LIGHT AND NUTRIENT LIMITATION OF ICE-ASSOCIATED AND PLANKTONIC PHOTOAUTOTROPHS

Phytoplankton abundance under-ice is often lower than in the ice-free season but in eutrophic lakes primary producer biomass may remain elevated in the winter. Under-ice primary producers also have access to additional habitat in the form of the ice itself. Phytoplankton communities can vary due to light intensity and under-ice habitats. Despite high dissolved nutrients and lower light intensity under ice, winter primary producers can still exhibit nitrogen and phosphorus limitation in addition to light limitation. Diatoms are often important primary producers in winter and may experience silica-limitation. The goal of our study is to compare light and nutrient limitations of ice-associated and planktonic photoautotrophs. in a hypereutrophic reservoir. We conducted a 14-day under-ice experiment by deploying nutrient-diffusing substrates at the ice-water interface (ice-associated) and phytoplankton bags (planktonic). Both were amended with nitrogen (N), phosphorus (P), silica (Si), and N+P+Si nutrients. The light was manipulated by removing snow (high light) or leaving the snow (low light). Phytoplankton were light limited and ice-associated photoautotrophs were light inhibited. Phytoplankton were P-limited in low light treatments and not-limited in high light while ice-associated photoautotrophs were silica-limited in high light treatments. This study affirms that nutrient limitation and light limitation co-occur under ice and suggests differential light responses by planktonic and ice-associated photoautotrophs.

Primary Presenter: Hong An Nguyen, Univerisity of Wisconsin - Stout (nguyenh8759@my.uwstout.edu)

Authors:

Hong An Nguyen, University of Wisconsin-Stout  (nguyenh8759@my.uwstout.edu)

Lesley Knoll, Miami University  (knolllb@miamioh.edu)

Nicole Hayes, University of Wisconsin-Stout  (hayesn@uwstout.edu)