The cryosphere is changing rapidly and especially so in mountain and polar regions. These changes are having a myriad of effects on associated freshwater ecosystems and the services they provide to society. A better understanding of these changes, and the mechanisms driving them, will help to protect these ecosystems and to support societal adaptation as climate change unfolds. This session invites submissions from those working from diverse perspectives (biogeochemistry, trophic interactions, water quality, evolutionary adaptation, biodiversity, geomorphology, etc) to better understand ongoing changes in lakes, ponds, streams, and wetlands that are on, adjacent to, or strongly influenced by glaciers, snowpack, and permafrost in mountain regions and at high latitudes. We also invite contributions from researchers studying the ecosystem services (e.g. drinking water, hydropower, fisheries, irrigation) that are impacted in cryosphere-supported freshwater ecosystems. With this session we seek to continue to build a diverse global network of cryosphere limnologists working across disciplinary boundaries.
Lead Organizer: James Elser, University of Montana (jim.elser@umontana.edu)
Co-organizers:
Joseph Vanderwall, University of Montana (joseph.vanderwall@umconnect.umt.edu)
Janice Brahney, Utah State University (jbrahney@gmail.com)
Presentations
06:30 PM
THROUGHFLOW : THE OVERLOOKED COMPONENT OF ALPINE LAKE HEAT FLUXES (6251)
Primary Presenter: Isabel Herr, University of Lausanne (isabel.herr@unil.ch)
Lakes are often described as sentinels for climate change as they integrate changes in global and local climate as well as watershed properties and water transparency. Moreover, alpine lakes respond faster to changes in their catchments than low altitude lakes due to their small size, small catchment areas, and steep surrounding slopes. With accelerated changes in mountain climate, mountain lakes have become of increasing interest to scientists as predictors of changes in low altitude lakes. However, traditional one-dimensional models based solely on meteorologic conditions fail to represent alpine lake temperature cycles reliably. In contrast to low altitude lakes, energy balances in mountain lakes are highly impacted by catchment properties such as snow cover and inflow rather than direct fluxes with the atmosphere. An additional practical challenge comes from the lack of accessibility and harsh field conditions of these lakes. The evolution of mountain lakes in a changing climate is thus still unknown. This study quantifies the role of throughflow in the heat budget in various Alpine lakes in the French alps spanning from 2000 m to 3000 m a.s.l, in glacial and non-glacial watersheds using meteorological and water temperature data collected in the “Reseaux Sentinelle” Lakes in France. Our results highlight that changes in watershed snow cover and spring melt volumes must be included in the classical one-dimensional vertical description of the heat exchanges based on meteorological conditions to characterize the evolution of mountain lakes under climate changes.
06:30 PM
Glacier retreat and increasing vegetation cover alter the sources and sinks of organic and inorganic carbon in alpine streams (4976)
Primary Presenter: Andrew Robison, École Polytechnique Fédérale de Lausanne (andrew.robison@epfl.ch)
High-mountain ecosystems are experiencing acute effects of climate change, most visibly through glacier recession and the greening of the terrestrial environment. The streams draining these landscapes are affected by these shifts, integrating hydrologic, geologic, and biological signals across the catchment. We examined the organic and inorganic carbon dynamics of streams in four Alpine catchments in Switzerland to assess how glacier loss and vegetation expansion are affecting the carbon cycle of these high mountain ecosystems. We find that organic carbon concentration and humic-like fluorescence properties increase with vegetation cover, implying an increasing importance of allochthonous carbon sources following glacier retreat. Meanwhile, streams transitioned from carbon dioxide sinks to sources with decreasing glacier coverage and increased vegetation coverage, with chemical weathering and soil respiration likely determining the balance. Carbon dioxide undersaturation was observed in glaciated and non-glaciated streams, indicating geochemical consumption could be more widespread in high-mountain, minimally vegetated catchments than previously described. Our results demonstrate significant shifts in organic and inorganic carbon dynamics of alpine streams following glacier recession. The clear link between the terrestrial and aquatic zones further emphasizes the coupled dynamics with which all hydrologic and biogeochemical changes in these ecosystems should be considered, including the carbon sink or source potential of montane ecosystems.
06:30 PM
Mountain streams’ role in driving nearshore lake metabolism: a case study of variable flow regimes in the Lake Tahoe Basin, California‐Nevada, USA. (6069)
Primary Presenter: Kelly Loria, University of Nevada Reno (kelly.loria@nevada.unr.edu)
In-stream processes can influence eulittoral zone (nearshore) productivity dynamics through modulating the timing and amount of nutrient delivery to lakes. The degree to which mountain stream processes influence nearshore lake productivity as a function of their seasonal flow regimes remains unclear. To investigate how seasonal variation in stream flow and in-stream metabolic and nitrogen uptake rates covary with nearshore lake productivity, we continuously monitored dissolved oxygen, temperature, stream specific conductance (SPC) and collected surface and pore water samples for nutrient concentrations in streams and around the outlets and the nearshore of Lake Tahoe (California‐Nevada, United States of America), in two watersheds with differing flow regimes. We found that nearshore net ecosystem production (NEP) was negatively correlated with the magnitude of daily streamflow (βflow: -0.618 ± 0.069, p< 0.001, r2c = 0.112) and positively correlated daily SPC (βSPC: 5.64 ± 0.327, p< 0.001, r2c = 0.291). These patterns were particularly pronounced for the west shore of Lake Tahoe which has a greater amount of annual precipitation relative to the drier east shore. The positive and negative relationships between modeled nearshore NEP, SPC and streamflow, suggest that nearshore metabolism may be more related to changes in groundwater inputs relative to surface water. Observed patterns in autotrophic production indicate that precipitation accumulation in mountain watersheds can control the physical stream processes (streamflow, timing of baseflow, and water temperature) which may influence NEP immediately near stream outlets.
06:30 PM
Mountain glaciers strongly influence biogeochemical characteristics of alpine lakes across the northern Rocky Mountains, USA (4635)
Primary Presenter: Joseph Vanderwall, University of Montana (joseph.vanderwall@gmail.com)
Over the past century, the retreat of alpine glaciers across the world has produced thousands of newly formed mountain lakes. These “newborn” lakes receive solute-rich meltwater, yet little is known about their physical (i.e., turbidity from glacial flour) and biogeochemical conditions across a range of glacial influence. We surveyed alpine lakes fed by both glacial and snowpack meltwaters and those fed by snowpack alone to compare nutrient concentrations, stoichiometry, water clarity, chlorophyll, and zooplankton communities across elevational gradients. Total phosphorus and nitrate concentrations were two and three times higher in glacial lakes than in non-glacial lakes, respectively. Despite increased nutrient concentrations, total organic carbon concentrations in glacial lakes were two times lower than in non-glacial lakes, likely due to reduced primary production caused by low water clarity from glacial flour. The carbon to phosphorus ratio and the nitrogen to phosphorus ratio of lake seston increased with water clarity in glacial lakes, suggesting that turbidity from glacial flour increases light limitation and increases stoichiometric food quality for zooplankton in newborn lakes. However, chlorophyll-a concentrations did not differ between lake types. Through piecewise structural equation modeling we found that glaciers exhibit a bidirectional control on nitrate and total phosphorus concentrations mediated through landscape NDVI and lake clarity. In addition, zooplankton communities in high-turbidity glacial lakes comprised cyclopoid copepods and rotifers (i.e., non-filter feeders), while non-glacial lakes tended to be dominated by calanoid copepods and cladocerans (i.e., filter feeders). Our results show that glacier-associated lakes have biogeochemical and ecological characteristics distinct from those in other mountain lakes. Sustained studies are needed to assess the dynamics of these unique features as the influence of the alpine cryosphere fades under ongoing climate change.
06:30 PM
DIVERSITY PATTERNS IN THE PLANKTON COMMUNITIES OF HIGH ALPLINE LAKES IN AN AUSTRIAN PROTECTED AREA: THE EXPECTED AND UNEXPECTED (4898)
Primary Presenter: Stephen Wickham, University of Salzburg (stephen.wickham@plus.ac.at)
High alpine communities are expected to be strongly impacted by climate change, with many of the effects being indirect and modulated by local factors. For the past 6 years we have sampled the zooplankton communities and abiotic parameters of 18 high-alpine lakes in the Hohe Tauern national park in central Austria. The lakes encompass a wide range of size, altitude, maximum depth, age and accessibility. Microclimate is a dominant driver of the annual temperature cycle, with long-term trends only now emerging. Zooplankton communities show high beta diversity, with many species only occurring in a single lake. Both morphological and molecular data show that lakes in close geographic proximity are very different from another, with only water bodies with direct physical connections to one another being similar in their diversity. However, over the period of the study, dissimilarity appears to be declining, at least in terms of zooplankton morphological diversity. There is also evidence that colonization by new species has the potential to have community-level effects. Several of the lakes have deep chlorophyll maxima with at times remarkably high chlorophyll values, albeit with high interannual variability. However, with logistical restraints limiting sampling to one date per year, the degree of intra-annual variability in the chlorophyll and zooplankton data remains unexplored. These data provide a baseline to measure the impending changes in high alpine aquatic communities brought on by climate change.
06:30 PM
TAXONOMY AND FUNCTIONAL POTENTIAL OF PSYCHROPHILIC MICROBES IN THE ICE OF CANADA’S NORTHERNMOST LAKE (6195)
Primary Presenter: Maxime Larose, Université du Québec à Chicoutimi (maxime.larose2@uqac.ca)
High Arctic lake ice was typically perennial, making it a stable habitat for unique microbial psychrophilic organisms. However, warming has disrupted the stability of this unique habitat, as evidenced by the first recorded ice off events that occurred on Ward Hunt Lake (83N) in 2011. Microbial assemblages in perennial lake ice are therefore especially vulnerable to further warming in the Arctic, and since little is known on how lake ice microbes contribute to energy cycling in freshwater systems, it is unclear how they will adapt to variable seasonal ice conditions. Our objective is to describe the microbial assemblages of Ward Hunt Lake ice. Ice cores were collected in July 2022, from which we extracted nucleic acids for next-generation sequencing. Amplicon sequencing of the 16S rRNA gene revealed the presence of a diverse bacterial community including Proteobacteria, Bacteroidota, Actinobacteriota and Cyanobacteria which varied in composition by ice strata, and differed from the underlying water column. Deep shotgun metagenomic sequencing was also used to investigate the functional and metabolic potential of microbes, with special attention to pathways associated with psychrophily, including nutrient utilization (oligotrophy), cold-shock proteins (cold), and genome repair (UV resistance). These data provide a unique portrait of the microbial inhabitants of lake ice in an area subjected to warming conditions and give insight into the metabolic pathways present in the ice, furthering our understanding of the ways in which life in lake ice may change in the future.
06:30 PM
Nutrient requirements of microalgae on the Greenland Ice Sheet revealed by single-cell analyses (6789)
Primary Presenter: Laura Halbach, Aarhus University (lh@envs.au.dk)
Microalgal blooms accelerate the melting of glaciers and ice sheets by lowering the surface albedo. Their growth requirements and direct role in biogeochemical cycling, however, remain elusive. Here, we study the elemental composition and dual assimilation of 13C-bicarbonate and 15N-ammonium or 15N-nitrate in a supraglacial community and single glacier ice algal cells, during in situ incubation experiments on the Greenland Ice Sheet. We observed a rapid uptake and turnover of carbon (C) and nitrogen (N) in the supraglacial community but a lack of stimulation of glacier ice algal productivity after 15N-ammonium, 15N-nitrate, or phosphate additions. This, together with high in situ C:N and C:phosphorus (P) atomic ratios and the ability to store P suggests a lifestyle of the algae highly adapted to the nutrient-poor environment, likely sustaining prolonged growth throughout the season and promoting the potential to colonise new bare ice areas with ongoing climate warming.
SS049P Resilience on Ice: Freshwater Ecosystems and the Changing Cryosphere in Mountain and Polar Regions
Description
Time: 6:30 PM
Date: 8/6/2023
Room: Mezzanine