Pigment and Geochemical Markers of Past and Present Cyanobacterial Presence in the Southwestern Lake Superior Region
Lily Karg
University of Minnesota Duluth
Keywords: Biogeochemistry, Cyanobacteria, Paleolimnology, Lake Superior, Pigments, Organic Carbon, High Performance Liquid Chromatography, Elemental Analyzer Isotope Ratio Mass Spectrometry, Sedimentary Organic Matter, Harmful Algal Blooms
Abstract
In the summer of 2012, the oligotrophic waters of Lake Superior experienced the region’s first cyanobacterial bloom along the west shoreline of the Wisconsin Apostle Islands. While cyanobacterial blooms are common in other Laurentian Great Lakes and warmer inland lakes, this was the first event recorded in Lake Superior. In contrast, Siskiwit Lake, WI, which drains into Lake Superior near the bloom location, has reported semi-annual cyanobacterial blooms each summer. This study focused on a more recent 2021 bloom in Siskiwit Lake, along with the sediment deposits in Siskiwit Lake and Siskiwit Bay, near the first 2012 bloom event. Using elemental and isotopic indicators (%OC, %N, and δ13C), and High-Performance Liquid Chromatography (HPLC), the contribution of organic carbon sources over time in these locations was analyzed and compared with the carotenoid and pigment portrait of the 2021 bloom in Siskiwit Lake. Findings suggested that OC sources in the sedimentary record of Siskiwit Bay were primarily lacustrine algae, demonstrating periods of high algal matter productivity, while Siskiwit Lake exhibited higher terrestrial organic matter input in comparison. Furthermore, carotenoid pigments identified in the Siskiwit Lake bloom indicated a large presence of cyanobacteria amongst other algae, corroborating the presence of cyanobacteria paleo-indicators within the sediment. With this data, future investigations of algal pigments in the Lake Superior lacustrine deposits will provide additional reconstruction of high cyanobacteria productivity intervals and identify potential bloom periods in the region's history.
