Chironomid assemblages from the uppermost sediments of 435 lakes spanning northern North America were compared to environmental parameters using direct gradient analysis. This large calibration set was merged from several previously developed regional datasets, and increases the number of modern analogues that are available for use for paleoenvironmental interpretations in this region. Air temperature explained the largest amount of variation in the chironomid assemblages with several other environmental factors accounting for statistical significant amounts of the remaining variance. A robust inference model for deriving past mean July air temperatures from subfossil chironomid assemblages was developed and applied to previously published paleoclimate reconstructions from the High-Arctic, Middle-Arctic, Boreal treeline, and Alpine regions of northern North America. The patterns of the temperature reconstructions from the combined dataset were generally similar to the original reconstructions, but with colder inferred temperatures reflecting the incorporation of a larger number of modern sites from colder climates in the combined dataset. This analysis demonstrated that the larger temperature gradient available in the new training set, when compared to the temperature gradients in the original training sets, provides a better estimation of chironomid-environment relationships. In particular, the optima and tolerances estimated using the larger, combined dataset should be more accurate, and therefore, improve midge-based paleoclimate reconstructions for northern North America. Despite the much larger spatial scale and greater associated environmental heterogeneity now incorporated in the combined dataset, this study suggests that in most cases the overarching constraint governing Electronic supplementary material The online version of this article (

Snowmelt is a crucial source of water for many shallow subarctic lakes, but climate models predict that snowfall will decrease in some regions, with profound ecological consequences. Here we use lake water isotope data across gradients of terrestrial vegetation cover (open tundra to closed forest) and topographic relief to identify lakes that are vulnerable to desiccation under conditions of low snowmelt runoff in two subarctic landscapes—Old Crow Flats, Yukon, and Hudson Bay Lowlands, Manitoba (Canada). Lakes located in low‐relief, open tundra catchments in both landscapes displayed a systematic, positive offset between directly measured lake water δ18O over multiple sampling campaigns and lake water δ18O inferred from cellulose in recently deposited surface sediments. We attribute this offset to a strong evaporative 18O‐enrichment response to lower‐than‐average snowmelt runoff in recent years. Notably, some lakes underwent near‐complete desiccation during midsummer 2010 following a winter of very low snowfall. Based on the paleolimnological record of one such lake, the extremely dry conditions in 2010 may be unprecedented in the past ~200 years. Findings fuel concerns that a decrease in snowmelt runoff will lead to widespread desiccation of shallow lakes in these landscapes.

An examination of the Chironomidae, the dominant aquatic invertebrate taxa found in Arctic lakes and ponds, was conducted to determine the environmental gradients that may limit their geographical distribution in the eastern Canadian Arctic. Subfossil chironomid head capsules, comprising 86 taxa, were sampled from surficial sediments of 63 lakes that spanned from tree line (northern Manitoba) across multiple regions within the eastern Canadian Arctic. Water chemistry and environmental data were then compared with chironomid assemblages using multivariate analysis. The distribution of chironomids was found to primarily follow a temperature gradient, but additional significant relationships were also found along a nutrient–productivity gradient. Several species of the Tribe Chironomini, which generally represent warm-water adapted taxa, were also found far beyond tree line in the southern Kivalliq region of Nunavut, indicating a more northerly range than previously known. While temperature and trophic status were found to strongly influence the distribution of some taxa, partially constrained gradient analysis indicates that specific chironomid taxa could be used to indicate a primary response to climate regardless of trophic status. This may allow for more holistic inferences of how aquatic communities may respond to climate change as the range of temperature dependant species expand into Arctic systems.

Widespread across northern permafrost landscapes, thermokarst ponds and lakes provide vital wildlife habitat and play a key role in biogeochemical processes. Stored in the sediments of these typically shallow and dynamic waterbodies are rich sources of paleoenvironmental information whose potential has not yet been fully exploited, likely because of concerns over stratigraphic preservation and challenges to develop reliable sediment core chronologies. Here, we present an overview of recently derived informative paleolimnological reconstructions based on multiparameter analysis of sediment archives from permafrost aquatic basins. We include examples from across the Canadian North, Alaska, and Siberia that illustrate their value for providing insights into temporal patterns of lake inception, catchment erosion, aquatic productivity, hydrological evolution, and landscape disturbances. Although not captured in our survey, emerging research directions focused on carbon accumulation, storage, and balance hold much promise for contributing to global climate change science.Key words: thermokarst lakes, permafrost, paleolimnology, lake sediments.Résumé : Répandus d'un paysage de pergélisol septentrional à l'autre, les étangs et les lacs thermokarstiques fournissent un habitat essentiel à la faune et jouent un rôle clé dans les processus biogéochimiques. Accumulées dans les sédiments de ces plans d'eau typiquement peu profonds et dynamiques se trouvent des sources riches en informations paléoenvironne-mentales dont le potentiel n'a pas encore été entièrement exploité, probablement à cause des préoccupations concernant la conservation stratigraphique et les défis de développer des chronologies fiables à partir des carottes sédimentaires. Ici, nous présentons une vue d'ensemble des reconstitutions paléolimnologiques informatives récemment dérivées d'après l'analyse multi paramétrée d'archives de sédiments des bassins aquatiques du pergé-lisol. Nous incluons des exemples provenant du Nord canadien, de l'Alaska et de la Sibérie qui For personal use only.illustrent que ceux-ci peuvent offrir des perspectives sur les tendances temporelles de création de lacs, de l'érosion de bassins versants, de la productivité aquatique, de l'évolution hydrologique et des perturbations du paysage. Bien que non mises en lumière dans notre enquête, les directions de recherche émergentes centrées sur l'accumulation, le stockage et le bilan carbone s'annoncent bien quant à leur contribution à la science du changement climatique mondial.

Anthropogenic activities have led to a global decline in biodiversity, and monitoring studies indicate that both insect communities and wetland ecosystems are particularly affected. However, there is a need for long‐term data (over centennial or millennial timescales) to better understand natural community dynamics and the processes that govern the observed trends. Chironomids (Insecta: Diptera: Chironomidae) are often the most abundant insects in lake ecosystems, sensitive to environmental change, and, because their larval exoskeleton head capsules preserve well in lake sediments, they provide a unique record of insect community dynamics through time. Here, we provide the results of a metadata analysis of chironomid diversity across a range of spatial and temporal scales. First, we analyse spatial trends in chironomid diversity using Northern Hemispheric data sets overall consisting of 837 lakes. Our results indicate that in most of our data sets, summer temperature (Tjul) is strongly associated with spatial trends in modern‐day chironomid diversity. We observe a strong increase in chironomid alpha diversity with increasing Tjul in regions with present‐day Tjul between 2.5 and 14°C. In some areas with Tjul > 14°C, chironomid diversity stabilizes or declines. Second, we demonstrate that the direction and amplitude of change in alpha diversity in a compilation of subfossil chironomid records spanning the last glacial–interglacial transition (~15,000–11,000 years ago) are similar to those observed in our modern data. A compilation of Holocene records shows that during phases when the amplitude of temperature change was small, site‐specific factors had a greater influence on the chironomid fauna obscuring the chironomid diversity–temperature relationship. Our results imply expected overall chironomid diversity increases in colder regions such as the Arctic under sustained global warming, but with complex and not necessarily predictable responses for individual sites.

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Shallow lakes are dominant features in subarctic and Arctic landscapes and are responsive to multiple stressors, which can lead to rapid changes in limnological regimes with consequences for aquatic resources. We address this theme in the coastal tundra region of Wapusk National Park, western Hudson Bay Lowlands (Canada), where climate has warmed during the past century and the Lesser Snow Goose (LSG; Chen caerulescens caerulescens) population has grown rapidly during the past ∽40 years. Integration of limnological and paleolimnological analyses documents profound responses of productivity, nutrient cycling, and aquatic habitat to warming at three ponds (“WAP 12”, “WAP 20”, and “WAP 21″), and to LSG disturbance at the two ponds located in an active nesting area (WAP 20, WAP 21). Based on multiparameter analysis of 210Pb-dated sediment records from all three ponds, a regime shift occurred between 1875 and 1900 CE marked by a transition from low productivity, turbid, and nutrient-poor conditions of the Little Ice Age to conditions of higher productivity, lower nitrogen availability, and the development of benthic biofilm habitat as a result of climate warming. Beginning in the mid-1970s, sediment records from WAP 20 and WAP 21 reveal a second regime shift characterized by accelerated productivity and increased nitrogen availability. Coupled with 3 years of limnological data, results suggest that increased productivity at WAP 20 and WAP 21 led to atmospheric CO2 invasion to meet algal photosynthetic demand. This limnological regime shift is attributed to an increase in the supply of catchment-derived nutrients from the arrival of LSG and their subsequent disturbance to the landscape. Collectively, findings discriminate the consequences of warming and LSG disturbance on tundra ponds from which we identify a suite of sensitive limnological and paleolimnological measures that can be utilized to inform aquatic ecosystem monitoring.