Historical landscape management, an increase in ignitions, and climate change have led to an increase in wildfires globally. Wildfires are expected to increase in size, frequency and severity as global temperature increases. Direct effects from wildfires can affect fundamental hydrologic and biogeochemical transformations from land to water (e.g., groundwater, lakes, streams) while smoke plume emissions from fires can alter the ecology of ecosystems far beyond burned watersheds. This session will focus on understanding wildfire impacts on aquatic ecosystems at different scales of time (seasonal to decadal) and space (single ecosystems to continental and global). We will also consider impacts across biological scales, from physiological impacts on organisms to biogeochemical cycling. We seek to unravel how wildfires affect fundamental functional processes within aquatic ecosystems and to understand the resilience of ecosystems to wildfire disturbances. Simply, in this session we will explore what happens when fire and water mix?

Lead Organizer: Sudeep Chandra, University of Nevada- Reno (sudeep@unr.edu)

Co-organizers:

Facundo Scordo, Instituto Argentino de Oceanografía, Universidad Nacional del Sur (UNS)-CONICET, Bahía Blanca, Buenos Aires, Argentina (scordo@agro.uba.ar)

Adriane Smits, UC Davis (adriannesmits@gmail.com)

Jessica Corman, Unviersity of Nebraska, Lincoln (jcorman3@unl.edu)

Janice Brahney Brahney, Utah State University (janice.brahney@usu.edu)

Steve Sadro, UC Davis (ssadro@ucdavis.edu)

Presentations

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05:30 PM

WILDFIRES SHIFT PRIMARY PRODUCTIVITY TOWARDS LIGHT LIMITATION IN FORESTED LAKES OF THE UPPER GREAT LAKES REGION (7859)

Primary Presenter: Eva Hendrickson, University of Minnesota - Duluth (hendr786@d.umn.edu)

Wildfires are becoming larger, more frequent, and more severe across the U.S., including the Upper Great Lakes region, where they pose an increasing threat to remote, forested lakes. Previous studies on lake responses to wildfires have documented diverse water quality results, but it is unclear how resource limitation of phytoplankton is impacted. We studied monthly water quality responses of 30 lakes (15 burned, 15 control) affected by the 2021 Greenwood Fire (northeastern MN) one-year post-fire to understand the impact of wildfires on resource limitation in lake ecosystems. We hypothesized that burned lakes with increased dissolved organic carbon (DOC) and total suspended solids (TSS) would lead to reduced water clarity and potentially induce light limitation, as increased nutrient availability would temporarily lessen nutrient limitation. Findings have shown increased total phosphorus (TP), total nitrogen (TN), DOC, TSS, and decreased water transparency in burned versus control lakes, but phytoplankton biomass (chlorophyll a) did not differ. Despite increased nutrient availability in burned lakes, decreased water clarity and no difference in chlorophyll a suggests that phytoplankton communities became increasingly light limited following the wildfire. Our findings suggest that changing wildfire regimes in Minnesota may result in brownification of pristine lakes, and potentially shift phytoplankton communities towards functional traits to overcome light limitation, such as buoyancy-controlling cyanobacteria.

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05:30 PM

INVESTIGATING LAKE ECOSYSTEM RESPONSE TO INCREASED TEMPERATURE AND WILDFIRE OCCURRENCE (8138)

Primary Presenter: Kevin Ng, University of Western Ontario (kng342@uwo.ca)

Air temperatures in the boreal forest have increased about twice that of the global average and are contributing to increases in the frequency and intensity of wildfires. How these changes will impact lakes in the boreal region remains unclear. In this study we use paleolimnological methods to determine the impacts of warming and wildfire on six boreal lakes located near Yellowknife, Canada. The lakes were selected to help determine factors affecting lake resiliency, and include deep (>5 m) and shallow (<3 m) lakes, with recent (<5 yrs prior to sediment retrieval) and historically (>20 yrs ago) burned catchments. Based on ²¹⁰Pb and ¹⁴C dating, the sediment records span the past ~500 to ~1200 years. To investigate the effects of warming and wildfire on lakes, we measured sedimentary chlorophyll-a, biogenic silica, and stable C and N isotopes, inferred past lake-water TOC, and identified diatom community composition. Cluster and rate of change analysis and generalized additive models were used to identify significant changes in the diatom community composition and timing of change in the other proxies, respectively. No long-term changes were linked to wildfire, even in lakes with severely burned catchments, but were linked to the onset of rapid warming. Changes in shallow lakes were much more pronounced than in deep lakes, highlighting the sensitivity of shallow, boreal lakes to rising temperatures. Our findings show with warmer temperatures, shallow boreal lakes will increase in primary production with the potential for irreversible regime shifts in these aquatic ecosystems.

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