Fractal behavior in space and time in a simplified model of fluvial landform evolution     

Jon D. Pelletier   《Geomorphology》2007,91(3-4):291

Two general approaches have been applied to understanding the fractal structure of fluvial topography: (1) deterministic, process-based models, and (2) stochastic partial differential equations (PDE). Deterministic models reproduce the fractal behavior of fluvial topography but have two limitations: they often underestimate the amount of lateral valley and ridge migration that occurs in nature, and the complexity has made it difficult to identify the precise origin of fractal behavior in fluvial landscapes. The simplicity of stochastic PDE models has made them useful for investigating fractal behavior, but they incorrectly suggest that fractal behavior is only possible with stochastic forcing. In this paper I investigate whether simplified, deterministic PDE models of landform evolution also exhibit fractal behavior and other features of complexity (i.e. deterministic chaos). These models are based on the KPZ equation, well known in the physics literature. This equation combines diffusion (i.e. hillslope processes) and nonlinear advection (i.e. bedrock or alluvial channel incision). Two models are considered: (1) a deterministic model with uniform erodibility and random initial topography, and (2) a deterministic model with random erodibility and uniform initial topography. Results illustrate that both of these deterministic models exhibit fractal behavior and deterministic chaos. In this context, chaotic behavior means that valley and ridge migration and nonlinear amplification of small perturbations in these models prevent an ideal steady state landscape from ever developing in the large-system limit. These results suggest that fractal structure and deterministic chaos are intrinsic features of the evolution of fluvial landforms, and that these features result from an inverse cascade of energy from small to large wavelengths in drainage basins. This inverse cascade differs from the direct cascade of three-dimensional turbulence in which energy flows from large to small wavelengths.  相似文献   

Management under uncertainty: defining strategies for reducing overexploitation   总被引：1，自引：1，他引：1  

Pelletier  D.; Laurec  A. 《ICES Journal of Marine Science》1992,49(4):389-401

  相似文献   

Of laws and limits: An ecological economic perspective on redressing the failure of contemporary global environmental governance     

Nathan Pelletier 《Global Environmental Change》2010,20(2):220-228

The persistent failures of international environmental governance initiatives to halt the degradation of the global commons are directly linked to the implicit worldview and assumptions fueling the proliferation of industrial society. These include an instrumental conception on non-human nature, rampant materialism, technological optimism, and an expansionary economics premised on the axiomatic necessity of unconstrained growth. Permeating contemporary environmental governance regimes, it is argued that these premises are fundamentally incompatible with the requirements of environmental sustainability. Proceeding from the perspective of ecological economics, it is further argued that achieving environmental sustainability in industrial society requires foremost that we restructure and constrain the scale of economic activities relative to global biocapacity. It is concluded that a scale-based approach to governing the environmental commons, operationalized by a strong world environment organization, offers at least a partial solution to this conundrum.  相似文献   

Flooding of the Saguenay region in 1996. Part 2: Aux Sables River flood mitigation and environmental impact assessment     

AlQasimi  Eman  Pelletier  Pierre  Mahdi  Tew-Fik 《Natural Hazards》2019,99(1):17-37

Natural Hazards - In 2008, Wenchuan earthquake shook Sichuan Province in China. The questions of how to value the economic loss that would result if a catastrophe were to occur in Capital Beijing...  相似文献   

Controls on the height and spacing of eolian ripples and transverse dunes: A numerical modeling investigation     

Jon D. Pelletier   《Geomorphology》2009,105(3-4):322-333

Ripples and transverse dunes in areas of abundant sand supply increase in height and spacing as a function of time, grain size, and excess shear velocity. How and why each of these factors influence ripple and transverse dune size, however, is not precisely known. In this paper, the controls on the height and spacing of ripples and transverse dunes in areas of abundant sand supply are investigated using a numerical model for the formation of eolian bedforms from an initially flat surface. This bedform evolution model combines the basic elements of Werner's [Werner, B.T., 1995. Eolian dunes: Computer simulations and attractor interpretation. Geology 23, 1107–1110.] cellular automaton model of dune formation with a model for boundary layer flow over complex topography. Particular attention is paid to the relationship between bed shear stress and slope on the windward (stoss) side of evolving bedforms. Nonlinear boundary layer model results indicate that bed shear stresses on stoss slopes increase with increasing slope angle up to approximately 20°, then decrease with increasing slope angle as backpressure effects become limiting. In the bedform evolution model, the linear boundary layer flow model of Jackson and Hunt [Jackson, P.S., Hunt, J.C.R., 1975. Turbulent wind flow over a low hill. Quarterly Journal of the Royal Meteorological Society 101, 929–955.], generalized to 3D, is modified to include the nonlinear relationship between bed shear stress and slope. Bed shear stresses predicted by the modified Jackson and Hunt flow model are then used to predict rates of erosion and deposition iteratively through time within a mass-conservative framework similar to Werner [Werner, B.T., 1995. Eolian dunes: Computer simulations and attractor interpretation. Geology 23, 1107–1110.]. Beginning with a flat bed, the model forms ripples that grow in height and spacing until a dynamic steady-state condition is achieved in which bedforms migrate downwind without further growth. The steady-state ripple spacing predicted by this model is approximately 3000 times greater than the aerodynamic roughness length of the initially flat surface, which is a function of grain size and excess shear velocity. Once steady-state ripples form, they become the dominant roughness element of the surface. The increase in roughness associated with ripple formation triggers the same bedform instability that created ripples, causing dunes to form at a larger scale. In this way, the numerical model of this paper suggests that ripples and dunes are genetically linked. Transverse dunes in this model have a steady-state height and spacing that is controlled by the effective roughness length of the rippled surface, which is shown to be on the order of 500 times greater than the original roughness length, but varies significantly with the details of ripple morphology. The model predictions for ripple and dune spacing and their controlling variables are consistent with field measurements from the published literature. The model of this paper provides a preliminary process-based understanding of the granulometric control of ripples and dunes in areas of abundant sand supply and unidirectional prevailing winds, and it argues for a genetic linkage between ripples and dunes via a scaling relationship between eolian bedform size and the aerodynamic roughness length.  相似文献   

Potential link between exposure to fungicides chlorothalonil and mancozeb and haemic neoplasia development in the soft-shell clam Mya arenaria: A laboratory experiment     

Julie Pariseau  Richard Saint-Louis  Maryse Delaporte  Mohammed Abo El Khair  Réjean Tremblay  Emilien Pelletier 《Marine pollution bulletin》2009,58(4):503-514

The aetiology of haemic neoplasia (HN) is unknown, so far but many causative factors are suggested such as viral, pollution and genetics. The aim of this study was to determine if, under chronic exposure, two major pesticides (chlorothalonil and mancozeb) which are used in potato production could induce HN in soft-shell clams (Mya arenaria). Short-term experiments with acute exposure were also performed. Clams were collected from an epizootic site (North River, PEI) and from a site free of the disease (Magdalen Islands, Quebec). The tetraploid level of haemocytes was assessed by flow cytometry for each clam to determine the HN status. The bioaccumulation of pesticides in tissues was quantified by gas chromatography/mass spectrometry (GC/MS) for chlorothalonil while mancozeb and manganese were quantified by inductively coupled plasma-mass spectrometer (ICP/MS). Long term exposure to fungicide Bravo 500^® did not induce high tetraploid levels on negative calm from North River and the analysis of the digestive gland and the mantle did not reveal any detectable level of chlorothalonil. In the Manzate 200 DF^®, some clams revealed high level of tetraploid cells but no difference were observed between the treatments and the control. The analysis of the digestive gland and the mantle for manganese did not highlight any significant difference in tissue concentration (p = 0.05). For the acute exposure, chlorothalonil analysis showed that the active ingredient is distributed between four chlorinated compounds: 99.5% for chlorothalonil isomers, 0.4% for pentachlorothalonil and 0.1% for trichlorothalonil isomers. For a 72 h experiment, the accumulation was within 4 h; the higher tissue concentration of chlorothalonil was 59.2 μg g⁻¹ in the mantle after 48 h, following by a decrease to an undetectable level at the end. For the manganese, the accumulation was detected after 4 h; the higher tissue concentration was 48.8 μg g⁻¹ in the mantle after 24 h and, over the following 48 h, the accumulation decreased until the end of the trial. Based on the data, the accumulation of these fungicides seems to be transitory. Chlorothalonil and mancozeb are both oxidative-stress promoters and could have induced cell dysfunction while in the tissue. Study on the effect of these fungicides on the p53 protein system is an example of strategy that would provide information on cellular events promoting neoplasia.  相似文献   

In vivo formation of (+)-anti-benzo[a]pyrene diol-epoxide-plasma albumin adducts in fish.     

J Padrós  E Pelletier 《Marine environmental research》2000,50(1-5):347-351

Benzo[a]pyrene (BaP), a procarcinogenic polycyclic aromatic hydrocarbon (PAH), is bioactivated to BaP diol-epoxides (BPDEs) that can form adducts with DNA and blood proteins. We report here for the first time the in vivo formation of adducts between BPDE and plasma albumin (Alb) from two fish species experimentally exposed to BaP. Brook trout (Salvelinus fontinalis) received either a single i.p. dose (10 mg/kg) or two separate i.p. doses (25 mg/kg; 7 days apart) of BaP, and blood was collected 2 (single exposure) or 3 (multiple exposure) days post-treatment. Arctic charr (Salvelinus alpinus) received 10 i.p. doses (3 mg/kg; a single dose every 6 days), and blood was collected 2 days after the second, sixth, and 10th injections. BPDE-Alb adducts were measured by an improved HPLC/fluorescence method developed to detect and quantify BaP-tetrols released after acid hydrolysis of adducted Alb. HPLC/fluorescence chromatograms of Alb from BaP-treated fish revealed only BaP-tetrol I-1, thus indicating the formation of adducts exclusively via the (+)-anti-BPDE metabolite. Levels of (+)-anti-BPDE-Alb adduct ranged from 0.68 to 19.6 ng of tetrol I-1 per gram of Alb. Notably, adduct level was not related to BaP dose and there was no accumulation of adducts with repeated exposure, which may indicate a very short half-life (< 2 days) of plasma Alb in fish. The data suggest that BPDE-Alb adducts in fish could be useful as a non-destructive biomarker of recent exposure to bioactivated BaP.  相似文献   

Recent climatic trends and linkages to river discharge in Central Vietnam   总被引：1，自引：0，他引：1       下载免费PDF全文

Maxime Souvignet  Patrick Laux  Jim Freer  Hannah Cloke  Dang Quang Thinh  Tran Thuc  Johannes Cullmann  Alexandra Nauditt  Wolfgang‐Albert Flügel  Harald Kunstmann  Lars Ribbe 《水文研究》2014,28(4):1587-1601

In this study, change in rainfall, temperature and river discharge are analysed over the last three decades in Central Vietnam. Trends and rainfall indices are evaluated using non‐parametric tests at different temporal levels. To overcome the sparse locally available network, the high resolution APHRODITE gridded dataset is used in addition to the existing rain gauges. Finally, existing linkages between discharge changes and trends in rainfall and temperature are explored. Results are indicative of an intensification of rainfall (+15%/decade), with more extreme and longer events. A significant increase in winter rainfall and a decrease in consecutive dry days provides strong evidence for a lengthening wet season in Central Vietnam. In addition, trends based on APHRODITE suggest a strong orographic signal in winter and annual trends. These results underline the local variability in the impacts of climatic change at the global scale. Consequently, it is important that change detection investigations are conducted at the local scale. A very weak signal is detected in the trend of minimum temperature (+0.2°C/decade). River discharge trends show an increase in mean discharge (31 to 35%/decade) over the last decades. Between 54 and 74% of this increase is explained by the increase in precipitation. The maximum discharge also responds significantly to precipitation changes leading to a lengthened wet season and an increase in extreme rainfall events. Such trends can be linked with a likely increase in floods in Central Vietnam, which is important for future adaptation planning and management and flood preparedness in the region. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

On the transition from strombolian to fountaining activity: a thermal energy-based driver     

Maxime Bombrun  Letizia Spampinato  Andrew Harris  Vincent Barra  Tommaso Caltabiano 《Bulletin of Volcanology》2016,78(2):15

  相似文献   

Structural Setting of the Neoarchean Terrains in the Commonwealth Bay Area (143-145°E), Terre Adélie Craton, East Antarctica     

R-P. Mnot  A. Pêcher  Y. Rolland  J-J. Peucat  A. Pelletier  G. Duclaux  S. Guillot 《Gondwana Research》2005,8(1):1-9

Geological maps of East Commonwealth Bay Unit (ECB), (Terre Adélie and Georges V Land, Antarctica) are presented with a summary of the main structural and metamorphic data for the region. The ECB unit was developed during Neoarchean_Paleoproterozoic event (at 2.5-2.42 Ga), with (i) granulite metamorphism at 9±1.5 kbar and 800±50°C in the lower crust section and amphibolite metamorphism (P=5 kbar, T=750°C) at the upper crustal levels; (ii) the lower crustal granulites were uplifted, and suffered local partial melting and retrogression to the amphibolite facies at 550±50°C_5 kbar. Granulites were extruded in the core of a crustal-scale anticlinal fold, but retrogressed only on the rims of the anticline. Crustal-scale folding, along with other structural features resulted from intense NE-SW shortening that prevailed during the Neoarchean orogenic cycle. Strike-slip and extensional motions were only minor components in that process; (iii) top-to-the-East thrusting and nappe piling had (at least locally) occurred under lower amphibolite to greenschist facies conditions. Finally, it seems that (iv) the Paleoproterozoic 1.7 Ga structural imprint may have only affected the rims of the Archean units. The tectonic context observed in the 1.7 Ga Cape Hunter phyllites features mainly an E-W shortening component and vertical extrusion. The eastern (Mertz) and western (Port Martin) parts of the Archean block were reactivated by localized dextral shearing.  相似文献