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. Size-fractionated (0.2-3 µm and >3.0 µm) chlorophyll a (Chla) development was monitored for 42 days after the experimental disturbance event. Mixing disrupted the thermal stratification, increased concentrations of dissolved nutrients and CO2 and changed light conditions in the epilimnion. Thereby, mixing increased the concentration of Chla of the small size fraction 0.2-3.0 within one week after mixing. After 2-3 weeks, mixing resulted in increased concentrations of Chla also in the large size fraction, which was associated to a bloom of Dolichospermums sp.

Principal Investigators for Chlorophyll a = Berger, Stella; Nejstgaard, Jens; Gessner, MarkFurther Project information: Core Facility grant; Award: GE 1775/2-1