Predicting vertical distributions of the harmful algae Microcystis aeruginosa is an important and challenging task. There are complicating factors of various origin (biological and physical) working across time scales (sub-daily to seasonal) and length scales (micrometers to meters). To elucidate the drivers of Microcystis vertical distributions, research has been conducted in three parts: (i) an exploratory field study of Microcystis vertical distributions, (ii) a theoretical model explaining previous observations, and (iii) a targeted field study to calibrate theoretical model parameters. The exploratory field study utilized a long-duration, high-frequency research station in a stratified and eutrophic lake. Using a combination of dimensional analyses and machine learning techniques, results indicated that subsurface Microcystis concentration peak magnitude and location were significantly mediated by lake thermal structure. A novel theoretical model to explain these observations was subsequently derived, coupling lake hydrodynamics with Microcystis motility and colony dynamics in a one-dimensional advection-dispersion-aggregation model. Results demonstrated vertical transport is highly dependent on Microcystis colony size, which is in turn dependent on wind-induced mixing. To calibrate the theoretical model, a field study is underway to relate wind intensity to Microcystis vertical transport and colony formation rates. The iterative nature of this work—from data to theory and back again—will also be discussed in a broader context of ecological modeling.

Primary Presenter: Jackie Opfer, Augustana College (jackieopfer@augustana.edu)

Authors:

Jackie Opfer, Augustana College  (jackieopfer@augustana.edu)

Carme Calderer, University of Minnesota, Twin Cities -- Department of Mathematics  (calde014@umn.edu)

Miki Hondzo, University of Minnesota, Twin Cities -- Department of Civil, Environmental, and Geo Engineering  (mhondzo@umn.edu)

Vaughan Voller, University of Minnesota, Twin Cities -- Department of Civil, Environmental, and Geo Engineering  (volle001@umn.edu)