Phytoplankton responses to nutrients and increased temperature in three Great Lakes regions susceptible to cyanobacterial blooms

There is increased recognition that cyanobacterial blooms occur under diverse environmental circumstances.  In project CYBORG (CYano BlOoms dRivers and Genes) labs from three universities looked at factors driving blooms in Lake Superior, Green Bay, and Lake Erie.  We performed short (2-4 d) nutrient addition assays in comparable ways in the three environments, with a total of 26 such experiments performed across the three lakes over two years. Treatments included adding P, several forms of N (nitrate, ammonium, urea), and incubating under both ambient and at plus 3-degree temperatures.  Using a Fluoroprobe for coarse community resolution, we found that nutrient additions sometimes disfavored greens compared to cyanobacteria, diatoms, and cryptophytes and that warmer temperatures sometimes favored cyanobacteria at the expense of greens. Extracted chlorophyll measurements indicated that elevated temperatures increased growth in all three lakes, but with interactions with nutrients, especially in Green Bay.  Lake Superior was consistently responsive to P and possibly slightly to N whereas both lower lakes responded more variably to P and to different forms of N.  Our work helps to define the diverse limiting factors operating in steering algal communities in bloom-susceptible areas in the Great Lakes. It also shows how networked experimental work can provide insights into environmental variability at a large spatial scale.

Primary Presenter: Robert Sterner, University of Minnesota Duluth (stern007@d.umn.edu)

Authors:

Anjana Adhikari, University of Wisconsin Milwaukee  (adhikar8@uwm.edu)

Sandra Brovold, University of Minnesota Duluth  (brovo001@d.umn.edu)

George Bullerjahn, Bowling Green State  (bullerj@bgsu.edu)

Reane Loiselle, University of Minnesota Duluth  (loise031@d.umn.edu)

Todd Miller, University of Wisconsin Milwaukee  (millertr@uwm.edu)

Ryan Wagner, Bowling Green State  (ryansw@bgsu.edu)