Dorset Environmental Science Center

Dorset, Canada

Dorset Environmental Science Center

Dorset, Canada

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Palmer M.E.,York University | Palmer M.E.,Environment Canada | Yan N.D.,York University | Yan N.D.,Dorset Environmental Science Center | Somers K.M.,Dorset Environmental Science Center
Climatic Change | Year: 2014

Using a 25-year record of monitoring data, we show that recent climate change has affected the thermal properties and oxygen content of seven lakes in south-central Ontario, Canada, and five lakes in north-central Wisconsin, USA. Coherent patterns in autumnal lake warming were driven by increased autumn air temperature in both lake districts. Temperature increases were restricted to the epilimnion and metalimnion of the lakes, resulting in increased thermal stability of the water column. Mixing depths also decreased over the study period. Shallower mixing depths in the Ontario lakes were due to climate-driven increases in lake-water dissolved organic carbon concentrations. Collectively, changes in the thermal regime of the lakes suggest autumn mixing of the water column may be delayed. Metalimnetic oxygen also increased in the Wisconsin lakes, perhaps in response to increased algal production as lake thermal regimes changed. The response of individual lakes to climate change was modified by lake chemistry in the Ontario lake district and by lake chemistry and morphometry in the Wisconsin lake district. Our results demonstrate coherent lake response to climate change and highlight the importance of both regional and local factors in regulating individual lake response to global climate change. © 2014 Springer Science+Business Media Dordrecht.


Palmer M.E.,York University | Yan N.D.,York University | Yan N.D.,Dorset Environmental Science Center
Freshwater Biology | Year: 2013

Ecological integrity is increasingly threatened by multiple anthropogenic stressors, but the cumulative impact of stressors is poorly understood because they can interact in unexpected ways. Knowledge of these interactions and their associated impacts is needed to support the conservation of valued ecosystems. We used a large-scale, replicated field survey and multiple regression analysis to investigate the cumulative impacts of multiple physical, chemical and biological stressors on the crustacean zooplankton assemblages of 34 Canadian Shield lakes between 1980s and 2004-2005. Zooplankton total abundance, species richness, diversity and community structure, as well as the relative abundances of prominent taxonomic orders of zooplankton, changed at a regional scale. These changes occurred in response to changes in water quality and lake thermal regime, and invasion by an exotic predator. Interactions between stressors were common and represented an important determinant of zooplankton assemblage changes over time. We provide the first evidence that the individual and combined impacts of multiple stressors cause regional ecological change over decades. Our results demonstrate the prevalence of stressor interactions in natural environments and highlight the complexity of ecosystem responses to multiple stressors. Zooplankton changes recorded here may be widespread because climate change, acidification, development and the spread of invasive species are globally pervasive. These changes could have cascading impacts because zooplankton is an essential link in aquatic food webs. Our findings highlight the need to consider the interactive effect of stressors when assessing anthropogenic impacts and will inform management and conservation of ecosystems threatened by multiple stressors. © 2013 John Wiley & Sons Ltd.


Kim N.,York University | Yan N.D.,Dorset Environmental Science Center
Limnology and Oceanography: Methods | Year: 2010

The invasive spiny water flea's (Bythotrephes longimanus) current North American distribution encompasses the Laurentian Great Lakes as well as a number of inland lakes, particularly on the Canadian Shield. In the past, poor survival in the laboratory has precluded controlled long-term studies on Bythotrephes. Here we investigated field collection techniques and choices of culture media, temperature, and diet that led to the successful maintenance of Bythotrephes from birth to reproduction. Gravid parthenogenic females were collected from invaded lakes. Resulting offspring were reared in source lake water filtered through 20 or 80 μm, or a fully defined artificial culture medium, FLAMES. Individuals raised in FLAMES produced significantly larger broods than those in lake water, indicating that it is an appropriate culture medium. We next conducted a 96-h temperature bioassay on juvenile Bythotrephes. Survival was comparable at 16°C, 20°C, and 24°C but decreased after 48 h at 28°C, and most animals died after 24 h at 32°C. We also reared Bythotrephes at 16°C, 19°C, 22°C, and 25°C. Corresponding intrinsic rates of natural increase (r) for animals maintained to first brood release were 0.02, 0.05, 0.06, and 0.03 d-1, suggesting that Bythotrephes should be reared at ~22°C to benefit from maximum population increases. Feeding trials confirmed that young Bythotrephes prefer small, slow-moving prey. Finally, we devised a protocol for rearing Bythotrephes that yielded 100% survival to reproduction and r = 0.10 d-1 (for animals maintained to first brood release). Given these results, it is now possible to conduct long-term laboratory studies on this invader. © 2010, by the American Society of Limnology and Oceanography, Inc.


Yan N.D.,York University | Yan N.D.,Dorset Environmental Science Center | Leung B.,McGill University | Lewis M.A.,University of Alberta | Peacor S.D.,Michigan State University
Biological Invasions | Year: 2011

More than most sub-disciplines of ecology, the study of biological invasions is characterized by breadth rather than by depth. Studies of expanding ranges of invaders are common, as are post-invasion case studies, but we rarely have a deep understanding of the dynamics and regulators of the processes of invasion and resultant ecological transformations. This is unfortunate because such depth may well be needed to develop targeted, knowledge-based, management plans. In this collection we provide this needed depth of study of the key aspects of the invasion process for the spiny water flea, Bythotrephes longimanus. We do so by presenting the results of the work conducted by researchers in the Canadian Aquatic Invasive Species Network (CAISN), and several of their American and European collaborators over the past half decade. Given its rapid spread in the Great Lakes basin in North America, and the decreases in pelagic biodiversity that have ensued, the last decade has witnessed a surge of research on Bythotrephes. In this collection we learn much about mechanisms and dynamics of its spread, about the key role of humans in that spread, about the importance of Allee effects to establishment and persistence, about choices and parameterization of risk assessment models, about the value of comparing "effects" in native and invaded regions, about complex probable interactions of the invasion with impending changes in the climate, and about the regulators of the invader's abundance and impacts. There should be much of interest in the collection for aquatic ecologists and invading species biologists alike. © 2011 Springer Science+Business Media B.V.


Piscia R.,National Research Council Italy | Yan N.D.,York University | Yan N.D.,Dorset Environmental Science Center | Manca M.M.,National Research Council Italy
Journal of Limnology | Year: 2016

The goal of this study was to improve the understanding of the large-scale mechanisms underlying the recovery of the zooplankton of Lake Orta from historical contamination, following reduced input of ammonia and metals and the subsequent 1989/90 liming intervention. The industrial pollution had been severe and long-lasting (1929-1990). Zooplankton biodiversity has improved, but most of the new taxa appearing in our counts are rotifers, while many calanoids and the large cladoceran predators (Bythotrephes and Leptodora) that are common in the nearby Lake Maggiore, were still absent from Lake Orta 17 years after liming. To aid understanding of the large-scale mechanisms controlling changes in annual richness, we assessed the annual persistence (P) of Crustacea and Rotifera taxa as an estimator of whether propagules that survived introduction, as result of the natural recolonization process, also thrived. We found that the rate of introduction of zooplankton colonists and their persistence in the water column of Lake Orta changed from 1971 to 2007. New rotifer taxa appeared in the lake after the mid-1980s, when discharge of toxic substances decreased, but their annual persistence was low (P<0.5) until the turn of the century. The numerical values of rotifer and crustacean persistence in Lake Orta were unexpectedly high in 2001 and 2007 (0.55 and 0.72 for rotifers, 0.85 and 0.86 for crustacean, respectively), much higher than in limed lakes in Sudbury, Canada, and in adjacent Lake Maggiore. We hypothesize this could be related to the lack of Cladoceran predators and zooplanktivorous fish in the pelagic waters of Lake Orta. © 2016, Page Press Publications. All rights reserved.


Celis-Salgado M.P.,York University | Keller W.B.,Laurentian University | Yan N.D.,York University | Yan N.D.,Dorset Environmental Science Center
Journal of Limnology | Year: 2016

Smelting of sulphur-rich metallic ores in Sudbury, Ontario, Canada, has caused acidification and metal contamination of thousands of lakes in the region. Recent reductions in smelter emissions have resulted in much ecological recovery, but the recovery of Daphnia species has been poor. To determine if Cu and Ni toxicity could explain differences in daphniid recovery among lakes, we compared results of 14 d static with renewal bioassays in waters from Blue Chalk Lake, an uncontaminated reference lake 200 km from Sudbury, and from five Sudbury lakes ranging in distance from the smelters and varying in metal and cation concentrations. We spiked Blue Chalk Lake water with Cu and Ni to levels resembling those of the Sudbury lakes and also tested the lake waters for toxicity. Survival of Daphnia pulex, D. pulicaria and D. mendotae decreased monotonically with increasing metal concentrations in the spiked Blue Chalk Lake treatments, falling from 90% in the controls to 0% at the two highest Cu and Ni levels, reflecting levels of Middle and Hannah lakes. In contrast, survival in waters collected from the actual Sudbury lakes did not monotonically track their total metal concentrations. Rather, survival fell to 0% in Clearwater Lake water, a lake with intermediate metal contamination (8.9 and 79.9 µg L–1 of Cu and Ni, respectively) vs 70-100% in the other lakes. We performed an additional assay with Clearwater Lake waters increasing its Ca and Na concentrations, singly and in combination to levels that reflected the levels in Middle Lake. The survival of the four daphniid species increased from 0% up to 80-100% with added Ca and from 0% to 60-90% with added Na. Lipid-ovarian indices had a similar trend to survival for D. mendotae and D. pulicaria in Bioassay 1, varying with the cation concentrations in the lakes for the daphniids in Bioassay 2. The bioassays results imply that regional recovery patterns of daphniids in Sudbury lakes cannot be understood without as a minimum considering both metal and base cation concentration differences among lakes, and give an indication of differences among Daphnia species to cope with metal stress. © 2016, Page Press Publications. All rights reserved.


Weisz E.J.,York University | Yan N.D.,York University | Yan N.D.,Dorset Environmental Science Center
Biological Invasions | Year: 2010

The abundance of the native, pelagic macroinvertebrate predator, Leptodora kindtii, is negatively correlated with the abundance of a new invasive competitor, Bythotrephes longimanus, in a small number of Canadian Shield lakes. However, we do not yet know if Bythotrephes is replacing Leptodora on a regional scale. We determined the distribution of both species in 166 lakes in the District of Muskoka, south-central Ontario, Canada-the watershed with the longest history and largest prevalence of Bythotrephes invasions in North America. The frequency of occurrence of Leptodora was substantially reduced (twofold) in the presence of Bythotrephes. We argue that Bythotrephes is responsible for this dramatic reduction in the frequency of occurrence of Leptodora. Lakes in which both species co-occurred could not be distinguished from invaded lakes without Leptodora, suggesting a pattern of species replacement at a watershed level. We believe this is the first account of the widespread replacement of a native, pelagic macroinvertebrate predator by Bythotrephes in North America, and it does not bode well for Leptodora given the rapid, ongoing spread of Bythotrephes. © 2010 Springer Science+Business Media B.V.


Weisz E.J.,York University | Yan N.D.,York University | Yan N.D.,Dorset Environmental Science Center
Canadian Journal of Fisheries and Aquatic Sciences | Year: 2010

The Eurasian aquatic invader Bythotrephes longimanus has spread rapidly throughout the Great Lakes watershed, particularly in Ontario, Canada, since its introduction in 1982. To date, the documentation of its spread has been largely anecdotal, not the result of planned surveys, so the actual distribution of the invader and the determinants of its distribution in Ontario remain uncertain. We surveyed 193 lakes in south-central Ontario to determine the importance of lake size, lake location, hydrological connection, and various physical, chemical, and human activity parameters in predicting the spread of Bythotrephes within the 1600-lake Muskoka watershed, North America's most heavily invaded lake region. Invaded lakes were larger than uninvaded lakes and had less acidic, more nutrient-poor, clearer waters. Contingency analyses indicated that invaded lakes were more accessible to humans and had more heavily developed shorelines. Shoreline coverage by cottages was the strongest predictor of Bythotrephes presence when all physical, chemical, and human use variables were included in a logistic regression model. Our results support the growing consensus that humans are primarily responsible for the spread of Bythotrephes.


Preston N.D.,University of Wisconsin - Madison | Rusak J.A.,Dorset Environmental Science Center
Hydrobiologia | Year: 2010

G. Evelyn Hutchinson proposed that external control by climate limits the fundamental productivity and the possible diversity of ecological communities. These climatic drivers are currently changing as a result of human activity, which may herald a shift in the influence of climate on global ecosystems. Long-term records reveal a reduction in ice cover on northern lakes over the last several centuries. Hence, we explore whether inter-annual climatic variability, represented by ice cover, influences the productivity and diversity of zooplankton communities in long-term datasets for five lakes in Northern Wisconsin. We used a multilevel modeling approach to test three predictions: (1) density will increase, (2) diversity will increase, and (3) community composition will be altered. We found an inverse relationship between ice-off date and annual zooplankton density. Daphnia density, for example, was inversely related to ice-off date, with 10-fold variability across the gradient of ice-off dates in Northern Wisconsin. In contrast, we did not observe a consistent shift in diversity or community structure. Thus, from ice cover records of northern lakes we found support for Hutchinson's idea that external climatic forces may regulate aquatic productivity; however, the response was numeric and we did not find evidence that lakes moved closer to maximum diversity on an inter-annual scale. © 2010 Springer Science+Business Media B.V.


Gray D.K.,Queen's University | Arnott S.E.,Queen's University | Shead J.A.,Dorset Environmental Science Center | Derry A.M.,University of Quebec at Montréal
Freshwater Biology | Year: 2012

Acidification has damaged biota in thousands of lakes and streams throughout eastern North America. Fortunately, reduced emissions of sulphur dioxide and nitrogen oxides beginning in the 1960s have allowed pH levels in many affected systems to increase. Determining the extent of biological and pH recovery in these systems is necessary to assess the success of emissions reductions programmes. Although there have been promising signs of biological recovery in many systems, recovery has occurred more slowly than expected for some taxa. Past studies with crustacean zooplankton indicate that a mixture of local abiotic variables, biotic variables and dispersal processes may influence the structure of recovering communities. However, most studies have been unable to determine the relative importance of these three groups of variables. We assessed chemical and biological recovery of acid-damaged lakes in Killarney Park, Ontario. In addition, we assessed the relative importance of local abiotic variables, biotic variables and dispersal processes for structuring recovering communities. We collected zooplankton community data, abiotic and biotic data from 45 Killarney Park lakes. To assess the recovery of zooplankton communities, we compared zooplankton data collected in 2005 to a survey conducted for the same lakes in 1972-73 using several univariate measures of community structure, as well as multivariate methods based on relative species abundances. To determine the factors influencing the structure of recovering zooplankton communities, we used hierarchical partitioning for univariate measures and spatial modelling and variation partitioning techniques for multivariate analyses. Our survey revealed significant pH increases for the majority of sampled lakes but univariate measures of community structure, such as species richness and diversity, indicated that only minor changes have occurred in many acid-damaged lakes. Hierarchical partitioning identified several variables that may influence our univariate measures of recovery, including pH, dissolved organic carbon (DOC) levels, fish presence/absence, lake surface area and lake elevation. 5.Multivariate methods revealed a shift in communities through time towards a structure more typical of neutral lakes, providing some evidence for recovery. Variation partitioning suggested that the structure of recovering copepod communities was influenced most by dispersal processes and abiotic variables, while biotic (Chaoborus densities, fish presence/absence) and abiotic variables were more important for cladoceran zooplankton. 6.Our results indicate that the recovery of zooplankton communities in Killarney Park is not yet complete, despite decades of emission reductions. The importance of variables related to acidification, such as pH and DOC, indicates that further chemical recovery may be necessary. The differing importance of abiotic, biotic and dispersal processes for structuring copepod versus cladoceran zooplankton might indicate that different management approaches and expectations for recovery are needed for these groups. © 2012 Blackwell Publishing Ltd.

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