THERMAL STRUCTURE AND OXYGEN DEPLETION PROVIDE MECHANISM FOR CYANOHABS IN LOW NUTRIENT LAKES: CHALLENGING THE EUTROPHICATION-HAB PARADIGM

The management of harmful blooms of cyanobacteria (cyanoHABs) has historically relied on watershed nutrient reduction strategies; however, cyanoHABs have been increasingly reported in remote and oligotrophic lakes whose catchments are relatively protected from human landscape modifications. This has prompted a paradigm shift in our understanding of the drivers of cyanoHABs and a need to study environmental factors beyond watershed nutrient inputs. In this study, we examined eight lakes within the Superior National Forest (Minnesota, USA). We paired high-resolution temperature and dissolved oxygen profiles with monthly measurements of nutrients, algal density, and cyanobacteria community composition to assess the relationship between thermal structure, oxygen depletion rates, and algae, including cyanobacteria. We found that cyanobacteria abundance was correlated to total phosphorus (P) concentrations, which in turn were related to how frequently the lakes experienced “anoximixis”. Anoximixis, which we define as lake turnover with anoxic bottom waters, facilitates the mixing of anaerobically released sediment P to the water column. Taken together, these results suggest that even in our most protected regions, shallow lakes experiencing polymictic thermal regimes may support cyanoHABs through increased internal P loading. As stratification regimes continue to be altered under warmer climate scenarios, improving our understanding of the linkages between cyanoHABs and internal P loading in these remote lakes will allow us to better focus management efforts in the future.

Primary Presenter: Lienne Sethna, St. Croix Watershed Research Station (lsethna@smm.org)

Authors:

Lienne Sethna, St. Croix Watershed Research Station  (lsethna@smm.org)

Amelia Wilson-Jackson, St. Croix Watershed Research Station  (awilson-jackson@smm.org)

Hailey Sauer, St. Croix Watershed Research Station  (hsauer@smm.org)

Alaina Fedie, St. Croix Watershed Research Station  (afedie@smm.org)

Amber White, St. Croix Watershed Research Station  (awhite@smm.org)

Nicole Wagner, Oakland University  (nicolewagner@oakland.edu)

Mark Edlund, St. Croix Watershed Research Station  (medlund@smm.org)

Adam Heathcote, St. Croix Watershed Research Station  (aheathcote@smm.org)