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Freshwater lakes in the Canadian Maritime provinces have been detrimentally influenced by multiple, often synergistic, anthropogenically-sourced environmental stressors. These include surface-water acidification (and a subsequent decrease in calcium loading to lakes); increased nutrient inputs; watershed development; invasive species; and climate change. While detailed studies of these stressors are often hindered by a lack of predisturbance monitoring information; in many cases, these missing data can be determined using paleolimnological techniques, along with inferences on the full extent of environmental change (and natural variability), the timing of changes, and linkages to probable causes for change. As freshwater resources are important for fisheries, agriculture, municipal drinking water, and recreational activities, among others, understanding long-term ecological changes in response to anthropogenic stressors is critical. To assess the impacts of the major water-quality issues facing freshwater resources in this ecologically significant region, a large number of paleolimnological studies have recently been conducted in Nova Scotia and southern New Brunswick. These studies showed that several lakes in southwestern Nova Scotia, especially those in Kejimkujik National Park, have undergone surface-water acidification (mean decline of 0.5 pH units) in response to local-source S[O.sub.2] emissions and the long-range transport of airborne pollutants. There has been no measureable chemical or biological recovery since emission restrictions were enacted. Lakewater calcium (Ca) decline, a recently recognized environmental stressor that is inextricably linked to acidification, has negatively affected the keystone zooplankter Daphnia in at least two lakes in Nova Scotia (and likely more), with critical implications for aquatic food webs. A consistent pattern of increasing planktonic diatoms and scaled chrysophytes was observed in lakes across Nova Scotia and New Brunswick, suggesting that the strength and duration of lake thermal stratification has increased since pre-industrial times in response to warming temperatures (~1.5 °C since 1870). These include three lakes near Bridgewater, Nova Scotia, that are among the last known habitat for critically endangered Atlantic whitefish (Coregonus huntsmani). Overall, these studies suggest that aquatic ecosystems in the Maritime Provinces are being affected by multiple anthropogenic stressors and paleolimnology can be effective for inferring the ecological implications of these stressors. Key words: acidification, climate change, eutrophication, New Brunswick, Nova Scotia, paleolimnology. Les lacs d'eau douce des provinces maritimes canadiennes ont ete influences de facon nefaste par de multiples agents stressants environnementaux souvent synergiques et de sources anthropogenes, incluant l'acidification de l'eau de surface (avec une diminution subsequente de la charge en calcium dans les lacs), les apports accrus en nutriment, le developpement des bassins versants, les especes envahissantes ainsi que le changement climatique. Alors que les etudes detaillees de ces agents stressants sont souvent compromises par une absence d'informations suivies on peut dans plusieurs cas determiner ces donnees manquantes en utilisant des techniques paleolimnologiques, avec des inferences sur la pleine etendue du changement environnemental (et la variabilite naturelle), les changements de l'incidence et la liaison avec les causes probables du changement. Comme les ressources en eau douce sont importantes pour les pecheries, l'agriculture, l'eau potable municipale, et les activites de recreation, parmi d'autres, la comprehension a long terme des changements ecologiques en reaction aux agents stressants anthropogenes devient critique. Afin d'evaluer les impacts de ces questions sur la qualite de l'eau menacant les ressources en eau douce dans cette region ecologique significative, on a conduit recemment un grand nombre d'etudes paleolimnologiques en Nouvelle-Ecosse et dans le sud du Nouveau-Brunswick. Ces etudes ont montre que plusieurs lacs du sud-ouest de la Nouvelle Ecosse, specialement ceux du parc national de Kejimkujik, ont subi une acidification des eaux de surface (diminution moyenne de 0.5 unites de pH) en reaction a des emissions locales de S[O.sub.2] et le transport a longue distance de polluants atmospheriques. On a observe aucune amelioration chimique ou biologique mesurable depuis les restrictions sur les emissions mises en ceuvre. Le declin en calcium (Ca) des lacs, un agent stressant environnemental recemment reconnu lie de facon inextricable a l'acidification, a negativement affecte le Daphnia, element cle du zooplancton, au moins dans deux lacs de Nouvelle-Ecosse (possiblement plus), avec des implications critiques pour la chaine alimentaire aquatique. On observe un patron congru dans l'augmentation des diatomees planctoniques et des chrysophytes ecailleuses dans des lacs sur l'ensemble de la Nouvelle Ecosse et du Nouveau Brunswick, suggerant que la force et la duree de la stratification thermique a augmente depuis la periode pre-industrielle en reaction au rechauffement des temperatures (~1.5°C depuis 1870). Ceci inclue trois lacs pres de Bridgewater en Nouvelle Ecosse, etant parmi les derniers habitats reconnus pour le coregone de l'Atlantique Coregone huntsmani), une espece menacee. Dans l'ensemble, ces etudes suggerent que les ecosystemes aquatiques des provinces maritimes sont affectes par de multiples agents stressants anthropogenes, et que la paleoclimatiologie peut etre efficace pour rendre compte des implications ecologiques de ces agents stressants. [Traduit par la Redaction] Mots-cles: acidification, changement climatique, eutrophication, Nouveau Brunswick, Nouvelle Ecosse, paleoclimatologie., Introduction Maintaining the ecological integrity of freshwater ecosystems is of critical importance globally, as deteriorating water quality is not only an environmental concern, but also has economic and social implications. [...]

This investigation provides evidence of biological recovery from acidification in an acid-impacted Adirondack (New York, USA) lake. Water chemistry measurements collected monthly since 1982 show that Big Moose Lake is undergoing chemical recovery from acid deposition. To assess possible biological recovery, changes in chrysophyte, diatom, and cladoceran assemblages are analyzed in a sediment core. Three questions are addressed: (i) is there a significant shift in species composition after the 1995 implementation of the US Acid Rain Program? (ii) Are post-1995 changes in species composition consistent with chemical recovery from acidification or, rather, other changing chemical/climatic factors? (iii) Are the species assemblages returning to their pre-acidification state? Post-1995 declines in the relative abundance of diatom and chrysophyte taxa with low pH-optima and increases in taxa with higher pH-optima indicate biological recovery from acidification. In contrast, the cladocera remain unresponsive to post-1995 increases in pH. No species group has returned to its pre-disturbance state and post-ca. 1995 increases in certain taxa (e.g., Synura echinulata) may be related to recent climate warming in the Adirondacks. Notre recherche apporte des preuves de la recuperation biologique de l'acidification dans un lac affecte par l'acidite dans les Adirondacks (New York, E.-U.). Des donnees de chimie de l'eau recoltees a chaque mois depuis 1982 montrent que le lac Big Moose connait un retablissement chimique des effets des precipitations acides. Afin d'evaluer la possibilite d'un retablissement biologique, nous avons analyse les changements dans les peuplements de chrysophytes, de diatomees et de cladoceres dans une carotte de sediments. Nous posons trois questions: (i) est-ce que la mise en vigueur du programme americain sur les pluies acides (U.S. Acid Rain Program) en 1995 a entraine un changement significatif dans la composition des especes? (ii) Les changements observes apres 1995 correspondent-ils au retablissement chimique apres l'acidification ou plutot a la modification d'autres facteurs chimiques/climatiques? (iii) Les associations d'especes retournent-elles a leur etat d'avant l'acidification? Le declin apres 1995 de l'abondance relative des taxons de diatomees et de chrysophytes a pH optimum bas et l'augmentation des taxons a pH optimum plus eleve indiquent un retablissement biologique de l'acidification. En revanche, les cladoceres ne repondent pas a l'augmentation de pH depuis 1995. Aucun des groupes d'especes n'a retrouve son etat d'avant la perturbation; les augmentations de certains taxons (en particulier, Synura echinulata) peuvent etre dues a un rechauffement climatique recent dans les Adirondacks. [Traduit par la Redaction], Introduction Acid deposition, a by-product of fossil fuel combustion, has severely impacted aquatic ecosystems across North America and Europe. Acidification (i.e., a decline in lake-water pH and acid neutralizing capacity) [...]

Pollen and diatom assemblages from well-dated sediment cores from three lakes forming a west-to-east transect across the boreal forest in northwest Ontario (Canada) were used to evaluate the timing and nature of the movement of the prairie-forest ecotone (PFE) across the Holocene. Changes in vegetation, temperature, and effective moisture were inferred from pollen and pollen-based transfer functions. Analyses indicated site-specific vegetational and climate changes across short spatial distances, with prolonged prairie-like conditions during the middle Holocene at the westernmost site. Increased reconstructed temperatures at this westernmost site occurred from ∼9000 to 3000 cal yr BP, alongside increases in diatom-inferred lake levels beginning at ∼6000 cal yr BP. The abundance of Quercus peaked concurrently with rising lake levels before declining to trace levels by ∼3000 cal yr BP. Increases in the abundance of non-arboreal pollen between ∼8500 and ∼4500 cal yr BP at the more eastern lakes suggest relatively delayed and truncated PFE influence, before the reestablishment of primarily boreal taxa by ∼4500 cal yr BP, coincident with diatom-inferred increases in lake levels. This study shows that the PFE moved both farther east and north than previously determined, but generally agrees with established patterns in vegetation from other studied regions along the PFE. [ABSTRACT FROM AUTHOR]

Abstract: Paleolimnological techniques are important for determining background ecological conditions and ecosystem responses to stressors when long-term data sets are absent. Research at the Dorset Environmental Sciences Centre (Ontario, Canada) [...]

Abstract: Diatom-based paleolimnological techniques were used to reconstruct lake acidification trends in 51 Lowalkalinity Nova Scotia lakes that spanned gradients of dissolved organic carbon (DOC) concentrations and sulphate deposition. Pre-industrial, [...]

Abstract: New Brunswick lakes are subjected to multiple environmental stressors, such as atmospheric acid deposition and climate change. In the absence of long-term environmental data, the impacts of these stressors [...]