119 research outputs found
Le haut marais de lâIsle-aux-Grues : un exemple dâexploitation et de dĂ©veloppement durables
Synonymes de richesses animales et vĂ©gĂ©tales, les marais de lâestuaire du fleuve Saint-Laurent ont Ă©tĂ© exploitĂ©s depuis longtemps, dâabord par les AmĂ©rindiens puis par les colons europĂ©ens. Toutefois, lâindustrialisation a entraĂźnĂ© leur destruction : plus de la moitiĂ© des milieux humides de lâestuaire du Saint-Laurent a disparu. Dans lâoptique du dĂ©veloppement durable, cet article a pour but dâexplorer la relation gĂ©ohistorique entre sociĂ©tĂ© et environnement sur le haut marais de lâIsle-aux-Grues, une relation qui a pris appui sur les limites et les processus naturels de lâĂ©cosystĂšme, Ă la diffĂ©rence de ce quâon observe dans plusieurs autres environnements humides de lâestuaire. Depuis quatre siĂšcles, les humains ont dĂ©veloppĂ© un rapport durable avec la nature, en faisant du haut marais de lâIsle-aux-Grues un lieu de chasse, de pĂȘche, de rĂ©colte du foin de mer et de loisir.Synonymous with faunal and floral abundance, the marshes of the St. Lawrence Estuary have been exploited for centuries, first by Amerindians, then by European settlers. Industrialisation, however, brought about their destruction : more than half of the estuaryâs wetlands have disappeared. Within the context of sustainable development, this article explores the geohistorical relationship between society and the environment in the high marsh area of Isle-aux-Grues, a relationship that respects the natural processes and limits of this ecosystem, unlike what can be observed in many other wetlands in the estuary. Over the past four centuries, humans have developed a sustainable relationship with nature by using the high marsh area of Isle-aux-Grues for hunting, fishing, harvesting marsh hay and leisure activities
Factors affecting river turbidity in a degrading permafrost environment : the Tasiapik River, Umiujaq (Nunavik)
This study focuses on spatiotemporal changes in water turbidity in relation to permafrost to document the impact of meteorological conditions and water flow on hydro-sedimentary processes in northern regions. Starting in June of 2019, water turbidity data were collected at six sites along the Tasiapik River (Nunavik). A statistical analysis was completed based on records of water turbidity, precipitation, water flow, and air temperature. Our results show a significant correlation between air temperatures and turbidity, with a correlation of up to r = 0.59. These correlations depend on the location of the site along the river and the time of the study period (JuneâOctober 2019). The flow rate was the primary factor that caused variations in the turbidity of the Tasiapik River. Our results showed that following an increase in flow rate, there was an almost simultaneous increase in turbidity due to erosion of the banks. The duration and intensity of precipitation events are also important factors affecting the process of sediment transport. Even though meteorological conditions play an important role in turbidity variation, other characteristics of the site such as the topography and the existence of thermokarst lakes are additional factors that influence the dynamics of sediment transport in the Tasiapik River.Les travaux menĂ©s en Arctique et Subarctique dĂ©montrent une accĂ©lĂ©ration de la dĂ©gradation du pergĂ©lisol durant les derniĂšres dĂ©cennies, provoquant des tassements importants du sol et par le fait mĂȘme, un accroissement du fluage dâeau chargĂ©e de sĂ©diments vers les lacs et les riviĂšres. Cette Ă©tude vise Ă mieux comprendre la variation spatio-temporelle de la turbiditĂ© fluviale en contexte pĂ©riglaciaire dans le but de faire avancer les connaissances sur les impacts des conditions mĂ©tĂ©orologiques et du dĂ©bit sur les processus hydrosĂ©dimentaires des rĂ©gions nordiques. Des donnĂ©es de turbiditĂ© de lâeau de la riviĂšre Tasiapik, situĂ©e Ă 5 km Ă lâest du village dâUmiujaq (Nunavik), ont Ă©tĂ© enregistrĂ©es de juin Ă octobre 2019 dans six sites distincts. Des analyses statistiques rĂ©alisĂ©es sur ces enregistrements indiquent quâil existe une corrĂ©lation significative (r = 0,59) entre les tempĂ©ratures de lâair et la turbiditĂ© de la riviĂšre. Ces relations sont plus ou moins importantes selon
lâemplacement du site le long de la riviĂšre et selon le moment de la pĂ©riode dâĂ©tude. Le dĂ©bit Ă©tait le principal facteur Ă lâorigine des variations de la turbiditĂ© de la riviĂšre Tasiapik. Nos rĂ©sultats ont montrĂ© quâĂ la suite dâune augmentation du dĂ©bit, il y a eu une augmentation presque simultanĂ©e de la turbiditĂ© due Ă lâĂ©rosion des berges et de la quantitĂ© des sĂ©diments en suspension. La durĂ©e et lâintensitĂ© des prĂ©cipitations sont Ă©galement des facteurs importants ayant fait varier la turbiditĂ© de la riviĂšre. Bien que les conditions mĂ©tĂ©orologiques jouent un rĂŽle important dans la variation de la turbiditĂ©, il sâest avĂ©rĂ© que les caractĂ©ristiques du site telles que la topographie et la prĂ©sence de lacs thermokarstiques sont des facteurs importants dans la dynamique du transport sĂ©dimentaire de la riviĂšre Tasiapik
Temporal variations in English Populations of a forest insect pest, the green spruce aphid (Elatobium abietinum), associated with the North Atlantic Oscillation and global warming
Based on an exceptionally long modern ecological dataset (41 years), it has been possible to show that warm weather in England associated with a positive North Atlantic Oscillation (NAO) index causes the spring migration of the green spruce aphid (Elatobium abietinum), a pest species of spruce trees (Picea) to start earlier, continue for longer and contain more aphids. An upward trend in the NAO index during the period 1966-2006 is associated with an increasing population size of E. abietinum. It is important to understand the mechanisms behind the population fluctuations, because this aphid causes considerable damage to Picea plantations. Present day weather associated fluctuations in forest insect pests may be useful analogues in understanding past pest outbreaks in forests
Abrupt climate change as an important agent of ecological change in the Northeast U.S. throughout the past 15,000 years
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Quaternary Science Reviews 28 (2009): 1693-1709, doi:10.1016/j.quascirev.2009.04.005.We use a series of tests to evaluate two competing hypotheses about the association of climate
and vegetation trends in the northeastern United States over the past 15 kyrs. First, that abrupt
climate changes on the scale of centuries had little influence on long-term vegetation trends,
and second, that abrupt climate changes interacted with slower climate trends to determine the
regional sequence of vegetation phases. Our results support the second. Large dissimilarity
between temporally-close fossil pollen samples indicates large vegetation changes within 500
years across >4° of latitude at ca. 13.25-12.75, 12.0-11.5, 10.5, 8.25, and 5.25 ka. The evidence of
vegetation change coincides with independent isotopic and sedimentary indicators of rapid
shifts in temperature and moisture balance. In several cases, abrupt changes reversed long-term
vegetation trends, such as when spruce (Picea) and pine (Pinus) pollen percentages rapidly
declined to the north and increased to the south at ca. 13.25-12.75 and 8.25 ka respectively.
Abrupt events accelerated other longâterm trends, such as a regional increase in beech (Fagus)
pollen percentages at 8.5-8.0 ka. The regional hemlock (Tsuga) decline at ca. 5.25 ka is unique
among the abrupt events, and may have been induced by high climatic variability (i.e., repeated
severe droughts from 5.7-2.0 ka); autoregressive ecological and evolutionary processes could
have maintained low hemlock abundance until ca. 2.0 ka. Delayed increases in chestnut
(Castanea) pollen abundance after 5.8 and 2.5 ka also illustrate the potential for multi-century
climate variability to influence speciesâ recruitment as well as mortality. Future climate changes
will probably also rapidly initiate persistent vegetation change, particularly by acting as broad,
regional-scale disturbances.This work was supported by NSF grants to B. Shuman (EARâ0602408; DEBâ0816731) and J.
Donnelly (EARâ0602380)
Oxygen dynamics in permafrost thaw lakes: Anaerobic bioreactors in the Canadian subarctic
Permafrost thaw lakes occur in high abundance across the subarctic landscape but little is known about their limnological dynamics. This study was undertaken to evaluate the hourly, seasonal, and depth variations in oxygen concentration in three thaw lakes in northern Quebec, Canada, across contrasting permafrost regimes (isolated, sporadic, and discontinuous). All lakes were well stratified in summer despite their shallow depths (2.7-4.0m), with hypoxic or anoxic bottom waters. Continuous automated measurements in each of the lakes showed a period of water column oxygenation over several weeks in fall followed by bottom-water anoxia soon after ice-up. Anoxic conditions extended to shallower depths (1m) over the course of winter, beginning 18-137 d after ice formation, depending on the lake. Full water column anoxia extended over 33-75% of the annual record. There was a brief period of incomplete spring mixing with partial or no reoxygenation of the bottom waters in each lake. Conductivity measurements showed the build-up of solutes in the bottom waters, and the resultant density increase contributed to the resistance to full mixing in spring. These observations indicate the prevalence of stratified conditions throughout most of the year and underscore the importance of the fall mixing period for gas exchange with the atmosphere. Given the long duration of anoxia, subarctic thaw lakes represent an ideal environment for anaerobic processes such as methane production. The intermittent oxygenation also favors intense methanotrophy and aerobic bacterial decomposition processes
High methylmercury in Arctic and subarctic ponds is related to nutrient levels in the warming eastern Canadian Arctic
Permafrost thaw ponds are ubiquitous in the eastern
Canadian Arctic, yet little information exists on their potential as
sources of methylmercury (MeHg) to freshwaters. They are
microbially active and conducive to methylation of inorganic
mercury, and are also affected by Arctic warming. This multiyear
study investigated thaw ponds in a discontinuous permafrost region
in the Subarctic taiga (Kuujjuarapik-Whapmagoostui, QC) and a
continuous permafrost region in the Arctic tundra (Bylot Island,
NU). MeHg concentrations in thaw ponds were well above levels
measured in most freshwater ecosystems in the Canadian Arctic
(>0.1 ng Lâ1). On Bylot, ice-wedge trough ponds showed
significantly higher MeHg (0.3â2.2 ng Lâ1) than polygonal
ponds (0.1â0.3 ng Lâ1) or lakes (<0.1 ng Lâ1). High MeHg was
measured in the bottom waters of Subarctic thaw ponds near
Kuujjuarapik (0.1â3.1 ng Lâ1). High water MeHg concentrations in thaw ponds were strongly correlated with variables
associated with high inputs of organic matter (DOC, a320, Fe), nutrients (TP, TN), and microbial activity (dissolved CO2 and
CH4). Thawing permafrost due to Arctic warming will continue to release nutrients and organic carbon into these systems and
increase ponding in some regions, likely stimulating higher water concentrations of MeHg. Greater hydrological connectivity
from permafrost thawing may potentially increase transport of MeHg from thaw ponds to neighboring aquatic ecosystems
Landscape-gradient assessment of thermokarst lake hydrology using water isotope tracers
Thermokarst lakes are widespread in arctic and subarctic regions. In subarctic
Québec (Nunavik), they have grown in number and size since the mid-20th century.
Recent studies have identified that these lakes are important sources of greenhouse
gases. This is mainly due to the supply of catchment-derived dissolved organic carbon
that generates anoxic conditions leading to methane production. To assess the potential
role of climate-driven changes in hydrological processes to influence greenhouse-gas
emissions, we utilized water isotope tracers to characterize the water balance of
thermokarst lakes in Nunavik during three consecutive mid- to late summer seasons
(2012-2014). Lake distribution stretches from shrub-tundra overlying discontinuous
permafrost in the north to spruce-lichen woodland with sporadic permafrost in the south.
Calculation of lake-specific input water isotope compositions (I) and lake-specific
evaporation-to-inflow (E/I) ratios based on an isotope-mass balance model reveal a
narrow hydrological gradient regardless of diversity in regional landscape
characteristics. Nearly all lakes sampled were predominantly fed by rainfall and/or
permafrost meltwater, which suppressed the effects of evaporative loss. Only a few
lakes in one of the southern sampling locations, which overly highly degraded sporadic
permafrost terrain, appear to be susceptible to evaporative lake-level drawdown. We
attribute this lake hydrological resiliency to the strong maritime climate in coastal regions
of Nunavik. Predicted climate-driven increases in precipitation and permafrost
degradation will likely contribute to persistence and expansion of thermokarst lakes
throughout the region. If coupled with an increase in terrestrial carbon inputs to
thermokarst lakes from surface runoff, conditions favorable for mineralization and
emission of methane, these water bodies may become even more important sources of
greenhouse gases
Reading between the rings: climatic and biotic controls of shrub growth and expansion in the tundra biome
The tundra biome has undergone dramatic vegetation shifts in recent decades, which
have been partly attributed to climate warming. Shrub species in particular are
expanding widely throughout the Pan-Arctic region, and are involved in complex
vegetation-atmosphere interactions that have important implications for the global
energy balance and carbon budget. However, projections of vegetation change and
associated feedbacks are complicated by the high variability in the sensitivity of shrub
growth to temperature among sites and species. A mechanistic understanding of the
individual-to-regional controls of climate sensitivity is therefore needed to accurately
predict future vegetation change at the biome scale. This thesis quantifies the
influence of environmental and ecological factors, and especially of plant-plant
interactions, on the growth response of Arctic shrub communities to climate change.
Climate change in the Arctic has resulted in warmer, but also longer growing seasons
in many locations due to earlier snowmelt. These two factors are often treated as one
single control of plant growth, but with scarce records of green-up and senescence
dates for the Arctic, few studies have measured the sensitivity of shrub growth to
changes in growing season length. Using radial growth time series from over 300
shrubs collected at four sites of contrasting climatic regimes and greening trajectories
in Northern Canada, I measured the sensitivity of shrub growth to summer
temperature and satellite-derived growing season length. I found that growing season
length and summer temperature were decoupled within sites and had inconsistent
effects on growth across the four sites. My findings indicate that longer and warmer
growing seasons do not necessarily act as combined drivers of vegetation change
across the biome. My research also demonstrated that growth at the root collar of
shrubs is more climate sensitive than stem growth, possibly indicating differential
internal resource allocation strategies, and highlighting the importance of
standardised protocols when comparing dendroecological data across multiple sites.
Individual and species traits are thought to play an important role in the response of
tundra vegetation to climate change. Taller shrub species have been shown to be
more climate-sensitive than dwarf shrubs, but whether this relationship holds at the
individual level is unknown. I tested whether plant size, as a proxy for competitive
ability, explained variation in the climate sensitivity of shrub growth using 1085
individual size and growth-ring records from 16 species at 18 sites across the tundra
biome. I did not find evidence that taller shrubs were more climate sensitive, and found
that height became a progressively poorer predictor of other growth dimensions at
higher latitudes. This suggests that predictions of functional and structural change
based on allometric equations from boreal or sub-Arctic populations may not be valid
for the tundra biome as a whole.
Plant-plant interactions are a strong driver of community dynamics. With increasing
shrub densities in the circumpolar region, competition could have an increasingly
important influence on shrub growth, potentially limiting climate-driven expansion. I
found that competition with trees might slow down shrub expansion in the boreal forest
biome, as the climate sensitivity of shrub growth was much lower in a boreal forest in
southwest Yukon compared to shrubs growing in the alpine tundra in the same region.
However, my findings did not indicate a strong control of shrub-shrub competition on
growth. A canopy removal experiment did not reveal any difference in the growth rate
of shrubs having experienced a decrease in aboveground competition compared to
shrubs growing in intact shrub patches. Additionally, shrubs experiencing more
competition were generally as climate sensitive as those with fewer or more distant
neighbours, as I demonstrated through spatial analysis at four sites across the
Canadian Arctic. However, their spatial arrangement, with positive size-distance
relationships between pairs of neighbours, suggested that competition does play a
role in the life history of these shrubs, especially at more productive sites. Finally, I
found evidence of physical and chemical interference of ground vegetation on the
germination of deciduous shrub seeds, indicating that interactions with other plant
functional groups may control rates of shrub expansion.
Shrub expansion at the plot to landscape scale has been heavily documented over
multiple decades through several lines of evidence including long-term monitoring,
remote sensing, and experimental studies. The increase in shrub biomass in the
tundra has high certainty both in detection and in attribution to climate warming.
However, my thesis highlights the complexity and variability of growth responses
when using radial growth as an indicator of climate sensitivity. I detected this variability
at multiple scales, from plant parts within an individual showing inconsistent climatic
signals, to site-scale sensitivity responding to different facets of global change. I did
not find strong or consistent influences of biotic and abiotic controls on the growth
responses of tundra shrubs; however, these relationships may change over time as
shrub densities continue to increase and exacerbate resource limitations. With 80%
of tundra biomass potentially located below ground, understanding whole-plant and
community-level responses to climate will be critical to improve projections of tundra
plant community responses to global change. Understanding the different drivers of
primary and secondary growth will be key to using estimates of climate sensitivity
derived from growth-ring records to project biomass change and associated
feedbacks across the tundra biome
Structure des peuplements, rĂ©gimes de perturbation et dynamiques de succession dans les forĂȘts borĂ©ales eurasiennes : une revue basĂ©e sur des travaux russes
VEYRET, Yvette et VIGNEAU, Jean-Pierre, dir. (2002) Géographie physique. Milieux et environnement dans le systÚme terre. Paris, Armand Collin (Coll. « U- Géographie », 368 p. (ISBN 2-200-25236-6)
- âŠ