Neal Michelutti - Academia.edu (original) (raw)

Papers by Neal Michelutti

Air temperatures in the tropical Andes have risen at an accelerated rate relative to the global a... more Air temperatures in the tropical Andes have risen at an accelerated rate relative to the global average over recent decades. However, the effects of climate change on Andean lakes, which are vital to sustaining regional biodiversity and serve as an important water resource to local populations, remain largely unknown. Here, we show that recent climate changes have forced alpine lakes of the equatorial Andes towards new ecological and physical states, in close synchrony to the rapid shrinkage of glaciers regionally. Using dated sedi-ment cores from three lakes in the southern Sierra of Ecuador, we record abrupt increases in the planktonic thalassiosiroid diatom Discostella stelligera from trace abundances to dom-inance within the phytoplankton. This unprecedented shift occurs against the backdrop of rising temperatures, changing atmospheric pressure fields, and declining wind speeds. Ecological restructuring in these lakes is linked to warming and/or enhanced water column stratificat...

Proceedings of the National Academy of Sciences, 2020

Significance Globally, seabird populations are in decline. Without long-term monitoring, realisti... more Significance Globally, seabird populations are in decline. Without long-term monitoring, realistic conservation goals are difficult to establish. Here, we use lake sediment records to reconstruct the long-term dynamics of an important colony of Leach’s Storm-petrels. We show that this seabird population underwent moderate natural population fluctuations until Europeans settled near the colony, after which seabird numbers were dramatically reduced. Our approach provides data concerning shifting baselines in conservation by demonstrating that the colony is only ∼16% of the potential carrying capacity, and thus, reasonable conservation goals should be based on preindustrialization population sizes. Likely, numerous other seabirds are also unknowingly in decline, highlighting the need for longer-term data and the immediate need to protect and rehabilitate the critical habitat.

Scientific Reports, 2019

Dissolved organic carbon (DOC) concentrations and water colour are increasing in many inland wate... more Dissolved organic carbon (DOC) concentrations and water colour are increasing in many inland waters across northern Europe and northeastern North America. This inland-water “browning” has profound physical, chemical and biological repercussions for aquatic ecosystems affecting water quality, biological community structures and aquatic productivity. Potential drivers of this “browning” trend are complex and include reductions in atmospheric acid deposition, changes in land use/cover, increased nitrogen deposition and climate change. However, because of the overlapping impacts of these stressors, their relative contributions to DOC dynamics remain unclear, and without appropriate long-term monitoring data, it has not been possible to determine whether the ongoing “browning” is unprecedented or simply a “re-browning” to pre-industrial DOC levels. Here, we demonstrate the long-term impacts of acid deposition and climate change on lake-water DOC concentrations in low and high acid-deposi...

Aquatic Sciences, 2018

Arctic freshwater ponds are typically pristine and oligotrophic, however, seabird biovectors can ... more Arctic freshwater ponds are typically pristine and oligotrophic, however, seabird biovectors can markedly alter water quality via enrichment with marine-derived nutrients and bioaccumulated metals. These ornithogenic inputs can be the dominant factor structuring aquatic biota and the surrounding island flora. Here, we measured a suite of limnological water chemistry variables and sediment geochemistry from 21 freshwater ponds influenced by Common Eiders (Somateria mollissima) in Hudson Strait, near the northern communities of Cape Dorset (Nunavut) and Ivujivik (Quebec). Nest counts and sedimentary δ 15 N values were used as proxies of bird abundance. Nutrientrich guano from the nesting eiders visibly promoted the growth of catchment vegetation. Elevated metal (Al, Cd, Zn), metalloid (Se), and nutrient concentrations (N, P) in the water of eider-affected sites were recorded (Sign test; p = 0.004), but the proximity of many sites to the coast meant that variables related to ocean spray (conductivity, Na + , Mg 2+ , Cl-, Sr) confounded the effects of birds on pond water chemistry. In contrast, sediment geochemistry appeared to more clearly characterize sites according to the level of eider activity in their catchments by tracking Pb, Cd, N, and P sedimentary concentrations (Sign test; p = 0.02). These results have direct implications for reconstructing historical eider population trends using sediment archives, which is necessary to inform effective conservation management strategies.

Proceedings. Biological sciences, Jan 25, 2018

With the expansion of urban centres in the mid-twentieth century and the post-1970 decrease in pe... more With the expansion of urban centres in the mid-twentieth century and the post-1970 decrease in pesticides, populations of double-crested cormorants () and ring-billed gulls () around Lake Ontario (Canada and USA) have rapidly rebounded, possibly to unprecedented numbers. Along with the use of traditional palaeolimnological methods (e.g. stable isotopes, biological proxies), we now have the capacity to develop specific markers for directly tracking the presence of waterbirds on nesting islands. Here, we apply the use of lipophilic sterols and stanols from both plant and animal-faecal origins as a reliable technique, independent of traditional isotopic methods, for pinpointing waterbird arrival and population growth over decadal timescales. Sterol and stanol concentrations measured in the guano samples of waterbird species were highly variable within a species and between the three species of waterbirds examined. However, cholesterol was the dominant sterol in guano, and phytosterols ...

Environmental science & technology, Jan 3, 2017

Changing lake water total organic carbon (TOC) concentrations are of concern for lake management ... more Changing lake water total organic carbon (TOC) concentrations are of concern for lake management because of corresponding effects on aquatic ecosystem functioning, drinking water resources and carbon cycling between land and sea. Understanding the importance of human activities on TOC changes requires knowledge of past concentrations; however, water-monitoring data are typically only available for the past few decades, if at all. Here, we present a universal model to infer past lake water TOC concentrations in northern lakes across Europe and North America that uses visible-near-infrared (VNIR) spectroscopy on lake sediments. In the orthogonal partial least-squares model, VNIR spectra of surface-sediment samples are calibrated against corresponding surface water TOC concentrations (0.5-41 mg L(-1)) from 345 Arctic to northern temperate lakes in Canada, Greenland, Sweden and Finland. Internal model-cross-validation resulted in a R(2) of 0.57 and a prediction error of 4.4 mg TOC L(-1)...

PloS one, 2017

Recent climate change has been especially pronounced in the High Arctic, however, the responses o... more Recent climate change has been especially pronounced in the High Arctic, however, the responses of aquatic biota, such as diatoms, can be modified by site-specific environmental characteristics. To assess if climate-mediated ice cover changes affect the diatom response to climate, we used paleolimnological techniques to examine shifts in diatom assemblages from ten High Arctic lakes and ponds from Ellesmere Island and nearby Pim Island (Nunavut, Canada). The sites were divided a priori into four groups ("warm", "cool", "cold", and "oasis") based on local elevation and microclimatic differences that result in differing lengths of the ice-free season, as well as about three decades of personal observations. We characterized the species changes as a shift from Condition 1 (i.e. a generally low diversity, predominantly epipelic and epilithic diatom assemblage) to Condition 2 (i.e. a typically more diverse and ecologically complex assemblage with a...

Journal of Limnology, 2015

The tropical Andes are undergoing climate changes that rival those occurring anywhere else on the... more The tropical Andes are undergoing climate changes that rival those occurring anywhere else on the planet, and are likely to have profound consequences for ecosystems. Paleolimnological investigations of remote mountain lakes can provide details of past environmental change, especially where monitoring data are absent. Here, we reconstruct fossil diatom and chironomid communities spanning the last several hundred years from an Andean lake located in an ecological reserve near Quito, Ecuador. Both diatoms and chironomids recorded assemblage shifts reflective of changing climate conditions. The diatoms are likely responding primarily to temperature-related limnological changes, recording an increase in the number of planktonic taxa in the most recent sediments. This change is consistent with warmer conditions that result in enhanced periods of thermal stratification, allowing planktonic species to proliferate. The chironomids appear to respond mainly to a change in precipitation regime...

PLOS ONE, 2015

In the Laurentian Great Lakes region, the double-crested cormorant (Phalacrocorax auritus) has se... more In the Laurentian Great Lakes region, the double-crested cormorant (Phalacrocorax auritus) has seen a thousand-fold population increase in recent decades. These large colonies of birds now often conflict with socioeconomic interests, particularly due to perceived competition with fisheries and the destruction of terrestrial vegetation in nesting habitats. Here we use dated sediment cores from ponds on islands in eastern Lake Ontario that receive waste inputs from dense colonies of cormorants and ring-billed gulls (Larus delawarensis) to chronicle the population rise of these species and assess their long-term ecological impacts. Modern water chemistry sampling from these sites reveals drastically elevated nutrient and major ion concentrations compared to reference ponds not influenced by waterbirds. Geochemical tracers in dated sediment cores, particularly δ 15 N and chlorophyll-a concentrations, track waterbird influences over time. Fossil diatom assemblages were dominated by species tolerant of hyper-eutrophic and polluted systems, which is in marked contrast to assemblages in reference sites. In addition to establishing long-term ecological impacts, this multi-proxy paleoecological approach can be used to determine whether islands of concern have been long-term nesting sites or were only recently colonized by cormorant or ring-billed gull populations across the Great Lakes, facilitating informed management decisions about controversial culling programs.

Science of The Total Environment, 2009

Concentrations and stable isotope ratios of lead (Pb) from lake sediments were used to quantify t... more Concentrations and stable isotope ratios of lead (Pb) from lake sediments were used to quantify temporal patterns of anthropogenic Pb pollution in the Clyde River region of Baffin Island, Arctic Canada. Surface sediments from eight lakes on eastern Baffin Island and one from northern-most Greenland, spanning a gradient of 20°latitude, showed great variability with respect to Pb concentration and stable isotopic Pb ratios, with little apparent latitudinal trend. To constrain the temporal evolution of regional Pb pollution, a well-dated core from one of the sites, Lake CF8 on east-central Baffin Island, was analyzed geochemically at high stratigraphic resolution. A pronounced decrease in the 206 Pb/ 207 Pb ratio occurs in sediments deposited between 1923 and the mid-1970s, likely reflecting alkyl-Pb additives derived from the combustion of fossil fuels at a global scale. A two-component mixing model indicates that 17-26% of the Pb in the labile fraction of sediments deposited in Lake CF8 between 2001 and 2005 is from anthropogenic input. A Pb-Pb co-isotopic plot (206 Pb/ 207 Pb vs. 208 Pb/ 206 Pb ratios) of the Lake CF8 time series data indicates multiple possible sources of industrial Pb pollution. Despite widespread reductions in industrial Pb emissions since the 1970s, there is no evidence for attendant reductions of pollution Pb at Lake CF8. Enhanced scavenging from increased primary production as well as changing precipitation rates as climate warms may represent important factors that modulate Pb deposition to Lake CF8, and Arctic lakes elsewhere.

PLOS ONE, 2015

Air temperatures in the tropical Andes have risen at an accelerated rate relative to the global a... more Air temperatures in the tropical Andes have risen at an accelerated rate relative to the global average over recent decades. However, the effects of climate change on Andean lakes, which are vital to sustaining regional biodiversity and serve as an important water resource to local populations, remain largely unknown. Here, we show that recent climate changes have forced alpine lakes of the equatorial Andes towards new ecological and physical states, in close synchrony to the rapid shrinkage of glaciers regionally. Using dated sediment cores from three lakes in the southern Sierra of Ecuador, we record abrupt increases in the planktonic thalassiosiroid diatom Discostella stelligera from trace abundances to dominance within the phytoplankton. This unprecedented shift occurs against the backdrop of rising temperatures, changing atmospheric pressure fields, and declining wind speeds. Ecological restructuring in these lakes is linked to warming and/or enhanced water column stratification. In contrast to seasonally ice-covered Arctic and temperate alpine counterparts, aquatic production has not increased universally with warming, and has even declined in some lakes, possibly because enhanced thermal stability impedes the recirculation of hypolimnetic nutrients to surface waters. Our results demonstrate that these lakes have already passed important ecological thresholds, with potentially far-reaching consequences for Andean water resources.

Quaternary Science Reviews, 2012

Few lakes in the Arctic preserve sediments older than Holocene age because of pervasive glacial s... more Few lakes in the Arctic preserve sediments older than Holocene age because of pervasive glacial scour during the last ice age. Here we present sediment diatom and geochemical records from a lake on eastcentral Baffin Island (CF8, Nunavut, Canada) that captures three successive interglacial periods within the last 200,000 years: a portion of marine isotope stage (MIS) 7; the last interglacial (MIS 5e); and the Holocene (MIS 1). An additional unit of diatom-rich organic sediment occurs between the latter two intervals, and is ascribed to MIS 5a interstadial conditions. The Lake CF8 paleolimnological record reveals similar ontogenetic trends within each interglacial. Early postglacial environments in both the Holocene and MIS 5e were characterized by a dominance of colonial benthic fragilarioid diatoms that thrived in relatively alkaline waters. These species shifts do not coincide with major changes in base cation delivery to the sediments, suggesting that shifts in diatom assemblages are controlled mainly by climate-driven pH dynamics. Diatom assemblages then transitioned into dominance by tychoplanktonic Aulacoseira species, likely in response to climate-driven pH dynamics. The highest sustained abundances of Aulacoseira occur in sediments ascribed to MIS 5e, and this is the only interval in which thalassiosiroid centric taxa also occur (e.g. Discostella and Puncticulata spp.). Given that these planktonic taxa typically reach high abundances during extended periods of open-water conditions, we surmise that MIS 5e was the warmest interval recorded. The overall similarity of lake ontogenetic trajectories recorded within each interglacial period suggests that climatic and edaphic factors drive a complex succession of environmental changes through indirect effects on lake ice cover, habitat availability, and lake-water pH. In recent decades (past w50 yrs), an unprecedented increase in periphytic Eunotia taxa is evident; these diatoms were only present intermittently during previous glacialeinterglacial cycles. The expansion of Eunotia is attributed to increased habitat availability associated with declining ice cover during recent 20 th century warming. By integrating data from several distinct interglacials, the CF8 diatom record considerably extends our understanding of Arctic lake ontogeny, and provides an unparalleled natural archive with which to compare recent changes associated with anthropogenic climate warming.

Quaternary Research, 2006

A diatom-based paleolimnological investigation was conducted on late Holocene sediments from a po... more A diatom-based paleolimnological investigation was conducted on late Holocene sediments from a poorly buffered lake, informally named “Rock Basin Lake”, on Ellesmere Island, Arctic Canada. The fossil diatom record is unlike any other obtained thus far from high arctic regions, exhibiting dynamic assemblage shifts over the entire ∼3300 yr sedimentary record. Multiple proxies (i.e., diatoms, pH reconstructions, biogenic silica, C/N ratios, total organic carbon) appear to sensitively track rapid limnological changes, which are associated with distinct climate intervals as inferred from other regional proxy records. The highly responsive nature of the diatom assemblages in Rock Basin Lake, relative to those recorded from nearby alkaline sites, appears to be related to this lake's limited ability to buffer changes in pH. The dynamic species responses suggest that the diatoms in Rock Basin Lake are faithfully tracking climatic changes, and that low-alkalinity lakes may provide the mos...

Quaternary Research, 2006

Reconstructions of past environmental changes are critical for understanding the natural variabil... more Reconstructions of past environmental changes are critical for understanding the natural variability of Earth's climate system and for providing a context for present and future global change. Radiocarbon-dated lake sediments from Lake CF3, northeastern Baffin Island, Arctic Canada, are used to reconstruct past environmental conditions over the last 11,200 years. Numerous proxies, including chironomid-inferred July air temperatures, diatom-inferred lakewater pH, and sediment organic matter, reveal a pronounced Holocene thermal maximum as much as 5°C warmer than historic summer temperatures from ∼10,000 to 8500 cal yr B.P. Following rapid cooling ∼8500 cal yr B.P., Lake CF3 proxies indicate cooling through the late Holocene. At many sites in northeastern Canada, the Holocene thermal maximum occurred later than at Lake CF3; this late onset of Holocene warmth is generally attributed to the impacts of the decaying Laurentide Ice Sheet on early Holocene temperatures in northeastern C...

Proceedings of the Royal Society B: Biological Sciences, 2013

We document the rapid transformation of one of the Earth's last remaining Arctic refugia, a c... more We document the rapid transformation of one of the Earth's last remaining Arctic refugia, a change that is being driven by global warming. In stark contrast to the amplified warming observed throughout much of the Arctic, the Hudson Bay Lowlands (HBL) of subarctic Canada has maintained cool temperatures, largely due to the counteracting effects of persistent sea ice. However, since the mid-1990s, climate of the HBL has passed a tipping point, the pace and magnitude of which is exceptional even by Arctic standards, exceeding the range of regional long-term variability. Using high-resolution, palaeolimnological records of algal remains in dated lake sediment cores, we report that, within this short period of intense warming, striking biological changes have occurred in the region's freshwater ecosystems. The delayed and intense warming in this remote region provides a natural observatory for testing ecosystem resilience under a rapidly changing climate, in the absence of direc...

Proceedings of the Royal Society B: Biological Sciences, 2012

Numerous environmental pressures have precipitated long-term population reductions of many insect... more Numerous environmental pressures have precipitated long-term population reductions of many insect species. Population declines in aerially foraging insectivorous birds have also been detected, but the cause remains unknown partly because of a dearth of long-term monitoring data on avian diets. Chimney swifts ( Chaetura pelagica ) are a model aerial insectivore to fill such information gaps because their roosting behaviour makes them easy to sample in large numbers over long time periods. We report a 48-year-long (1944–1992) dietary record for the chimney swift, determined from a well-preserved deposit of guano and egested insect remains in Ontario (Canada). This unique archive of palaeo-environmental data reflecting past chimney swift diets revealed a steep rise in dichlorodiphenyltrichloroethane (DDT) and metabolites, which were correlated with a decrease in Coleoptera remains and an increase in Hemiptera remains, indicating a significant change in chimney swift prey. We argue that...

Proceedings of the Royal Society B: Biological Sciences, 2009

Migratory animals such as seabirds, salmon and whales can transport large quantities of nutrients... more Migratory animals such as seabirds, salmon and whales can transport large quantities of nutrients across ecosystem boundaries, greatly enriching recipient food webs. As many of these animals biomagnify contaminants, they can also focus pollutants at toxic levels. Seabirds arguably represent the most significant biovectors of nutrients and contaminants from the ocean to the land, given their sheer numbers and global distribution. However, long-term census data on seabirds are rare. Using palaeolimnological proxies, we show that a colony of Arctic seabirds has experienced climate-induced population increases in recent decades. We then document increasing concentrations of contaminants, including polychlorinated biphenyls and cadmium, in pond sediments that are linked to biotransport by seabirds. Our findings suggest that climate-related shifts in global seabird populations will have the unexpected consequence of restructuring coastal ecosystems.

Proceedings of the National Academy of Sciences, 2010

Seabirds represent a well documented biological transport pathway of nutrients from the ocean to ... more Seabirds represent a well documented biological transport pathway of nutrients from the ocean to the land by nesting in colonies and providing organic subsidies (feces, carcasses, dropped food) to these sites. We investigated whether seabirds that feed at different trophic levels vary in their potency as biovectors of metals, which can bioaccumulate through the marine foodweb. Our study site, located on a small island in Arctic Canada, contains the unique scenario of two nearby ponds, one of which receives inputs almost exclusively from upper trophic level piscivores (Arctic terns, Sterna paradisaea ) and the other mainly from lower trophic level molluscivores (common eiders, Somateria mollissima ). We used dated sediment cores to compare differences in diatoms, metal concentrations and also stable isotopes of nitrogen (δ 15 N), which reflect trophic position. We show that the seabirds carry species-specific mixtures of metals that are ultimately shunted to their nesting sites. For ...

Proceedings of the National Academy of Sciences, 2009

The Arctic is currently undergoing dramatic environmental transformations, but it remains largely... more The Arctic is currently undergoing dramatic environmental transformations, but it remains largely unknown how these changes compare with long-term natural variability. Here we present a lake sediment sequence from the Canadian Arctic that records warm periods of the past 200,000 years, including the 20th century. This record provides a perspective on recent changes in the Arctic and predates by approximately 80,000 years the oldest stratigraphically intact ice core recovered from the Greenland Ice Sheet. The early Holocene and the warmest part of the Last Interglacial (Marine Isotope Stage or MIS 5e) were the only periods of the past 200,000 years with summer temperatures comparable to or exceeding today's at this site. Paleoecological and geochemical data indicate that the past three interglacial periods were characterized by similar trajectories in temperature, lake biology, and lakewater pH, all of which tracked orbitally-driven solar insolation. In recent decades, however, t...

Limnology and Oceanography, 2011

We studied the effects of four decades of cultural eutrophication on Meretta Lake, in the Canadia... more We studied the effects of four decades of cultural eutrophication on Meretta Lake, in the Canadian High Arctic, through a multiproxy analysis of its sediments, including sedimentary pigments, metal concentrations, stable isotope ratios, chironomids, and diatoms. While Meretta Lake's biota clearly responded to nutrient inputs, the manner in which the changes differed from those expected in temperate lakes underlined the profound effects in Arctic lakes of extended ice and snow cover on light penetration, mixing, and interactions with the atmosphere. Hypolimnetic anoxia developed rapidly in Meretta Lake in response to sewage enrichment and was accompanied by the appearance of photosynthetic sulfur bacteria. Benthic communities responded rapidly to sewage inputs, but phytoplankton biomass did not increase until eutrophication was accompanied by climate warming, further reinforcing the importance of ice cover in controlling biotic processes in high Arctic lakes. With climate-mediated ice cover reductions in Meretta Lake, the response to eutrophication began to more closely resemble temperate processes. Recent trajectories indicate that slightly more than a decade after the cessation of sewage inputs, Meretta Lake is recovering toward pre-enrichment conditions.

Air temperatures in the tropical Andes have risen at an accelerated rate relative to the global a... more Air temperatures in the tropical Andes have risen at an accelerated rate relative to the global average over recent decades. However, the effects of climate change on Andean lakes, which are vital to sustaining regional biodiversity and serve as an important water resource to local populations, remain largely unknown. Here, we show that recent climate changes have forced alpine lakes of the equatorial Andes towards new ecological and physical states, in close synchrony to the rapid shrinkage of glaciers regionally. Using dated sedi-ment cores from three lakes in the southern Sierra of Ecuador, we record abrupt increases in the planktonic thalassiosiroid diatom Discostella stelligera from trace abundances to dom-inance within the phytoplankton. This unprecedented shift occurs against the backdrop of rising temperatures, changing atmospheric pressure fields, and declining wind speeds. Ecological restructuring in these lakes is linked to warming and/or enhanced water column stratificat...

Proceedings of the National Academy of Sciences, 2020

Significance Globally, seabird populations are in decline. Without long-term monitoring, realisti... more Significance Globally, seabird populations are in decline. Without long-term monitoring, realistic conservation goals are difficult to establish. Here, we use lake sediment records to reconstruct the long-term dynamics of an important colony of Leach’s Storm-petrels. We show that this seabird population underwent moderate natural population fluctuations until Europeans settled near the colony, after which seabird numbers were dramatically reduced. Our approach provides data concerning shifting baselines in conservation by demonstrating that the colony is only ∼16% of the potential carrying capacity, and thus, reasonable conservation goals should be based on preindustrialization population sizes. Likely, numerous other seabirds are also unknowingly in decline, highlighting the need for longer-term data and the immediate need to protect and rehabilitate the critical habitat.

Scientific Reports, 2019

Dissolved organic carbon (DOC) concentrations and water colour are increasing in many inland wate... more Dissolved organic carbon (DOC) concentrations and water colour are increasing in many inland waters across northern Europe and northeastern North America. This inland-water “browning” has profound physical, chemical and biological repercussions for aquatic ecosystems affecting water quality, biological community structures and aquatic productivity. Potential drivers of this “browning” trend are complex and include reductions in atmospheric acid deposition, changes in land use/cover, increased nitrogen deposition and climate change. However, because of the overlapping impacts of these stressors, their relative contributions to DOC dynamics remain unclear, and without appropriate long-term monitoring data, it has not been possible to determine whether the ongoing “browning” is unprecedented or simply a “re-browning” to pre-industrial DOC levels. Here, we demonstrate the long-term impacts of acid deposition and climate change on lake-water DOC concentrations in low and high acid-deposi...

Aquatic Sciences, 2018

Arctic freshwater ponds are typically pristine and oligotrophic, however, seabird biovectors can ... more Arctic freshwater ponds are typically pristine and oligotrophic, however, seabird biovectors can markedly alter water quality via enrichment with marine-derived nutrients and bioaccumulated metals. These ornithogenic inputs can be the dominant factor structuring aquatic biota and the surrounding island flora. Here, we measured a suite of limnological water chemistry variables and sediment geochemistry from 21 freshwater ponds influenced by Common Eiders (Somateria mollissima) in Hudson Strait, near the northern communities of Cape Dorset (Nunavut) and Ivujivik (Quebec). Nest counts and sedimentary δ 15 N values were used as proxies of bird abundance. Nutrientrich guano from the nesting eiders visibly promoted the growth of catchment vegetation. Elevated metal (Al, Cd, Zn), metalloid (Se), and nutrient concentrations (N, P) in the water of eider-affected sites were recorded (Sign test; p = 0.004), but the proximity of many sites to the coast meant that variables related to ocean spray (conductivity, Na + , Mg 2+ , Cl-, Sr) confounded the effects of birds on pond water chemistry. In contrast, sediment geochemistry appeared to more clearly characterize sites according to the level of eider activity in their catchments by tracking Pb, Cd, N, and P sedimentary concentrations (Sign test; p = 0.02). These results have direct implications for reconstructing historical eider population trends using sediment archives, which is necessary to inform effective conservation management strategies.

Proceedings. Biological sciences, Jan 25, 2018

With the expansion of urban centres in the mid-twentieth century and the post-1970 decrease in pe... more With the expansion of urban centres in the mid-twentieth century and the post-1970 decrease in pesticides, populations of double-crested cormorants () and ring-billed gulls () around Lake Ontario (Canada and USA) have rapidly rebounded, possibly to unprecedented numbers. Along with the use of traditional palaeolimnological methods (e.g. stable isotopes, biological proxies), we now have the capacity to develop specific markers for directly tracking the presence of waterbirds on nesting islands. Here, we apply the use of lipophilic sterols and stanols from both plant and animal-faecal origins as a reliable technique, independent of traditional isotopic methods, for pinpointing waterbird arrival and population growth over decadal timescales. Sterol and stanol concentrations measured in the guano samples of waterbird species were highly variable within a species and between the three species of waterbirds examined. However, cholesterol was the dominant sterol in guano, and phytosterols ...

Environmental science & technology, Jan 3, 2017

Changing lake water total organic carbon (TOC) concentrations are of concern for lake management ... more Changing lake water total organic carbon (TOC) concentrations are of concern for lake management because of corresponding effects on aquatic ecosystem functioning, drinking water resources and carbon cycling between land and sea. Understanding the importance of human activities on TOC changes requires knowledge of past concentrations; however, water-monitoring data are typically only available for the past few decades, if at all. Here, we present a universal model to infer past lake water TOC concentrations in northern lakes across Europe and North America that uses visible-near-infrared (VNIR) spectroscopy on lake sediments. In the orthogonal partial least-squares model, VNIR spectra of surface-sediment samples are calibrated against corresponding surface water TOC concentrations (0.5-41 mg L(-1)) from 345 Arctic to northern temperate lakes in Canada, Greenland, Sweden and Finland. Internal model-cross-validation resulted in a R(2) of 0.57 and a prediction error of 4.4 mg TOC L(-1)...

PloS one, 2017

Recent climate change has been especially pronounced in the High Arctic, however, the responses o... more Recent climate change has been especially pronounced in the High Arctic, however, the responses of aquatic biota, such as diatoms, can be modified by site-specific environmental characteristics. To assess if climate-mediated ice cover changes affect the diatom response to climate, we used paleolimnological techniques to examine shifts in diatom assemblages from ten High Arctic lakes and ponds from Ellesmere Island and nearby Pim Island (Nunavut, Canada). The sites were divided a priori into four groups ("warm", "cool", "cold", and "oasis") based on local elevation and microclimatic differences that result in differing lengths of the ice-free season, as well as about three decades of personal observations. We characterized the species changes as a shift from Condition 1 (i.e. a generally low diversity, predominantly epipelic and epilithic diatom assemblage) to Condition 2 (i.e. a typically more diverse and ecologically complex assemblage with a...

Journal of Limnology, 2015

The tropical Andes are undergoing climate changes that rival those occurring anywhere else on the... more The tropical Andes are undergoing climate changes that rival those occurring anywhere else on the planet, and are likely to have profound consequences for ecosystems. Paleolimnological investigations of remote mountain lakes can provide details of past environmental change, especially where monitoring data are absent. Here, we reconstruct fossil diatom and chironomid communities spanning the last several hundred years from an Andean lake located in an ecological reserve near Quito, Ecuador. Both diatoms and chironomids recorded assemblage shifts reflective of changing climate conditions. The diatoms are likely responding primarily to temperature-related limnological changes, recording an increase in the number of planktonic taxa in the most recent sediments. This change is consistent with warmer conditions that result in enhanced periods of thermal stratification, allowing planktonic species to proliferate. The chironomids appear to respond mainly to a change in precipitation regime...

PLOS ONE, 2015

In the Laurentian Great Lakes region, the double-crested cormorant (Phalacrocorax auritus) has se... more In the Laurentian Great Lakes region, the double-crested cormorant (Phalacrocorax auritus) has seen a thousand-fold population increase in recent decades. These large colonies of birds now often conflict with socioeconomic interests, particularly due to perceived competition with fisheries and the destruction of terrestrial vegetation in nesting habitats. Here we use dated sediment cores from ponds on islands in eastern Lake Ontario that receive waste inputs from dense colonies of cormorants and ring-billed gulls (Larus delawarensis) to chronicle the population rise of these species and assess their long-term ecological impacts. Modern water chemistry sampling from these sites reveals drastically elevated nutrient and major ion concentrations compared to reference ponds not influenced by waterbirds. Geochemical tracers in dated sediment cores, particularly δ 15 N and chlorophyll-a concentrations, track waterbird influences over time. Fossil diatom assemblages were dominated by species tolerant of hyper-eutrophic and polluted systems, which is in marked contrast to assemblages in reference sites. In addition to establishing long-term ecological impacts, this multi-proxy paleoecological approach can be used to determine whether islands of concern have been long-term nesting sites or were only recently colonized by cormorant or ring-billed gull populations across the Great Lakes, facilitating informed management decisions about controversial culling programs.

Science of The Total Environment, 2009

Concentrations and stable isotope ratios of lead (Pb) from lake sediments were used to quantify t... more Concentrations and stable isotope ratios of lead (Pb) from lake sediments were used to quantify temporal patterns of anthropogenic Pb pollution in the Clyde River region of Baffin Island, Arctic Canada. Surface sediments from eight lakes on eastern Baffin Island and one from northern-most Greenland, spanning a gradient of 20°latitude, showed great variability with respect to Pb concentration and stable isotopic Pb ratios, with little apparent latitudinal trend. To constrain the temporal evolution of regional Pb pollution, a well-dated core from one of the sites, Lake CF8 on east-central Baffin Island, was analyzed geochemically at high stratigraphic resolution. A pronounced decrease in the 206 Pb/ 207 Pb ratio occurs in sediments deposited between 1923 and the mid-1970s, likely reflecting alkyl-Pb additives derived from the combustion of fossil fuels at a global scale. A two-component mixing model indicates that 17-26% of the Pb in the labile fraction of sediments deposited in Lake CF8 between 2001 and 2005 is from anthropogenic input. A Pb-Pb co-isotopic plot (206 Pb/ 207 Pb vs. 208 Pb/ 206 Pb ratios) of the Lake CF8 time series data indicates multiple possible sources of industrial Pb pollution. Despite widespread reductions in industrial Pb emissions since the 1970s, there is no evidence for attendant reductions of pollution Pb at Lake CF8. Enhanced scavenging from increased primary production as well as changing precipitation rates as climate warms may represent important factors that modulate Pb deposition to Lake CF8, and Arctic lakes elsewhere.

PLOS ONE, 2015

Air temperatures in the tropical Andes have risen at an accelerated rate relative to the global a... more Air temperatures in the tropical Andes have risen at an accelerated rate relative to the global average over recent decades. However, the effects of climate change on Andean lakes, which are vital to sustaining regional biodiversity and serve as an important water resource to local populations, remain largely unknown. Here, we show that recent climate changes have forced alpine lakes of the equatorial Andes towards new ecological and physical states, in close synchrony to the rapid shrinkage of glaciers regionally. Using dated sediment cores from three lakes in the southern Sierra of Ecuador, we record abrupt increases in the planktonic thalassiosiroid diatom Discostella stelligera from trace abundances to dominance within the phytoplankton. This unprecedented shift occurs against the backdrop of rising temperatures, changing atmospheric pressure fields, and declining wind speeds. Ecological restructuring in these lakes is linked to warming and/or enhanced water column stratification. In contrast to seasonally ice-covered Arctic and temperate alpine counterparts, aquatic production has not increased universally with warming, and has even declined in some lakes, possibly because enhanced thermal stability impedes the recirculation of hypolimnetic nutrients to surface waters. Our results demonstrate that these lakes have already passed important ecological thresholds, with potentially far-reaching consequences for Andean water resources.

Quaternary Science Reviews, 2012

Few lakes in the Arctic preserve sediments older than Holocene age because of pervasive glacial s... more Few lakes in the Arctic preserve sediments older than Holocene age because of pervasive glacial scour during the last ice age. Here we present sediment diatom and geochemical records from a lake on eastcentral Baffin Island (CF8, Nunavut, Canada) that captures three successive interglacial periods within the last 200,000 years: a portion of marine isotope stage (MIS) 7; the last interglacial (MIS 5e); and the Holocene (MIS 1). An additional unit of diatom-rich organic sediment occurs between the latter two intervals, and is ascribed to MIS 5a interstadial conditions. The Lake CF8 paleolimnological record reveals similar ontogenetic trends within each interglacial. Early postglacial environments in both the Holocene and MIS 5e were characterized by a dominance of colonial benthic fragilarioid diatoms that thrived in relatively alkaline waters. These species shifts do not coincide with major changes in base cation delivery to the sediments, suggesting that shifts in diatom assemblages are controlled mainly by climate-driven pH dynamics. Diatom assemblages then transitioned into dominance by tychoplanktonic Aulacoseira species, likely in response to climate-driven pH dynamics. The highest sustained abundances of Aulacoseira occur in sediments ascribed to MIS 5e, and this is the only interval in which thalassiosiroid centric taxa also occur (e.g. Discostella and Puncticulata spp.). Given that these planktonic taxa typically reach high abundances during extended periods of open-water conditions, we surmise that MIS 5e was the warmest interval recorded. The overall similarity of lake ontogenetic trajectories recorded within each interglacial period suggests that climatic and edaphic factors drive a complex succession of environmental changes through indirect effects on lake ice cover, habitat availability, and lake-water pH. In recent decades (past w50 yrs), an unprecedented increase in periphytic Eunotia taxa is evident; these diatoms were only present intermittently during previous glacialeinterglacial cycles. The expansion of Eunotia is attributed to increased habitat availability associated with declining ice cover during recent 20 th century warming. By integrating data from several distinct interglacials, the CF8 diatom record considerably extends our understanding of Arctic lake ontogeny, and provides an unparalleled natural archive with which to compare recent changes associated with anthropogenic climate warming.

Quaternary Research, 2006

A diatom-based paleolimnological investigation was conducted on late Holocene sediments from a po... more A diatom-based paleolimnological investigation was conducted on late Holocene sediments from a poorly buffered lake, informally named “Rock Basin Lake”, on Ellesmere Island, Arctic Canada. The fossil diatom record is unlike any other obtained thus far from high arctic regions, exhibiting dynamic assemblage shifts over the entire ∼3300 yr sedimentary record. Multiple proxies (i.e., diatoms, pH reconstructions, biogenic silica, C/N ratios, total organic carbon) appear to sensitively track rapid limnological changes, which are associated with distinct climate intervals as inferred from other regional proxy records. The highly responsive nature of the diatom assemblages in Rock Basin Lake, relative to those recorded from nearby alkaline sites, appears to be related to this lake's limited ability to buffer changes in pH. The dynamic species responses suggest that the diatoms in Rock Basin Lake are faithfully tracking climatic changes, and that low-alkalinity lakes may provide the mos...

Quaternary Research, 2006

Reconstructions of past environmental changes are critical for understanding the natural variabil... more Reconstructions of past environmental changes are critical for understanding the natural variability of Earth's climate system and for providing a context for present and future global change. Radiocarbon-dated lake sediments from Lake CF3, northeastern Baffin Island, Arctic Canada, are used to reconstruct past environmental conditions over the last 11,200 years. Numerous proxies, including chironomid-inferred July air temperatures, diatom-inferred lakewater pH, and sediment organic matter, reveal a pronounced Holocene thermal maximum as much as 5°C warmer than historic summer temperatures from ∼10,000 to 8500 cal yr B.P. Following rapid cooling ∼8500 cal yr B.P., Lake CF3 proxies indicate cooling through the late Holocene. At many sites in northeastern Canada, the Holocene thermal maximum occurred later than at Lake CF3; this late onset of Holocene warmth is generally attributed to the impacts of the decaying Laurentide Ice Sheet on early Holocene temperatures in northeastern C...

Proceedings of the Royal Society B: Biological Sciences, 2013

We document the rapid transformation of one of the Earth's last remaining Arctic refugia, a c... more We document the rapid transformation of one of the Earth's last remaining Arctic refugia, a change that is being driven by global warming. In stark contrast to the amplified warming observed throughout much of the Arctic, the Hudson Bay Lowlands (HBL) of subarctic Canada has maintained cool temperatures, largely due to the counteracting effects of persistent sea ice. However, since the mid-1990s, climate of the HBL has passed a tipping point, the pace and magnitude of which is exceptional even by Arctic standards, exceeding the range of regional long-term variability. Using high-resolution, palaeolimnological records of algal remains in dated lake sediment cores, we report that, within this short period of intense warming, striking biological changes have occurred in the region's freshwater ecosystems. The delayed and intense warming in this remote region provides a natural observatory for testing ecosystem resilience under a rapidly changing climate, in the absence of direc...

Proceedings of the Royal Society B: Biological Sciences, 2012

Numerous environmental pressures have precipitated long-term population reductions of many insect... more Numerous environmental pressures have precipitated long-term population reductions of many insect species. Population declines in aerially foraging insectivorous birds have also been detected, but the cause remains unknown partly because of a dearth of long-term monitoring data on avian diets. Chimney swifts ( Chaetura pelagica ) are a model aerial insectivore to fill such information gaps because their roosting behaviour makes them easy to sample in large numbers over long time periods. We report a 48-year-long (1944–1992) dietary record for the chimney swift, determined from a well-preserved deposit of guano and egested insect remains in Ontario (Canada). This unique archive of palaeo-environmental data reflecting past chimney swift diets revealed a steep rise in dichlorodiphenyltrichloroethane (DDT) and metabolites, which were correlated with a decrease in Coleoptera remains and an increase in Hemiptera remains, indicating a significant change in chimney swift prey. We argue that...

Proceedings of the Royal Society B: Biological Sciences, 2009

Migratory animals such as seabirds, salmon and whales can transport large quantities of nutrients... more Migratory animals such as seabirds, salmon and whales can transport large quantities of nutrients across ecosystem boundaries, greatly enriching recipient food webs. As many of these animals biomagnify contaminants, they can also focus pollutants at toxic levels. Seabirds arguably represent the most significant biovectors of nutrients and contaminants from the ocean to the land, given their sheer numbers and global distribution. However, long-term census data on seabirds are rare. Using palaeolimnological proxies, we show that a colony of Arctic seabirds has experienced climate-induced population increases in recent decades. We then document increasing concentrations of contaminants, including polychlorinated biphenyls and cadmium, in pond sediments that are linked to biotransport by seabirds. Our findings suggest that climate-related shifts in global seabird populations will have the unexpected consequence of restructuring coastal ecosystems.

Proceedings of the National Academy of Sciences, 2010

Seabirds represent a well documented biological transport pathway of nutrients from the ocean to ... more Seabirds represent a well documented biological transport pathway of nutrients from the ocean to the land by nesting in colonies and providing organic subsidies (feces, carcasses, dropped food) to these sites. We investigated whether seabirds that feed at different trophic levels vary in their potency as biovectors of metals, which can bioaccumulate through the marine foodweb. Our study site, located on a small island in Arctic Canada, contains the unique scenario of two nearby ponds, one of which receives inputs almost exclusively from upper trophic level piscivores (Arctic terns, Sterna paradisaea ) and the other mainly from lower trophic level molluscivores (common eiders, Somateria mollissima ). We used dated sediment cores to compare differences in diatoms, metal concentrations and also stable isotopes of nitrogen (δ 15 N), which reflect trophic position. We show that the seabirds carry species-specific mixtures of metals that are ultimately shunted to their nesting sites. For ...

Proceedings of the National Academy of Sciences, 2009

The Arctic is currently undergoing dramatic environmental transformations, but it remains largely... more The Arctic is currently undergoing dramatic environmental transformations, but it remains largely unknown how these changes compare with long-term natural variability. Here we present a lake sediment sequence from the Canadian Arctic that records warm periods of the past 200,000 years, including the 20th century. This record provides a perspective on recent changes in the Arctic and predates by approximately 80,000 years the oldest stratigraphically intact ice core recovered from the Greenland Ice Sheet. The early Holocene and the warmest part of the Last Interglacial (Marine Isotope Stage or MIS 5e) were the only periods of the past 200,000 years with summer temperatures comparable to or exceeding today's at this site. Paleoecological and geochemical data indicate that the past three interglacial periods were characterized by similar trajectories in temperature, lake biology, and lakewater pH, all of which tracked orbitally-driven solar insolation. In recent decades, however, t...

Limnology and Oceanography, 2011

We studied the effects of four decades of cultural eutrophication on Meretta Lake, in the Canadia... more We studied the effects of four decades of cultural eutrophication on Meretta Lake, in the Canadian High Arctic, through a multiproxy analysis of its sediments, including sedimentary pigments, metal concentrations, stable isotope ratios, chironomids, and diatoms. While Meretta Lake's biota clearly responded to nutrient inputs, the manner in which the changes differed from those expected in temperate lakes underlined the profound effects in Arctic lakes of extended ice and snow cover on light penetration, mixing, and interactions with the atmosphere. Hypolimnetic anoxia developed rapidly in Meretta Lake in response to sewage enrichment and was accompanied by the appearance of photosynthetic sulfur bacteria. Benthic communities responded rapidly to sewage inputs, but phytoplankton biomass did not increase until eutrophication was accompanied by climate warming, further reinforcing the importance of ice cover in controlling biotic processes in high Arctic lakes. With climate-mediated ice cover reductions in Meretta Lake, the response to eutrophication began to more closely resemble temperate processes. Recent trajectories indicate that slightly more than a decade after the cessation of sewage inputs, Meretta Lake is recovering toward pre-enrichment conditions.