We wish to thank the many partners and supporters of the NSERC LakePulse Network, as well as the Natural Sciences and Engineering Research Council (NSERC, Canada) for funding the project and BEB in the form of a Discovery Grant. IGE also acknowledges support from the Canada Research Chair program. We thank the Group for Interuniversity Research in Limnology (Groupe de recherche interuniversitaire) and their funders, the Fonds de recherche -nature et technologie (FRQNT, Québec) and the Faculty of Science at the University of Québec at Montréal for PhD stipend and scholarship support to CP. We thank the field teams who put in a great effort to sample the lakes, and landowners, including several First Nations, who welcomed our sampling.We would like to thank BSA environmental services for the zooplankton identification.Thanks to all the students, post-doctoral fellows and research professionals who contributed to the project; particularly Katherine Velghe, Marie-Pierre Varin, Maxime Fradette and Jelena Juric for their significant contributions to data generation and analyses, field coordination and database management. Finally, we thank Yannick Huot for directing the LakePulse project. BIOSKETCH: CINDY PAQUETTE is a PhD student part of the NSERC LakePulse network undertaking her studies in the Department of Biology at UQAM, co-supervised by I.G.-E. (McGill University) and B.E.B. TITLE: Zooplankton biogeography across temperate to subarctic regions: taxonomic and functional perspectives RUNNING TITLE: Canadian zooplankton biogeography ABSTRACT Aim: We examined variation in crustacean zooplankton taxonomic and functional composition and diversity across Canadian lakes. In addition to α-diversity patterns, we also explore mechanisms behind β-diversity spatial variation, using taxonomic and functional metrics. Location: Canada.

Aim: While it is now well accepted that human activities are having pronounced effects on natural ecosystems, regional variation in the rate and magnitude of various human impacts is unclear. Moreover, the effects of land use change on natural aquatic communities have only relatively recently begun to be explored. Our goal was to understand how and where assemblages of a central food web component of freshwater lakes have changed over the course of industrialization in relation to land use.Location: Canada.

Canada is home to more lakes than any other nation, but there is a fragmented and limited understanding of the ecological status of these water bodies. Zooplankton are excellent bioindicators of lake health, given their central food web position. To date, many studies have investigated the effect of individual stressors on zooplankton communities, mediated through changes in water quality (e.g., macronutrients, temperature, or chemicals). Increasingly, stressors act simultaneously in lakes, often over extended periods of time. As part of the NSERC Canadian Lake Pulse Network project, pelagic zooplankton were sampled in 624 lakes across Canada, spanning six continental drainage basins. We evaluated the effect of 40+ environmental variables on zooplankton diversity and community composition, considering both taxonomic and functional approaches. We also tested specific hypotheses on the relationships between zooplankton communities and environmental conditions, including eutrophication, calcium, chloride, and fish predation. We found that lake morphometry variables were among the most important predictors of zooplankton diversity, while water quality metrics were more critical in explaining variation in community composition. Our results also reveal significant heterogeneity across Canada, with contrasting effects of environmental drivers among continental watersheds, highlighting that response models cannot be assumed to apply universally.

No abstract

Studies examining the consequences of increased partial pressure of carbon dioxide (pCO2) in freshwater ecosystems associated with climate change have focused on direct effects for phytoplankton, showing increases in primary productivity, biomass or altered composition. However, in lakes, phytoplankton dynamics are also regulated by zooplankton predation and thermal stratification which can lead to a concentration of phytoplankton biomass in a deep chlorophyll maximum (DCM) layer, making the response to CO2 increase important to understand here. Mesocosm experiments were conducted in a meso‐oligotrophic north temperate lake with a strong summer phytoplankton DCM, to estimate the independent and interaction effects of zooplankton grazing and elevated pCO2 on water column phytoplankton communities and on DCM characteristics. Interaction of CO2 effects with zooplankton grazing occurred for three of four phytoplankton spectral groups, influencing water column phytoplankton biomass. Zooplankton selective grazing appeared as important as CO2 concentration in controlling phytoplankton population and biomass. Unexpectedly, CO2 had an overall negative effect on phytoplankton total biomass despite positive productivity responses. Elevated CO2 led to more peaked (stronger vertical gradient) mid‐water column chlorophyll distribution, but to smaller DCM peaks overall. Zooplankton had unexpected effects, inducing clustering of more edible phytoplankton and greater temporal variation in the DCM. Our experiment points to interactions in the microbial food web and stoichiometric considerations with nutrient addition that should be explored further in future work with realistic lake food webs to better understand these complex responses to CO2.

The alteration of environmental conditions has two major outcomes on the demographics of living organisms: population decline of the common species and extinction of the rarest ones. Halting the decline of abundant species as well as the erosion of biodiversity require solutions that may be mismatched, despite being rooted in similar causes. In this study, we demonstrate how rank abundance distribution (RAD) models are mathematical representations of a dominance-diversity dilemma. Across 4,375 animal communities from a range of taxonomic groups, we found that a reversed RAD model correctly predicts species richness, based solely on the relative dominance of the most abundant species in a community and the total number of individuals. Overall, predictions from this RAD model explained 69% of the variance in species richness, compared to 20% explained by simply regressing species richness on the relative dominance of the most abundant species. Using the reversed RAD model, we illustrate how species richness is co-limited by the total abundance of a community and the relative dominance of the most common species. Our results highlight an intrinsic trade-off between species richness and dominance that is present in the structure of RAD models and real-world animal community data. This dominance-diversity dilemma suggests that withdrawing individuals from abundant populations might contribute to the conservation of species richness. However, we posit that the positive effect of harvesting on biodiversity is often offset by exploitation practices with negative collateral consequences, such as habitat destruction or species bycatches.

Covering 55% of Canada’s total surface area and stretching from coast to coast to coast, the Canadian boreal zone is crucial to the nation’s economic and ecological integrity. Although often viewed as relatively underdeveloped, it is vulnerable to numerous stressors such as mining, forestry, and anthropogenic climate change. Natural archives preserved in lake sediments can provide key insights by quantifying pre-disturbance conditions (pre-1850 CE) and the nature, magnitude, direction, and speed of environmental change induced by anthropogenic stressors over the past ~150 years. Here, we paired a review of paleolimnological literature of the Canadian boreal zone with analyses of published sediment core data to highlight the effects of climate change, catchment disturbances, and atmospheric deposition on boreal lakes. Specifically, we conducted quantitative syntheses of two lake health indicators: elemental lead (Pb) and chlorophyll <i>a</i>. Segmented regressions and Mann-Kendall trend analysis revealed a generally increasing trend in elemental Pb across the boreal zone until ~1970 CE, followed by a generally decreasing trend to the present. Snapshot comparisons of sedimentary chlorophyll <i>a</i> from recent and pre-industrial sediments (i.e., top-bottom sediment core design) revealed that a majority of sites have increased over time, suggesting a general enhancement in lake primary production across the boreal zone. Collectively, this body of work demonstrates that long-term sediment records offer a critical perspective on ecosystem change not accessible through routine monitoring programs. We advocate using modern datasets in tandem with paleolimnology to establish baseline conditions, measure ecosystem changes, and set meaningful management targets.

No abstract