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

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.

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

Authors:

Eva Hendrickson, University of Minnesota Duluth, Natural Resources Research Institute, Duluth, MN USA  (hendr786@d.umn.edu)

Jerry Henneck, University of Minnesota Duluth, Natural Resources Research Institute, Duluth, MN USA  (jhenneck@d.umn.edu)

Ian McCullough, Michigan State University, Department of Fisheries and Wildlife, East Lansing, MI USA  (immccull@gmail.com)

Jennifer Brentrup, Minnesota Pollution Control Agency, St. Paul, MN USA  (jennifer.brentrup@state.mn.us)

Christopher Filstrup, University of Minnesota Duluth, Natural Resources Research Institute, Duluth, MN USA  (filstrup@d.umn.edu)