Bambach, Matthew2020-08-252020-08-252020-02https://hdl.handle.net/11299/215026University of Minnesota M.S. thesis. February 2020. Major: Water Resources Science. Advisor: Andrew Bramburger. 1 computer file (PDF); vi, 84 pages.Cyanobacteria are a diverse and ancient group of phytoplankton that are a normal component of aquatic primary producer communities. They can become a problem when they reach high cell densities and form blooms capable of producing toxins that can threaten human and wildlife populations. These occurrences are referred to as cyanobacterial harmful algal blooms (cHABs). Increasing global cHAB frequency and potency have been attributed to warming temperatures and nutrient over-enrichment, but drivers of local and regional occurrence remain poorly understood. In this thesis, I examined six inland Minnesota lakes with different physical, chemical, and biological attributes to highlight patterns in cyanobacterial dominance of the phytoplankton community and understand which lake attributes were closely related to cHAB activity, with a focus on the cyanotoxin Microcystin, from June to September in 2016 and 2017. Cyanobacteria were found to dominate most study lakes, and visible blooms were observed at southern, central, and northern latitude lakes. Microcystin-producing taxa were observed in all study lakes. July and August were the months most likely to experience cHABs, and 2017 showed increased cHAB activity associated with elevated algal biovolume across systems. Specific drivers of cHABs differed among study lakes, but aggregated data for all lakes suggests that increased cyanobacterial dominance of the phytoplankton, total kjeldahl nitrogen, and chlorophyll-a pigment were the attributes most closely associated with harmful conditions. Finally, different harmfulness metrics to safeguard the public from cHABs are compared to discuss their respective protectiveness.encyanobacterialakesmicrocystinphytoplanktonThesis or Dissertation