Phytoplankton Iron Nutrient Limitation within Lake Superior's Watershed: Investigating Oligotrophic Algal Blooms from a Land to Lake Gradient

Recent impacts of the global climate crisis, coupled with anthropogenic eutrophication, have amplified the magnitude and frequency of Cyanobacterial Harmful Algal Blooms (cHABs) globally. The relatively pristine, cold, and oligotrophic Lake Superior, while typically considered an environment resistant to cHAB forming conditions, has begun to develop blooms along its southwest shore. While trace metal limitation has been broadly explored in marine settings, freshwater studies into micronutrient limitation are comparatively rare. This study investigates how iron limitation impacts algal communities in a land to lake transect on the south shore of Lake Superior. We performed five day, trace metal clean, nutrient addition bioassays with an iron chelator (EDTA), phosphorus, and iron treatments on whole water samples to measure growth differences among sites and treatments. We also extracted and sequenced RNA from a subset of bioassay bottles to identify community differential gene expression responses to the nutrient additions. This research reveals how trace iron concentrations affect primary producers along an inland lake to river to Lake Superior gradient in a location subject to cHABs.

Primary Presenter: Robert McManus, University of Minnesota - Duluth (mcman247@d.umn.edu)

Authors:

Robert Sterner, University of Minnesota - Duluth  (stern007@d.umn.edu)

Cara Santelli, University of Minnesota  (santelli@umn.edu)