STRATIFICATION INDUCED HARMFUL ALGAL BLOOMS ACROSS A HYPERUEUTROPHIC TO OLIGOTROPHIC GRADIENT

Harmful algal blooms (HABs) are often linked to external nutrient inputs from anthropogenic phosphorus (P) pollution. However, the increasing occurrence of blooms without these inputs has shifted attention to internal drivers. Recent research highlights internal P loading from sediments, driven by changing stratification patterns, as a key trigger. We identify “anoximixis”—the mixing of anoxic bottom waters—as a critical control of internal P loading rates. We present examples from remote, low-nutrient to agriculturally-impacted hypereutrophic lakes, where HABs occur or intensify due to anoximixis. Using high-frequency sensors and traditional monitoring, we compare bloom timing and intensity with factors such as hypolimnetic P accumulation, mixing frequency, and cyanotoxin production. Our findings emphasize the need to characterize anoximixis across regional, morphologic, and trophic gradients as climate change alters lake stratification and bottom water redox conditions. These changes may lead to more toxic blooms in affected systems and trigger blooms in lakes previously thought to be resistant.

Presentation Preference: Oral

Primary Presenter: Adam Heathcote, Science Museum of Minnesota (adam.heathcote@gmail.com)

Authors:

Lienne Sethna, Science Museum of Minnesota  (lsethna@smm.org)

Mark Edlund, Science Museum of Minnesota  (medlund@smm.org)