Lakes, rivers and streams in northern boreal and arctic regions are subject to ongoing changes in water distribution and availability, organic and inorganic chemical loading and processing, and ecosystem structure and composition in response to changing climatic and landscape conditions. Multiple drivers of change include (but are not limited to) warmer temperatures, permafrost thaw, and extended ice-free seasons; altered precipitation and hydrology; and changing flora, fauna, wildfire, and land use. Circumboreal and panarctic understanding of ongoing and projected change in aquatic systems requires detailed process information collected at representative locations, as well as the ability to scale that information spatially across vast unmeasured areas and forward through time. Hence, there is a need to integrate quantitative process-study results and long-term monitoring data with spatially explicit synoptic and remotely sensed information in order to project future conditions. This session welcomes presentations that integrate current and past measurements of aquatic ecosystems with spatial and temporal drivers of change to improve broad scale understanding of current conditions and future trajectories of change in northern inland waters. Related topics include terrestrial release and aquatic biogeochemical processing of carbon, nutrients, suspended solids, and toxins; change in water and materials exports to receiving waters and coastal areas; burial in sediments and atmospheric gas exchange; change inland water surface area and distribution; and change in aquatic community structure and dynamics.
Lead Organizer: Robert Striegl, US Geological Survey, Water Mission Area, Earth System Processes Divsion, Boulder, Colorado, USA (robstriegl@gmail.com)
Co-organizers:
Suzanne Tank, Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada (suzanne.tank@ualberta.ca)
Jan Karlsson, Climate Impacts Research Centre (CIRC), Department of Ecology and Environmental Science, Umeå University, 901 87 Umeå, Sweden (jan.p.karlsson@umu.se)
Presentations
10:30 AM
LINKING CHEMICAL DIVERSITY AND DEGRADATION OF DISSOLVED ORGANIC MATTER WITH CHANGING LANDSCAPE FEATURES IN ARCTIC FRESHWATERS (6690)
Tutorial/Invited: Invited
Primary Presenter: Núria Catalán, IDAEA-CSIC (ncatalangarcia@gmail.com)
Global change is strongly impacting Arctic freshwaters, integrated in a landscape that is quickly warming, undergoing significant changes in hydrological processes and permafrost thaw. All these changes are impacting soil organic matter cycling as well as hydrologic export from soils to adjacent streams and lakes as particulate and dissolved organic matter (DOM). As export and sources change, DOM is also expected to change, both in its chemical diversity and reactivity. DOM chemical diversity defines its availability for the microbial community and thus, ultimately the C export to the Arctic Ocean. Here, we evaluate how changes in landscape controls such as in hydrological connectivity and rock-weathering may impact DOM composition, stability and degradation. Our results include the evaluation of indices describing DOM chemical diversity as predictors of DOM degradation, the link between the distribution of such diversity across water bodies (including both streams and lakes/ponds) and its relation with landscape setting. These results provide valuable information and foster discussions on different approaches to enhance mechanistic understanding and assess biogeochemical responses of Arctic water bodies to climate change on a landscape scale.
10:45 AM
MICROBIAL CARBON PROCESSING IN ICE-WEDGE POLYGONAL TUNDRA PONDS: INFLUENCE OF DOM QUALITY AND NUTRIENT AVAILABILITY (5237)
Primary Presenter: Thomas Pacoureau, Institut national de la recherche scientifique (thomas.pacoureau@gmail.com)
Climate change can promote the expansion of the global area occupied by ponds in ice-wedge polygon landscapes. Concurrently, organic material previously sequestered in permafrost becomes accessible to microbial degradation. We aim to identify the drivers of dissolved organic matter (DOM) transformation in these small aquatic systems in order to better understand carbon cycling in Arctic lowlands. During summers 2017 to 2019, ponds displaying different levels of permafrost erosion and colonization by primary producers were sampled in a glacier valley on Bylot Island (Nunavut, Canada). We assessed spatial variations in DOM concentration, absorbance and fluorescence (PARAFAC modelling), and in the speciation of nutrients. Filtered water from 15 ponds was incubated over 180 days in the dark and we quantified the loss of dissolved organic carbon (DOC) over time, with a subset of samples enriched with nutrients. Different aspects of bacterial metabolism were also measured along with environmental conditions. The results show that despite differences in DOM and nutrient availability, DOC decline was similar among ponds; about 30% of DOC was consumed. However, nutrient addition doubled the rate of DOC decomposition in ponds characterized by high permafrost erosion. Hypoxic bottom water layers were also identified as hot spots for the microbial transformation of DOM. A better understanding of DOM processing in these abundant water bodies is key to assess future trends in lateral carbon export along the terrestrial-aquatic continuum in the Arctic, and its impact on futur climate.
11:00 AM
EARLIER ICE-OUT CAN LEAD TO INCREASING HYPOLIMNETIC OXYGEN CONCENTRATIONS DESPITE HIGHER LAKEWATER TEMPERATURES IN SMALL ARCTIC LAKES IN WEST GREENLAND (4639)
Primary Presenter: Vaclava Hazukova, University of Maine (vaclava.hazukova@maine.edu)
While trends toward earlier ice-out have been documented globally, the links between ice-out timing and lake thermal and biogeochemical structure remain unclear, especially in high-latitude lakes where ice-out occurs close to summer solstice and spring mixing tends to be very short. Using a unique, long-term dataset of vertical profiles and high-frequency data collected intermittently over the past 20 years from 15 oligotrophic lakes located near Kangerlussuaq in West Greenland, we investigate how changing ice-out and weather conditions affect lake thermal structure and hypolimnetic oxygen concentrations. Ice-out timing and weather conditions immediately following ice-out have a decisive impact on temperatures in hypolimnion, with the highest hypolimnetic temperatures (~13ºC) occurring during years when early ice-out is coupled with cooler air temperatures, and the lowest (~4ºC) in years when late ice-out and higher air temperatures prevent full spring mixing in some lakes. We also found that warmer hypolimnion is associated with less hypoxia. This unexpected correlation is a result of higher potential for a substantive spring mixing in years with early ice-out. By affecting the variability of spring mixing occurrence and duration, shifts in ice phenology can have unexpected consequences for lakes at high latitudes that differ from expectations based on temperate regions.
11:15 AM
Inter-regional geomorphological drivers of DOC dominance in postfire boreal lake carbon dynamics (6235)
Primary Presenter: Mathilde Belair, Universite de Montreal (mathilde.belair@umontreal.ca)
Wildfires' intensity and frequency have increased across northern landscapes, disrupting carbon cycling and transport across terrestrial-aquatic ecosystems. However, it remains unclear how lake carbon dynamics respond to fires due to the lack of studies including both spatial and temporal gradients. We analyzed the concentration and distribution of C-species (DOC, DIC, POC, CO2, CH4,) in 56 lakes in burnt vs control catchments in 3 boreal regions of Quebec and Minnesota with a 3-year post-fire gradient. Overall, lakes were more similar within than among regions regardless of fire, but there were intra-regional fire effects. DOC increased in lakes in burnt watersheds, and surface water oxygen concentrations were typically lower in burnt vs control watersheds despite no significant effect on concentrations of CO2 and CH4. In addition, wildfires increase the contribution of DOC to whole-lake C budgets favouring reduction of water transparency and greater opportunity for in-situ carbon processing through mineralization. This lake C dynamic change through an increased quantity and proportion of DOC suggests a potential long-term fire mediated carbon export with a yet undetermined fate in boreal watersheds. Through the integration of various C species with different turnover rates and fates this study highlights a potential longer-term fire-effect on C cycling at the watershed scale with possible implication on global C cycling.
11:30 AM
CHANGES IN AQUATIC CARBON FOLLOWING RESTORATION OF A BOREAL WETLAND IN NORTHERN SWEDEN (5117)
Primary Presenter: Marcus Wallin, Swedish University of Agricultural Sciences (marcus.wallin@slu.se)
To restore drained wetlands by raising the groundwater table has been suggested as an efficient measure to reduce degradation of peat soils and in turn decrease atmospheric CO2 emissions. Such restoration efforts are already being widely conducted across Sweden and the plan is to continue at large scales. However, limited information exists regarding the effects of restoration on lateral export of carbon (C) via the aquatic pathway. Any changes in the lateral C flux are critical to consider as it affects the overall wetland carbon balance and may offset any climatic benefits from the restoration. In addition to the carbon balance perspective, changes in the aquatic C export could affect downstream surface water quality. In this study, we monitored aquatic C (DOC, DIC and CH4) in two streams draining a boreal wetland that was rewetted during autumn 2020. By comparing pre- (2018-2020) and post- (2020-2022) restoration periods we were able to detect any changes in the aquatic C pool. The results showed that the restoration effect was site-, season- and carbon component-specific. One of the stream sites showed no effect of the restoration on aquatic C, whereas the other site showed overall elevated (DOC) or highly elevated (CH4) concentrations post restoration. For DOC, the increase mainly occurred during autumn and winter, whereas increased CH4 concentrations were visible at all seasons. These results are fundamental when evaluating the environmental benefits of rewetting formerly drained wetlands.
11:45 AM
THE NET CARBON FOOTPRINT OF A BOREAL HYDROELECTRIC RESERVOIR OVER THE FIRST FOUR YEARS AFTER FLOODING (6129)
Primary Presenter: Paul del Giorgio, Univ. du Quebec a Montreal (del_giorgio.paul@uqam.ca)
There is still much uncertainty concerning the magnitude of greenhouse gas (GHG) emissions attributable to reservoirs. This uncertainty results from a lack of clear accounting methodologies to determine pre- and post-flood GHG balances (i.e. net carbon footprint), incomplete accounting of all major emission pathways (i.e., diffusion, ebullition, degassing), and insufficient understanding of the spatio-temporal variability of these emissions. Here we present the net carbon footprint for the newly created La Romaine 2 reservoir (RO2), located in Eastern Canada. We sampled RO2 intensively over the first 4 years after flooding. The pre-flood GHG balance was estimated via landscape modeling. For the post-flood GHG balance, we modeled CO2 and CH4 surface water concentrations based on field data to create a grid across the whole reservoir to incorporate spatio-temporal variability and overlayed this grid with spatially explicit gas transfer velocities to calculate diffusive fluxes. Measured ebullition fluxes were propagated over the grid based on depth and temperature, and outflow degassing was estimated based on continuous CO2 and CH4 measurements and water discharge at the turbine. Here we describe the evolution of the C footprint and of its components over the first four years of flooding, and conclude that the net C emissions relative to generating capacity are low compared to other reservoirs that have been studied, due to the particular reservoir configuration. The framework applied here can be transposed to other reservoirs for more robust accounting of their C footprints.
SS021B Responses of Boreal and Arctic Inland Waters to Changing Climatic and Landscape Conditions
Description
Time: 10:30 AM
Date: 7/6/2023
Room: Sala Menorca B