In the world’s largest deepest lakes, phytoplankton photosynthesis is an important source of new carbon that fuels whole lake productivity. Research by Stephanie Guildford, an Associate Professor at the University of Minnesota-Duluth, focuses on determining rates and controlling factors on primary production (PP) and, importantly, fates of PP.
Great Lakes, especially those with low nutrient concentrations and low phytoplankton biomass, pose extreme logistical challenges. Stephanie and her colleagues use advanced fluorometric instruments to characterize phytoplankton composition and photosynthetic capacity at highly-resolved spatial and temporal scales.
Using data collected from Lake Superior during five cruises in 2010, Stephanie’s lab and colleagues at UMD are studying the deep chlorophyll layer (DCL). In particular, is the DCL light limited, nutrient limited, controlled by grazers, or the sinking of phytoplankton? What links exist between the DCL and the vertical migrating zooplankton Limnocalanus and Mysis? Do these zooplankton feed in the DCL and, if so, how much of their productivity is derived from the DCL? Do the phytoplankton in the DCL use the nutrients excreted by the migrating zooplankton? If so, the connection between the DCL and migrating zooplankton may be an important control point of primary production.