The jellification of north temperate lakes.

Calcium (Ca) concentrations are decreasing in softwater lakes across eastern North America and western Europe. Using long-term contemporary and palaeo-environmental field data, we show that this is precipitating a dramatic change in Canadian lakes: the replacement of previously dominant pelagic herbivores (Ca-rich Daphnia species) by Holopedium glacialis, a jelly-clad, Ca-poor competitor. In some lakes, this transformation is being facilitated by increases in macro-invertebrate predation, both from native (Chaoborus spp.) and introduced (Bythotrephes longimanus) zooplanktivores, to which Holopedium, with its jelly coat, is relatively invulnerable. Greater representation by Holopedium within cladoceran zooplankton communities will reduce nutrient transfer through food webs, given their lower phosphorus content relative to daphniids, and greater absolute abundances may pose long-term problems to water users. The dominance of jelly-clad zooplankton will likely persist while lakewater Ca levels remain low.This work was primarily supported by grants from the Natural Sciences and Engineering Research Council of Canada and funding from the Ontario Ministry of the Environment.This is the accepted manuscript. The final version is available at http://rspb.royalsocietypublishing.org/content/282/1798/20142449

Broad-scale lake expansion and flooding inundates essential wood bison habitat

Understanding the interaction between the response of a complex ecosystem to climate change and the protection of vulnerable wildlife species is essential for conservation efforts. In the Northwest Territories (Canada), the recent movement of the Mackenzie wood bison herd (Bison bison athabascae) out of their designated territory has been postulated as a response to the loss of essential habitat following regional lake expansion. We show that the proportion of this landscape occupied by water doubled since 1986 and the timing of lake expansion corresponds to bison movements out of the Mackenzie Bison Sanctuary. Historical reconstructions using proxy data in dated sediment cores show that the scale of recent lake expansion is unmatched over at least the last several hundred years. We conclude that recent lake expansion represents a fundamental alteration of the structure and function of this ecosystem and its use by Mackenzie wood bison, in response to climate change

Linking mean body size of pelagic Cladocera to environmental variables in Precambrian Shield lakes: A paleolimnological approach

Daphnia and Bosmina fragments were identified and measured in the surface sediments of 42 lakes in the Muskoka-Haliburton region of Ontario, Canada, in an attempt to identify environmental factors that may influence cladoceran body size. Specifically, pecten length on Daphnia post-abdominal claws, antennule length on Bosmina headshields, and carapace and mucro lengths of Bosmina carapaces were measured. These measurements were then compared to limnological variables previously identified as possibly influencing cladoceran size, including dissolved organic carbon (DOC), total phosphorus (TP), pH, calcium (Ca), Chaoborus density, and fish presence/absence. Cladoceran size displayed a linear relationship to TP, with larger Bosmina and Daphnia present in lakes with lower nutrient levels. We suspect that, as larger individuals are more efficient grazers, they may competitively exclude smaller individuals when nutrients are limiting in these lakes. Bosmina mucro length and cladoceran community size structure displayed a step response to DOC, with mean size significantly smaller when DOC concentrations were higher than 5.89 mg L-1. Daphnia pecten length displayed a negative linear relationship to DOC above a concentration of 4.90 mg l-1. Reduced predation pressure from gape-limited macroinvertebrate predators, such as Chaoborus, may have influenced these relationships. DOC was also highly correlated to TP in these lakes, and size trends might be responding to the TP gradient rather than the DOC gradient. Mean cladoceran body size in acidic lakes (pH < 6.0) was significantly smaller than mean body size in circumneutral lakes (pH > 6.0). There was no relationship between size structure and Ca concentrations, attributed to a narrow Ca gradient in these lakes. Predation effects were examined using limited Chaoborus density and fish presence/absence data. Although there were no significant relationships between cladoceran size and Chaoborus density, some significant relationships between size variables and fish predation were identified. The sensitivity of size variables to certain environmental gradients suggests that size structure has the potential to be an effective paleolimnological tool

Limnology and diatom ecology of shallow lakes in a rapidly thawing discontinuous permafrost peatland

Lakes in discontinuous permafrost peatlands are on the front lines of climate change, sensitive to even modest increases in air temperature. The aim of this study was to provide the first limnological characterization of shallow (∼1-2 m depth) lakes in the Scotty Creek basin (Northwest Territories, Canada), a field site of circumpolar significance due to the existence of long-term ecohydrological monitoring going back decades. We use this as a foundation from which to advance our process-based understanding of the potential drivers of lake ecosystem change. Our results showed that dissolved organic carbon (DOC) and lake color were not correlated, a pattern that appears to be an important driver of diatom (siliceous single-celled algae) assemblages in these lakes. Diatoms in the study lakes tended to fall into one of two assemblage clusters. One cluster, comprised of small benthic Fragilariaceae and small Navicula species (sensu lato), was found associated with higher lake color. The second cluster, comprised of Encyonopsis and large Navicula species, was found associated with high DOC, lower color, and the presence of a benthic moss mat. From this, we suggest that DOC quality is a primary control on lake ecology in this region for its role in controlling light penetration to the lake bottom. We hypothesized that the prevalence of nearshore fens and collapse scar wetlands would be important drivers of DOC, but this was not supported in the 9 study lakes for which we had available data to map shoreline features.</p

Multi-trophic level response to extreme metal contamination from gold mining in a subarctic lake

112 hlm.; ilus.; 21 c

Paleolimnology of thermokarst lakes: a window into permafrost landscape evolution

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 multi-parameter 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.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Longitudinal data from 8 Ontario lakes

We tested the mechanisms underlying increases in the relative and absolute abundance of Holopedium glacialis in the planktonic cladoceran assemblage of 8 central-Ontario, Canada lakes that were sampled monthly for 30 years. Zooplankton were sampled during the ice-free season near the point of maximum depth by using a metered, 76 μm mesh, tow net. The net was deployed in 4 to 7 vertical hauls and its contents were combined to produce a composite that corrected for the diminution of lake stratum volume with depth. A minimum of 250 crustacean zooplankton were enumerated in each composite, subsampling to ensure that no taxon comprised more than 10% of the total count. Phytoplankton were sampled through the euphotic zone, and water chemistry samples were volume-weighted composites of all depths during isothermal periods, and of the mixed layers during periods of vernal and autumnal stratification. Dissolved oxygen profiles were generated at 1-2 m intervals from all depths. Finally, abundances of the zooplanktivore, Chaoborus spp. were quantified in samples from night-time vertical hauls at 10 stations visited during the autumn in all lakes in 1986 and in one lake from 1987-1994. In the laboratory, a minimum of 300 cells, colonies, or filaments of phytoplankton were counted within the Bacillariophyceae, Chlorophyceae, Cryptophyceae, Dinophyceae, and Euglenophyceae. Dimensions of all counted algae were measured, and summed to express values as an "edible" phytoplankton biovolume