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91.
Trophic network model of the Northern Adriatic Sea: Analysis of an exploited and eutrophic ecosystem
Alberto Barausse Alessandro Duci Carlotta Mazzoldi Yuri Artioli Luca Palmeri 《Estuarine, Coastal and Shelf Science》2009,83(4):577-590
A quantitative model of the trophic network of Northern Adriatic Sea marine ecosystem during the 1990s has been constructed, with the goal of analysing its trophic structure, identifying the key trophic groups and assessing the anthropogenic impacts on the ecosystem using the Ecopath modelling protocol. The Northern Adriatic Sea is an eutrophic, shallow basin, and one of the most heavily fished areas in the Mediterranean Sea. The network aggregation into discrete trophic levels sensu Lindeman shows that low trophic levels dominate biomass and energy flows, with 40% of the total system throughput flowing out from trophic level 2. Instead, upper trophic levels appear bottom-up controlled, highly depleted and not exerting any control on the trophic network, as shown by mixed trophic impact-based analyses. Microbial loop is comparable to grazing with respect to the magnitude of flows involved, as 66% of the trophic network flows originate from detritus, which is mainly consumed by bacteria. Key trophic groups are plankton groups, macro-crustaceans and detritus, and other r-selected organisms like squids and small pelagics, which have a great influence on the ecosystem. In particular, zooplankton acts as a bottleneck for energy flows, limiting the energy from the low trophic levels effectively reaching the upper food web. The high pelagic production caused by eutrophication sustains high fishery landings and impressive discard quantities, as well as the benthic compartment. Overall, the ecosystem appears quite productive and in a stressed and developmental status. Model results and comparisons with few existing historical data suggest that the low maturity and stressed state of the Northern Adriatic Sea are not only due to natural characteristics, but mainly to anthropogenic pressures. 相似文献
92.
The gas transport through non-volatile random porous media is investigated numerically. We extend our previous research of the transport of molecules inside the uppermost layer of a cometary surface (
[Skorov and Rickman, 1995] and [Skorov et al., 2001]). We assess the validity of the simplified capillary model and its assumptions to simulate the gas flux trough the porous dust mantle as it has been applied in cometary physics. A microphysical computational model for molecular transport in random porous media formed by packed spheres is presented. The main transport characteristics such as the mean free path distribution and the permeability are calculated for a wide range of model parameters and compared with those obtained by more idealized models. The focus in this comparison is on limitations inherent in the capillary model. Finally a practical way is suggested to adjust the algebraic Clausing formula taking into consideration the nonlinear dependence of permeability on layer porosity. The retrieved dependence allows us to accurately calculate the permeability of layers whose thickness and porosity vary in the range of values expected for the near-surface regions of a cometary nucleus. 相似文献
93.
How contact metamorphism can trigger global climate changes: Modeling gas generation around igneous sills in sedimentary basins 总被引:2,自引:0,他引:2
Ingrid Aarnes Henrik Svensen Yuri Y. Podladchikov 《Geochimica et cosmochimica acta》2010,74(24):7179-7195
Large volumes of greenhouse gases such as CH4 and CO2 form by contact metamorphism of organic-rich sediments in aureoles around sill intrusions in sedimentary basins. Thermogenic gas generation and dehydration reactions in shale are treated numerically in order to quantify basin-scale devolatilization. We show that aureole thicknesses, defined as the zone of elevated metamorphism relative to the background level, vary within 30-250% of the sill thickness, depending on the temperature of the host-rock and intrusion, besides the sill thickness. In shales with total organic carbon content of >5 wt.%, CH4 is the dominant volatile (85-135 kg/m3) generated through organic cracking, relative to H2O-generation from dehydration reactions (30-110 kg/m3). Even using conservative estimates of melt volumes, extrapolation of our results to the scale of sill complexes in a sedimentary basin indicates that devolatilization can have generated ∼2700-16200 Gt CH4 in the Karoo Basin (South Africa), and ∼600-3500 Gt CH4 in the Vøring and Møre basins (offshore Norway). The generation of volatiles is occurring on a time-scale of 10-1000 years within an aureole of a single sill, which makes the rate of sill emplacement the time-constraining factor on a basin-scale. This study demonstrates that thousands of gigatons of potent greenhouse gases like methane can be generated during emplacement of Large Igneous Provinces in sedimentary basins. 相似文献
94.
Julia Semprich Nina S. C. Simon Yuri Yu. Podladchikov 《International Journal of Earth Sciences》2010,99(7):1487-1510
Constraints on density as a function of pressure, temperature, and composition are crucial to understand isostatic movements
during geodynamic processes. Here, we provide a systematic series of density diagrams extracted from thermodynamic calculations
for a variety of crustal compositions within a wide P–T range. We quantify systematic density changes in collisional settings for relevant compositional variations and attempt to
simplify the density–composition relationships. Rock densities depend strongly on pressure, temperature, and composition.
Densities at some selected pressure–temperature conditions increase linearly with increasing Al2O3 as well as MgO/FeO contents in pelitic rocks. Al- and Fe-rich pelites yield the highest densities, which is mostly due to
the formation of garnet but also depends on other minerals and changes of reactions. The effect of loading on densities is
investigated, and we show that for deep burial, a meta-pelite rich in Fe and Mg yields much larger density changes than a
dry basalt and that the burial of such a rock with a composition close to typical lower crust may result in significant negative
buoyancy. Metamorphism of hydrous lower crust due to pressurization and heating thus leads to densification of thickened lower
crust, while heating of dry crust leads to a decrease in density. Hence, water-loaded isostatic subsidence due to metamorphism
of water-saturated lower crust is substantial and increases with the thickness and depth of the reacting layer, while dry
compositions show much less or only transient densification and subsidence. The density change due to thermal expansion, an
extensively used concept in geodynamic models, predicts uplift under the same P–T conditions and is an order of magnitude smaller than the density variation calculated from petrologically consistent diagrams. 相似文献
95.
The big Comacchio lagoons (NW Adriatic coast) have been experiencing a super-dense, long-term bloom of picocyanobacteria (PCB)
since 1985. This bloom has caused profound transformations in their ecosystem and has resulted in the loss of valuable fish
and clam resources. The composition, density and seasonal dynamics of this bloom and its impact on the ecosystem were studied
between spring and autumn 1995 and in the summer of 2001. The density of the blooming phytoplankton assemblages varied from
8 to 35 × 106 cells ml−1, and biomass from 20 to 40 g m−3, thus demonstrating a quasi-stable status since 1993. The share of pico + nanocyanobacterial fraction of the total phytoplankton
biomass was 98% in spring to early summer, and 92% in autumn. The remaining 0.2–5% comprised eukaryotic nano-algae. All components
of the animal food web were found to be drastically depleted in the lagoons. Their biomass range in the open lagoons areas
were: 2 to 20 mg m−3 of microzooplankton, 10 to 40 mg m−3 mesozooplankton, and 5 to 12 g m−2 macrozoobenthos. The share of filtering fauna in the whole ecosystem metabolism was less than 2%. The malfunction of the
deteriorated animal food web resulted in the hyper-accumulation of non-grazed microplankton biomass and detritus in the water
column and in bottom sediments. The sequence brought the acceleration of sulfide production and the accumulation of acid soluble
sulfides in the upper sediment layer of up to 700–800 mg S dm−3 of wet silt. The results of this study provide evidence that the state of ecological collapse continues in the lagoons since
1993. 相似文献
96.
Mollisols properties and changes in Ukraine and China 总被引:4,自引:2,他引:2
Soils are the foundation of civilizations and the basis for human food production.Mollisols in Ukraine and Northeast China are two out of the four major Mollisol regions in the world.The natural areas from which Mollisols developed are the prairies and steppes that experience temperate and freezing conditions.This review paper introduces the general climate,vegetation,and topography of Mollisols regions in Ukraine and Northeast China,analyzes their properties,including soil texture,soil organic matter content,soil bulk density,pH,cation exchange capacity and other chemical properties,and compares the property changes and management practices of Mollisols in relation to sustainable grain production. 相似文献
97.
98.
Skorov Yuri V. Keller Horst U. Jorda Laurent Davidsson Bjørn J. R. 《Earth, Moon, and Planets》2002,90(1-4):293-303
In this work, we continue revising the theoretical basis ofnumerical models describing the transport of matter andenergy inside
a porous dust-ice mixture at low temperature. Amodel of a light-absorbing near-surface layer of a comet nucleus isinvestigated.
Gas transport is considered simultaneously with thesolution of the general heat transfer equation. Thequasi-stationary temperature
distribution and the H2O massflux and sublimation rate are computed for a nucleus model ofcomet 19P/Borrelly at the Deep Space 1 (DS1) encounter.
Theenergy is deposited in a layer of about 20 particle radii: Thiscorresponds to a solid-state greenhouse effect. The surfacetemperature
of the layer-absorbing model as well as the gasproduction rate are significantly smaller than the ones in thesurface-absorbing
model. An active fraction of 40–50% would berequired to explain the observed water production rate ofP/Borrelly with our layer-absorption
model at the time of the DS1encounter. 相似文献
99.
Adriane Steinacker † Yuri A. Shchekinov 《Monthly notices of the Royal Astronomical Society》2001,325(1):208-220
Within a framework of 2D magnetohydrodynamic (MHD) simulations, we explore the dynamical regimes initiated by a supernova explosion in a magnetized stratified interstellar medium (ISM). We concentrate on the formation of large-scale magnetic structures and outflows connected with the Parker instability. For the sake of simplicity we only show models with a fixed explosion energy corresponding to a single supernova (SN) occurring in host galaxies with different fixed values of the gravitational acceleration g and different ratios of specific heats. We show that in general, depending on these two parameters, three different regimes are possible: a slowly growing Parker instability on time-scales much longer than the galactic rotation period for small g; the Parker instability growing at roughly the rotation period, which for ratios of specific heats larger than one is accompanied by an outflow resulting from the explosion for intermediate g; and a rapidly growing instability and a strong blow-out flow for large g . By means of numerical simulations and analytical estimates we show that the explosion energy and gravitational acceleration which separate the three regimes scale as Eg 2 ∼constant in the 2D case. We expect that in the 3D case this scaling law is Eg 3 ∼constant . Our simulations demonstrate furthermore that a single SN explosion can lead to the growth of multiple Parker loops in the disc and large-scale magnetic field loops in the halo, extending over 2–3 kpc horizontally and up to 3 kpc vertically above the mid-plane of the disc. 相似文献
100.
The evolution of ground thermal state has been studied to assess impacts of current climatic warming on permafrost in Central Yakutia. The analysis of long-term data of regional weather stations has revealed one of the highest increasing trends in mean annual air temperature in northern Russia. A forecast of surface air temperature fluctuations has been made by applying a frequency analysis method. Monitoring of ground thermal conditions allows us to identify inter-annual and long-term variability among a wide range of natural conditions. Experimental research has indicated a long-term dynamics of ground thermal state evolution: ground temperatures at the depth of zero annual amplitude and seasonally thawed layer depth. Long-term variability of thaw depth shows near-zero to weak positive trends in small valleys in contrast to weak negative trends on slopes. With significant climatic warming, the thermal state of near-surface layers of permafrost demonstrates steadiness. Anthropogenic impacts on ground thermal regime in various terrain types have been qualitatively evaluated. Clear-cutting, ground cover stripping, and post-fire deforestation in inter-alas type terrains result in a significant increase of temperature and seasonal ground thaw depth, as well as adverse cryogenic processes. The dynamics of mean annual ground temperature in slash and burn sites have been evaluated in reference to stages of successive vegetation recovery. 相似文献