A first assessment of cyanobacterial blooms in oligotrophic Lake Superior

Abstract

Lake Superior is often described as the most pristine of the Laurentian Great Lakes, but in the past decade Dolichospermum blooms have been observed. Land use in the adjacent watershed has not changed appreciably during this time, but the lake is warming and climatological variables correspond with presence of blooms. Blooms occurred only in relatively warm years as measured by degree days. Furthermore, the two largest blooms, in 2012 and 2018, occurred during years of especially extreme rainfall, providing coincidental evidence that intense storms provide nutrients or living propagules to the blooms from the watershed. Nearshore lake water in the narrow zone where blooms appear shows some riverine influence compared to water further offshore even in the absence of blooms. Nevertheless, water chemistry associated with the largest bloom in 2018 more closely resembled nonbloom nearshore lake water than river water, suggesting that blooms develop or at least persist outside of distinct river plumes. Concentrations of P and N during peak bloom density greatly exceeded any nonbloom lake or river waters, indicating that a buildup of phytoplankton biomass perhaps by floating and drifting to shore also is a significant factor in bloom occurrence. One potentially toxic substance (Anabaenopeptin A) was observed but at low concentration. At peak phytoplankton concentration, high seston C : P indicated severe P limitation while low C : N pointed against N limitation. If these newly observed blooms are indeed driven by temperature and rainfall as this evidence suggests, blooms may continue. Cyanobacterial blooms (defined as "a massive accumulation of cyanobacterial biomass, formed through growth, migration, and physical-chemical forces"; Tromas et al. 2017) are a significant and increasingly prevalent global water quality problem (Paerl and Otten 2013; Ho et al. 2019). Blooms of cyanobacteria are most often associated with eutrophic or

Cyanobacterial blooms in oligotrophic lakes: Shifting the high‐nutrient paradigm

“…In the absence of mixing, buoyant cyanobacteria float upwards, forming surface blooms. These can accumulate on the shore, forming scums, even in oligotrophic lakes with low overall cyanobacterial biomass (Carey, Ibelings, et al, 2012; Sterner et al., 2020). Surface bloom formation may enhance access to carbon dioxide (CO 2 ) from the atmosphere (Paerl & Ustach, 1982; Visser et al., 2016); however, complete inorganic carbon (C) depletion in scums can still occur, caused by the high biomass and local C demand (Ibelings & Maberly, 1998).…”

“…Rigosi et al (2014) analysed more than 1,000 lakes in the contiguous U.S.A. and found that oligotrophic lakes were more susceptible to increases in the relative abundance of cyanobacteria from increased nutrients alone, while mesotrophic lakes were more impacted by temperature, and eutrophic lakes were most affected by the concomitant effects of nutrients and temperature. An increased frequency in major precipitation events and associated run-off events provides sporadic inputs of limiting nutrients to oligotrophic systems (Jeppesen et al, 2009;Sterner et al, 2020), which may be used directly or stored by cyanobacteria for later use. Nõges et al (2011) found that chlorophyll increased in an oligotrophic lake following a rainy winter period, while cyanobacterial blooms were disrupted in a nearby eutrophic lake due a change in phytoplankton community composition toward a higher abundance of diatoms, chlorophytes, and chrysophytes.…”

“…A central theme to this body of work is that blooms are caused by anthropogenic eutrophication (Dokulil & Teubner, 2000; Lürling et al., 2018). While there is a wealth of evidence that high nutrient loads promote cyanobacterial blooms, there is also widespread evidence that blooms occur in oligotrophic systems (Callieri et al., 2014; Carey, Ewing, et al, 2012; Carey et al., 2014; LeBlanc et al., 2008; Molot et al., 2021; Salmaso et al., 2015; Sterner et al., 2020; Winter et al., 2011), and that they are not a recent phenomenon (Ewing et al., 2020). Some metalimnetic bloom‐forming cyanobacteria, such as Planktothrix rubescens in Lake Bourget France, Switzerland, even appeared in a context of strong re‐oligotrophication because of increased light availability in the metalimnion (Jacquet et al., 2005).…”

Bioactive Metabolites Produced by Cyanobacteria for Growth Adaptation and Their Pharmacological Properties

“…Chroococcidiopsis-like cyanobacterium [14] Halophilic Hypersaline lakes, coastal hypersaline lagoons, saline springs, salt flats and ponds Synechococcus sp., Leptolyngbya sp, Nodosilinea sp., and Geitlerinema sp [15] Oligotrophics Coastal regions of marine and freshwater Dolichospermum lemmermanii [16,17] Psychrophilic Alpines and polar regions Nostoc sp., Leptolyngba sp., Oscillatoria sp. and Phormidium sp.…”

Modeling of the large-scale nutrient biogeochemical cycles in Lake Onego

“…9 a). For example, explanations for the ongoing eutrophication and emergent cyanobacteria blooms in large boreal lakes, such as Lake Winnipeg and Lake Superior, are sought in the immediate effects of 395 changing external inputs and impacts rather than in the evolution of internal biogeochemical cycling (e.g., Schindler et al, 2012;Zhang and Rao, 2012;Bunting et al, 2016;Sterner et al, 2020;Howarth et al, 2021).…”