in kimberlite pipes in southern Africa. Lithic clasts were sampled from a variety of lithofacies
from three pipes for which the internal geology is well constrained (the Cretaceous A/K1 pipe, Orapa Mine, Botswana, and the
Cambrian K1 and K2 pipes, Venetia Mine, South Africa). The sampled deposits included massive and layered vent-filling breccias
with varying abundances of lithic inclusions, layered crater-filling pyroclastic deposits, talus breccias and volcaniclastic
breccias. Basalt lithic clasts in the layered and massive vent-filling pyroclastic deposits in the A/K1 pipe at Orapa were
emplaced at >570°C, in the pyroclastic crater-filling deposits at 200–440°C and in crater-filling talus breccias and volcaniclastic
breccias at <180°C. The results from the K1 and K2 pipes at Venetia suggest emplacement temperatures for the vent-filling
breccias of 260°C to >560°C, although the interpretation of these results is hampered by the presence of Mesozoic magnetic
overprints. These temperatures are comparable to the estimated emplacement temperatures of other kimberlite deposits and fall
within the proposed stability field for common interstitial matrix mineral assemblages within vent-filling volcaniclastic
kimberlites. The temperatures are also comparable to those obtained for pyroclastic deposits in other, silicic, volcanic systems.
Because the lithic content of the studied deposits is 10–30%, the initial bulk temperature of the pyroclastic mixture of cold
lithic clasts and juvenile kimberlite magma could have been 300–400°C hotter than the palaeomagnetic estimates. Together with
the discovery of welded and agglutinated juvenile pyroclasts in some pyroclastic kimberlites, the palaeomagnetic results indicate
that there are examples of kimberlites where phreatomagmatism did not play a major role in the generation of the pyroclastic
deposits. This study indicates that palaeomagnetic methods can successfully distinguish differences in the emplacement temperatures
of different kimberlite facies. 相似文献