PIGMENT BIOMARKERS OF HISTORIC CYANOBACTERIAL PRESENCE IN THE SOUTHWESTERN LAKE SUPERIOR REGION

Since the first documentation in 2012, cyanobacteria blooms in Lake Superior have raised concerns regarding the health of the lake. To address whether these blooms are a new phenomenon, a series of sediment cores were collected from Siskiwit Bay on Lake Superior’s Wisconsin shoreline. Elemental (%OC and %N), isotopic (δ¹³C), and molecular (algal pigments) signatures were used to reconstruct historical profiles of productivity and bloom periods. Carotenoid pigments were extracted from water samples collected during a nearby bloom to develop a pigment profile for cyanobacterial blooms in Lake Superior and tracked downcore in the Siskiwit Bay core samples. Overall algal productivity, measured via the sum of chlorophyll and carotenoid pigments, has significantly increased towards the present day. Diatom-associated pigments have been in higher concentrations than cyanobacteria pigments since 170 cal year BP, aligning with previous studies indicating that diatoms are currently the dominating phytoplankton species in Lake Superior. Despite diatom community dominance, peaks in cyanobacteria-associated pigments correlate with the 2012 bloom and likely an earlier bloom around 470 cal year BP. As the first study of sedimentary pigments within the southwestern region of Lake Superior, this work provides historical context that informs our understanding of modern-day cyanobacteria presence.

Primary Presenter: Lily Karg, University of Minnesota Duluth (karg0038@d.umn.edu)

Authors:

Jordan Bremer, Large Lakes Observatory, University of Minnesota Duluth, Duluth, MN  (breme185@d.umn.edu)

Lily Karg, Large Lakes Observatory, University of Minnesota Duluth, Duluth, MN  (karg0038@d.umn.edu)

Kathryn Schreiner, Large Lakes Observatory, University of Minnesota Duluth, Duluth, MN  (kschrein@d.umn.edu)

Byron Steinman, Department of Earth and Environmental Sciences, University of Minnesota Duluth, Duluth, MN  (bsteinma@d.umn.edu)

Joseph Carlin, Department of Geological Sciences, California State University Fullerton, Fullerton, CA  (jcarlin@fullerton.edu)

Robert Sterner, Department of Biology, University of Minnesota Duluth, Duluth, MN  (stern007@d.umn.edu)

Hilary Dugan, Center for Limnology, University of Wisconsin-Madison, Madison, WI  (hdugan@wisc.edu)