Polar inland waters, encompassing Arctic and Antarctic regions, are experiencing unprecedented environmental changes. Warming air temperatures and shifting precipitation patterns are leading to shortened ice durations, novel flow regimes, and altered ecosystem dynamics, affecting the biodiversity and functioning of polar lakes and rivers. This session aims to bring together scientists from diverse disciplines to share their research findings, discuss key issues, and identify future directions for understanding the implications of long-term changes on ecosystem dynamics and hydrological processes in polar environments. Through this multidisciplinary session, we aim to foster collaboration and facilitate the exchange of knowledge among researchers working on various aspects of polar limnology to better understand global change.
Lead Organizer: Hilary Dugan, University of Wisconsin–Madison (hdugan@wisc.edu)
Co-organizers:
Arial Shogren, University of Alabama (ashogren@ua.edu)
Václava (Vendy) Hazuková, University of Maine (vaclava.hazukova@maine.edu)
Presentations
09:00 AM
SPATIAL VARIATIONS IN SUMMER DISSOLVED ORGANIC CARBON CONCENTRATIONS, SOURCES, AND FLUXES ACROSS THE CANNING RIVER WATERSHED IN NORTHEASTERN ALASKA (8099)
Primary Presenter: Craig Connolly, Environmental Protection Agency, Office of Research and Development (connolly.craig@epa.gov)
In northeastern Alaska, rivers drain continuous permafrost watersheds that span from the mountains of the Brooks Range to the coast of the Beaufort Sea, resulting in vegetation, soil organic matter, and hydrologic gradients that can vary between catchments. We studied how these landscape gradients drive spatial variability in concentrations, sources, and fluxes of dissolved organic carbon (DOC) along the Canning River watershed. Water samples were collected from the Canning mainstem and contributing streams from late June to early August 2019-2023, downstream of (i) the Brooks Range headwaters, (ii) the Brooks Range foothills, and (iii) the coastal plain and river delta. We measured DOC concentrations and radiocarbon isotopic composition, and calculated DOC flux using discharge estimates from numerical modeling. River mainstem DOC concentration more than doubled and became younger from the mountains (0.48 mg C L-1; 805 yBP) to the delta (1.4 mg C L-1; 525 yBP). Stream DOC concentrations were highest within the coastal plain (12 mg C L-1) and foothills (3.1 mg C L-1) compared to the mountains (0.48 mg C L-1). Despite making up ~1/3 of the watershed area, the coastal plain and foothills accounted for 42% and 37% of total DOC export. These two physiographic domains disproportionately influence the age and export of summer DOC from the Canning, with implications for coastal biogeochemical cycling and responses to Arctic warming. We hypothesize this is due to strong hydrologic coupling between streams and DOC produced from young, organic-rich, soils during the wet summer months.
09:15 AM
APPLICABILITY OF THE OXYGEN STABLE ISOTOPE METHOD FOR ESTIMATING METABOLISM IN SMALL ARCTIC LAKES (7893)
Primary Presenter: Fredrik Sundberg, Umeå University (fredrik.sundberg@umu.se)
Metabolism is a key property of lake ecosystem functioning, but in remote systems such as Arctic-alpine lakes, metabolism is difficult to estimate due to logistical challenges associated with fieldwork. A method that requires minimal field sampling efforts is the dissolved oxygen (DO) stable isotope (δ18O) approach. However, this method relies on debated assumptions on the dynamics of δ18O relative to DO and lacks evaluation in Arctic-alpine lakes. We evaluated the δ18O method by comparing it to the state-of-the-art free-water diel DO method in 39 small Arctic-alpine lakes during the open water season. We found that whether methods agreed depended on the sampling conditions and lake depth. The methods agreed well in autumn when water temperatures were relatively stable, especially in lakes with fast gas exchange relative to their depth. In these conditions, the impact of metabolism on DO saturation and δ18O is more pronounced relative to temperature-driven changes in DO solubility and the lakes readapt to new steady state conditions faster following changes in mixed layer depth. In contrast, we found low agreement between methods and a frequent occurrence of unrealistic estimates by the isotope method in spring and summer, likely due to solubility decreases that affect DO saturation independent from δ18O. We conclude that the δ18O method can be used in Arctic-alpine lakes if lake characteristics and seasonal climatic conditions are carefully considered.
09:30 AM
Microbial Sentinels: Unveiling Arctic Lake Dynamics and Bioindicators of Climate Change (8196)
Primary Presenter: Emily Hallett, INRS (emily.hallett@inrs.ca)
Lakes are often referred to as sentinels of climate change due to the shifting of physical, chemical, and biological responses occurring throughout their watersheds. Despite the fundamental role of microorganisms in the maintenance of a properly functioning lake ecosystem, microbial community structure and functioning remains poorly understood in the context of a changing Arctic. Additionally, the extent in which microorganisms act as sentinels of environmental changes remains largely overlooked. Here, we aimed to identify an Arctic lake core microbiome to assess its contribution to the overall gene pool; and further characterize select members of this intrinsic community by whole genome sequencing and carbon utilization measurements to assess their response to projected changes in the Arctic. To this end, the genetic content of clear-water Arctic lakes (Bylot Island, NU, Canada) and their surrounding areas (soils, inlets, etc.) was analyzed using high-throughput amplicon sequencing. These analyses revealed non-unique assemblages among the different lakes sampled, leading to the conclusion that innate lake characteristics drive microbial community partitioning in these environments. Moreover, the bacterial isolate studies disclosed specific substrates of interest for enhanced viability, and ongoing genomic analyses will further identify the main metabolic pathways used by these organisms. Since these lakes have low nutrient thresholds, environmental pressures attributed to climate change, such as brownification, can significantly alter internal biotic processes.
09:45 AM
Community-based monitoring reveals responses of aquatic bacterial communities to environmental change around Fort Good Hope and Ts’ude Niline Tuyeta, NT (8404)
Primary Presenter: Jérôme Comte, Institut national de la recherche scientifique (jerome.comte@inrs.ca)
Climate change and associated landscape-level changes are placing severe pressures on northern aquatic resources. In particular, accelerated degradation of permafrost, has led to the drainage or expansion of permafrost lakes and ponds that vary in their nature and characteristics. In parallel, wildfire frequency has increased causing additional pressure on water resources. Across the Sahtú Settlement Area, effects of permafrost thaw and wildfire on aquatic resources are already being observed. It remains unclear, however, how aquatic ecosystems will respond to these environmental changes. As part of a community-based initiative, we performed sampling with the K'ahsho Got'ine Foundation Guardians within Ts'ude Niline Tu'eyeta, a relatively pristine landscape, protected from direct human impacts in the vicinity of Fort Good Hope, NT. We sampled lakes that vary in their geomorphic setting, permafrost conditions and exposure to perturbation in order to validate whether they would also differ on their chemical and biological characteristics. Specifically, we characterized bacterial communities by Illumina sequencing, the dissolved organic matter by its optical characteristics as well as water chemistry. Preliminary results showed that distinct bacterial assemblages were identified among the different lakes, reflecting the local environmental conditions. This project is directly addressing concerns about changes in aquatic ecosystems expressed by community members in Fort Good Hope and will help ensure the capacity of the Guardians to conduct long-term monitoring.
10:00 AM
LONG-TERM TIME SERIES OF SENTINEL PHYTOPLANKTON IN THE MCMURDO DRY VALLEY LAKES, ANTARCTICA (8020)
Primary Presenter: Rachael Morgan-Kiss, Miami Univeristy (morganr2@miamioh.edu)
High-latitude meromictic lakes such as those in the Antarctic McMurdo Dry Valleys (MDV) harbor aquatic ecosystems dominated by the microbial loop. Within this habitat, which is limited year-round by light and nutrients, protists, or single celled eukaryotes, play outsized roles in the food web as the dominant primary producers and the apex predators. Thus, the MDV lake ecosystem represents an ideal system to study the role of sentinel protist taxa in carbon and nutrient cycling. The perennially ice-covered lakes are part of the McMurdo Long Term Ecological Research (McM LTER; mcmlter.org) which curates a three decade dataset of physicochemical and biological parameters. This talk will highlight the biogeography and trophic roles of sentinel protist taxa of MDV lakes. Two decades of data will be synthesized from generated from a chlorophyll a spectral fluorometer (the bbe FluoroProbe), representing annual and long-term trends of three key phytoplankton: an obligate photoautotroph (chlorophytes), and two mixotrophs (haptophytes and cryptophytes). Year-round monitoring has revealed that chlorophytes dominate the summer populations, while mixotrophs are abundant and active during the long, dark polar winter. On the other hand, long-term trends suggest that chlorophytes may be outcompeting other phytoplankton taxa. These changes could have significant impacts on the MDV lake food web.
10:15 AM
EVIDENCE OF CRITICAL SLOWING DOWN AND FLICKERING IN LONG TERM BIOMASS, PRODUCTIVITY AND DIVERSITY TRENDS IN TAYLOR VALLEY LAKES, MCMURDO DRY VALLEYS, ANTARCTICA (8339)
Primary Presenter: Cristina Takacs-Vesbach, University of New Mexico (cvesbach@unm.edu)
While many of the effects that polar regions have been experiencing from decades of warming temperatures and increased thaw have been documented, biological impacts in the McMurdo Dry Valleys, Antarctica have been difficult to discern. The lakes of the McMurdo Dry Valleys provide a unique system in which to study ecosystem responses to climate change. Three decades of intensive study by the McMurdo Long Term Ecological Project has documented physicochemical and biological trends in Taylor Valley Lakes Fryxell, Hoare and Bonney. Subtle climatic changes over the same period, combined with uncoupled dynamics between biomass, productivity and disturbances have made it difficult to distinguish stochastic biological variation from a critical transition that may represent a new state for these lakes. Long term trends in biomass, productivity and microbial diversity [jp1] reveal that Taylor Valley lakes may be approaching a critical biological transition, as evidenced by increased recovery time after disturbance (critical slowing down) and increasing shifts between alternate states (flickering). Such dynamics provide metrics of lake physical or biological stability, enable us to infer the magnitude of disturbance required for a critical state change in the lakes, and predict the impact of future climatic changes on lake biota.
SS29B - Limnology of Polar Environments
Description
Time: 9:00 AM
Date: 5/6/2024
Room: Meeting Room KL