We simulated an experimental summer storm in large-volume (~1200 m3, ~16m depth) enclosures in Lake Stechlin (https://www.lake-lab.de) by mixing deeper water masses from the meta- and hypolimnion into the mixed layer (epilimnion). The mixing included the disturbance of a deep chlorophyll maximum (DCM) which was present at the same time of the experiment in Lake Stechlin and situated in the metalimnion of each enclosure during filling. Phytoplankton community composition and biomass of phytoplankton functional groups were monitored for 42 days after the experimental disturbance event in addition to water physical variables and water chemistry. Mixing disrupted the thermal stratification, increased concentrations of dissolved nutrients and CO2 and changed light conditions in the epilimnion. Mixing stimulated phytoplankton growth and changes phytoplankton community composition, resulting in higher biomass of Cryptophyceae (within one week after mixing), Nostocales (mainly Dolichospermum sp.; 2-3 weeks after mixing) and thereafter Bacillariophyceae (mainly Asterionella sp.).
Empty cells = NAUtermöhl counting on an inverted microscope at 100-1000x magnification, biomass was volumetrically estimated by geometrical approximations (Hillebrand et al. 1999; Utermöhl, 1958; Lund et al., 1958; Hepperle & Schmidt-Halewicz, 2000).Further Project information:Core Facility grant; Award: GE 1775/2-1