Biogenic silica concentration as a high-resolution, quantitative temperature proxy at Hallet Lake, south-central Alaska

High-resolution, quantitative temperature records are valuable for placing recent warming in the context of long-term, natural climate variability. Here we use biogenic silica (BSi) concentrations preserved in lacustrine sediment from an oligotrophic lake to quantitatively reconstruct air temperature at Hallet Lake in south-central Alaska. Mean June through August temperature measured over the past 80 yr at Valdez (Alaska) correlate with BSi from Hallet Lake (r=0.87, p=0.01). We chose a nested function to model the non-linear relation between summer temperature and BSi in the calibration data set, and to reconstruct temperature for the past 2 ka. Our BSi-inferred temperature reconstruction shows synchronous changes with independent paleoclimatic proxies for southern Alaska, and provides evidence for a greater rate and magnitude of 20th century temperature warming at Hallet Lake than recorded by other quantitative temperature proxies in the region

Limnological Characteristics Reveal Metal Pollution Legacy in Lakes near Canada’s Northernmost Mine, Little Cornwallis Island, Nunavut

We compared modern limnological characteristics of three lakes near the world’s northernmost base metal (lead-zinc) mine, Polaris Mine, which operated from 1981 to 2002 on Little Cornwallis Island (Nunavut, Canada), to a suite of sites from Resolute Bay (Qausuittuq), Cornwallis Island. Although both study regions are underlain by broadly similar geology and experience nearly identical climatic conditions, present-day water chemistry variables differed markedly between sites on the two islands. Specifically, the lakes near the Polaris Mine recorded substantially higher concentrations of zinc and lead, as well as several other heavy metals (cadmium, molybdenum, nickel, uranium, vanadium), relative to the sites on Cornwallis Island. Although the Polaris Mine closed in 2002, elevated levels of heavy metals in our 2017 survey are likely a legacy of contamination from prior operations. Nous avons comparé les caractéristiques limnologiques modernes de trois lacs situés à proximité de la mine de métaux communs (plomb-zinc) la plus au nord du globe, soit la mine Polaris exploitée de 1981 à 2002 sur la Petite île Cornwallis (Nunavut, Canada), à une série de sites de la baie Resolute (Qausuittuq) sur l’île Cornwallis. Même si les deux régions à l’étude possèdent une géologie grandement similaire et qu’elles connaissent des conditions climatiques quasi identiques, les variables de la composition chimique de l’eau actuelle affichaient des différences considérables entre les sites des deux îles. Plus précisément, les lacs à proximité de la mine Polaris avaient des concentrations de plomb et de zinc nettement supérieures ainsi que plusieurs autres métaux lourds (cadmium, molybdène, nickel, uranium, vanadium) comparativement aux sites de l’île Cornwallis. Même si la mine Polaris a fermé ses portes en 2002, la présence de taux élevés de métaux lourds dans notre levé de 2017 découle vraisemblablement de la contamination émanant d’activités antérieures.&nbsp

Inferring past trends in lake water organic carbon concentrations in northern lakes using sediment spectroscopy

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 R2 of 0.57 and a prediction error of 4.4 mg TOC L-1. First applications to lakes in southern Ontario and Scotland, which are outside of the model’s geographic range, show the model accurately captures monitoring trends, and suggests that TOC dynamics during the 20th century at these sites were primarily driven by changes in atmospheric deposition. Our results demonstrate that the lake-water TOC model has multi-regional applications and is not biased by post-depositional diagenesis, allowing the identification of past TOC variations in northern lakes of Europe and North America over timescales of decades to millennia

A 2200-year record of Andean Condor diet and nest site usage reflects natural and anthropogenic stressors

Understanding how animals respond to large-scale environmental changes is difficult to achieve because monitoring data are rarely available for more than the past few decades, if at all. Here, we demonstrate how a variety of palaeoecological proxies (e.g. isotopes, geochemistry and DNA) from an Andean Condor (Vultur gryphus) guano deposit from Argentina can be used to explore breeding site fidelity and the impacts of environmental changes on avian behaviour. We found that condors used the nesting site since at least approximately 2200 years ago, with an approximately 1000-year nesting frequency slowdown from ca 1650 to 650 years before the present (yr BP). We provide evidence that the nesting slowdown coincided with a period of increased volcanic activity in the nearby Southern Volcanic Zone, which resulted in decreased availability of carrion and deterred scavenging birds. After returning to the nest site ca 650 yr BP, condor diet shifted from the carrion of native species and beached marine animals to the carrion of livestock (e.g. sheep and cattle) and exotic herbivores (e.g. red deer and European hare) introduced by European settlers. Currently, Andean Condors have elevated lead concentrations in their guano compared to the past, which is associated with human persecution linked to the shift in diet.Fil: Duda, Matthew P.. Queen's University; CanadáFil: Grooms, Christopher. Queen's University; CanadáFil: Sympson, Lorenzo. Sociedad Naturalista Andino Patagonica; ArgentinaFil: Blais, Jules M.. University of Ottawa; CanadáFil: Dagodzo, Daniel. University of Ottawa; CanadáFil: Feng, Wenxi. Queen's University; CanadáFil: Hayward, Kristen M.. Queen's University; CanadáFil: Julius, Matthew L.. St. Cloud State University; Estados UnidosFil: Kimpe, Linda E.. University of Ottawa; CanadáFil: Lambertucci, Sergio Agustin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Layton Matthews, Daniel. Queen's University; CanadáFil: Lougheed, Stephen. Queen's University; CanadáFil: Massaferro, Julieta. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Michelutti, Neal. Queen's University; CanadáFil: Pufahl, Peir K.. Queen's University; CanadáFil: Vuletich, April. Queen's University; CanadáFil: Smol, John P.. Queen's University; Canad

A 200-year perspective on alternative stable state theory and lake management from a biomanipulated shallow lake

Abstract. Multiple stressors to a shallow lake ecosystem have the ability to control the relative stability of alternative states (clear, macrophyte-dominated or turbid, algaldominated). As a consequence, the use of remedial biomanipulations to induce trophic cascades and shift a turbid lake to a clear state is often only a temporary solution. Here we show the instability of short-term manipulations in the shallow Lake Christina (Minnesota, USA) is governed by the long-term state following a regime shift in the lake. During the modern, managed period of the lake, three top-down manipulations (fish kills) were undertaken inducing temporary (5-10 years) unstable clear-water states. Paleoecological remains of diatoms, along with proxies of primary production (total chlorophyll a and total organic carbon accumulation rate) and trophic state (total P) from sediment records clearly show a single regime shift in the lake during the early 1950s; following this shift, the functioning of the lake ecosystem is dominated by a persistent turbid state. We find that multiple stressors contributed to the regime shift. First, the lake began to eutrophy (from agricultural land use and/or increased waterfowl populations), leading to a dramatic increase in primary production. Soon after, the construction of a dam in 1936 effectively doubled the depth of the lake, compounded by increases in regional humidity; this resulted in an increase in planktivorous and benthivorous fish reducing phytoplankton grazers. These factors further conspired to increase the stability of a turbid regime during the modern managed period, such that switches to a clear-water state were inherently unstable and the lake consistently returned to a turbid state. We conclude that while top-down manipulations have had measurable impacts on the lake state, they have not been effective in providing a return to an ecosystem similar to the stable historical period. Our work offers an example of a well-studied ecosystem forced by multiple stressors into a new long-term managed period, where manipulated clearwater states are temporary, managed features

High Lake activity

High Lake 210Pb activity from gamma-datin

Plateau Pond 2 broken stick

Plateau Pond 2 plot of broken stick model result

SV8 N2

SV Pond 8 Hill's N2 and Chlorophyll a value

Proteus broken stick

Proteus Lake plot of broken stick model result

West activity

West Lake 210Pb activity from gamma-datin