Holocene vegetation dynamics and hydrological variability in forested peatlands of the Clay Belt,eastern Canada,reconstructed using a palaeoecological approach     

Gabriel Magnan  loise Le Stum‐Boivin  Michelle Garneau  Pierre Grondin  Nicole Fenton  Yves Bergeron 《Boreas: An International Journal of Quaternary Research》2019,48(1):131-146

Forested peatlands are widespread in boreal regions of Canada, and these ecosystems, which are major terrestrial carbon sinks, are undergoing significant transformations linked to climate change, fires and human activities. This study targets millennial‐scale vegetation dynamics and related hydrological variability in forested peatlands of the Clay Belt south of James Bay, eastern Canada, using palaeoecological data. Changes in peatland vegetation communities were reconstructed using plant macrofossil analyses, and variations in water‐table depths were inferred using testate amoeba analyses. High‐resolution analyses of macroscopic charcoal >0.5 mm were used to reconstruct local fire history. Our data showed two successional pathways towards the development of present‐day forested peatlands influenced by autogenic processes such as vertical peat growth and related drying, and allogenic factors such as the occurrence of local fires. The oldest documented peatland initiated in a wet rich fen around 8000 cal. a BP shortly after land emergence and transformed into a drier forested bog rapidly after peat inception that persisted over millennia. In the second site, peat started to accumulate from ~5200 cal. a BP over a mesic coniferous forest that shifted into a wet forested peatland following a fire that partially consumed the organic layer ~4600 cal. a BP. The charcoal records show that fires rarely occurred in these peatlands, but they have favoured the process of forest paludification and influenced successional trajectories over millennia. The macrofossil data suggest that Picea mariana (black spruce) persisted on the peatlands throughout their development, although there were periods of more open canopy due to local fires in some cases. This study brings new understanding on the natural variability of boreal forested peatlands which may help predict their response to future changes in climate, fire regimes and anthropogenic disturbances.  相似文献   

Extension at the coast of the Makran subduction zone (Iran)     

Raphaël Normand  Guy Simpson  Abbas Bahroudi 《地学学报》2019,31(6):503-510

In the Makran subduction zone, earthquake focal mechanisms and geodetic data indicate that the deforming prism currently experiences N–S compression. However, palaeostress inversions performed on normal faults observed along the coast reveal local stress components consistent with N‐S extension. Previously proposed mechanisms such as gravitational collapse are not favoured by N–S compression and surface uplift. We propose that the observed kinematics result from transient stress reversals following large earthquakes. During the interseismic period (now), the region experiences N–S compression. However, following a large reverse rupture on the subduction interface, stresses in the inner wedge relax, enabling a brief period of extensional faulting before a compressive stress state is re‐established. This mechanism, also observed in other subduction zones, requires low overall stresses in the upper plate and that the margin ruptures in large megathrust earthquakes that result in nearly complete stress drops.  相似文献   

Flood events and flood risk assessment in relation to climate and land-use changes: Saint-François River,southern Québec,Canada     

C. Ouellet  F. Normand 《水文科学杂志》2013,58(2):313-325

Abstract

In the current context of climatic variability, it is important to quantify the impact on the environment. This study deals with an analysis of climatic data and land-use changes in terms of the impacts on flood recurrence based on multisource data. The study area covers the mouth of the Saint-François River (southern Québec, Canada), where spring floods and ice jams are a recurring problem. The flood frequency analysis shows an increase in flooding over recent decades, attributable to an increase in winter temperatures that has the effect of causing ice jams earlier in the year. Regarding land-use changes, a small decrease in agricultural surface areas is observed, from 53% to 39%, along with increases in forest and urban surface areas from 27% to 38% (forest) and 3% to 5% (urban) between 1928 and 2005. In a context of continuing climate warming, more pronounced inter-annual variations are to be expected along with a higher incidence of flooding.

Editor Z.W. Kundzewicz

Citation Ouellet, C., Saint-Laurent, D. and Normand, F., 2012. Flood events and flood risk assessment in relation to climate and land-use changes: Saint-François River, southern Québec, Canada. Hydrological Sciences Journal, 57 (2), 313–325.  相似文献   

The discovery of a massive supercluster at  z= 0.9  in the UKIDSS Deep eXtragalactic Survey     

A. M. Swinbank  A. C. Edge  Ian Smail  J. P. Stott  M. Bremer  Y. Sato  C. van Breukelen  M. Jarvis  I. Waddington  L. Clewley  J. Bergeron  G. Cotter  S. Dye  J. E. Geach  E. Gonzalez-Solares  P. Hirst  R. J. Ivison  S. Rawlings  C. Simpson  G. P. Smith  A. Verma  T. Yamada 《Monthly notices of the Royal Astronomical Society》2007,379(4):1343-1351

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Major postglacial summer temperature changes in the central coniferous boreal forest of Quebec (Canada) inferred using chironomid assemblages          下载免费PDF全文

Lisa Bajolle  Isabelle Larocque‐Tobler  Emmanuel Gandouin  Martin Lavoie  Yves Bergeron  Adam A. Ali 《第四纪科学杂志》2018,33(4):409-420

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Thermal Convection in Finite Prandtl Number Fluids at High Rayleigh Number     

Catherine A. Hier  Stephen Y. Bergeron  David A. Yuen  Erik O. Sevre  John M. Boggs 《Visual Geosciences》2001,6(3):1-4

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Hydrochemical Facies in a Tertiary Basin in the Milligan Canyon Area, Southwest Montana     

Noel C. Krothe  Marcel P. Bergeron 《Ground water》1981,19(4):392-399

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Identifying the potential loss of monitoring wells using an uncertainty analysis     

Freedman VL  Waichler SR  Cole CR  Vermeul VR  Bergeron MP 《Ground water》2005,43(6):916-925

From the mid-1940s through the 1980s, large volumes of waste water were discharged at the Hanford Site in southeastern Washington State, causing a large-scale rise (>20 m) in the water table. When waste water discharges ceased in 1988, ground water mounds began to dissipate. This caused a large number of wells to go dry and has made it difficult to monitor contaminant plume migration. To identify monitoring wells that will need replacement, a methodology has been developed using a first-order uncertainty analysis with UCODE, a nonlinear parameter estimation code. Using a three-dimensional, finite-element ground water flow code, key parameters were identified by calibrating to historical hydraulic head data. Results from the calibration period were then used to check model predictions by comparing monitoring wells' wet/dry status with field data. This status was analyzed using a methodology that incorporated the 0.3 cumulative probability derived from the confidence and prediction intervals. For comparison, a nonphysically based trend model was also used as a predictor of wells' wet/dry status. Although the numerical model outperformed the trend model, for both models, the central value of the intervals was a better predictor of a wet well status. The prediction interval, however, was more successful at identifying dry wells. Predictions made through the year 2048 indicated that 46% of the wells in the monitoring well network are likely to go dry in areas near the river and where the ground water mound is dissipating.  相似文献   

Influence of a multiplicative noise on the threshold of helical dynamo     

Christiane Normand 《地球物理与天体物理流体动力学》2013,107(1):90-108

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Evaluating the persistence of post‐fire residual patches in the eastern Canadian boreal mixedwood forest          下载免费PDF全文

Samira Ouarmim  Adam A. Ali  Hugo Asselin  Christelle Hély  Yves Bergeron 《Boreas: An International Journal of Quaternary Research》2015,44(1):230-239

In boreal forest ecosystems, wildfire severity (i.e. the extent of fire‐related tree mortality) is affected by environmental conditions and fire intensity. A burned area usually includes tree patches that partially or entirely escaped fire, called ‘residual patches’. Although the occurrence of residual patches has been extensively documented, their persistence through time, and thus their capacity to escape several consecutive fires, has not yet been investigated. Macroscopic charcoal particles embedded in organic soils were used to reconstruct the fire history of 13 residual patches of the eastern Canadian boreal mixedwood forest. Our results display the existence of two types of residual patches: (i) patches that only escaped fire by chance, maybe because of local site or meteorological conditions unsuitable for fire spread (random patches), and (ii) patches with lower fire susceptibility, also called ‘fire refuges’ that escaped at least two consecutive fires, probably because of particular site characteristics. Fire refuges can escape fire for more than 500 years, up to several thousand years, and probably burn only during exceptionally severe fire events. Special conservation efforts could target fire refuges owing to their old age, long ecological continuity and potential specific biological diversity associated to different microhabitats.  相似文献