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. Primary production rates as well as exoenzyme activities (alkaline phosphatase, beta-glucosidase, leucine aminopeptidase) were monitored for 42 days after the experimental disturbance event by incubation of size-fractionated sample with H14CO3- and MUF substrate analogue assays, respectively. Mixing disrupted the thermal stratification, increased concentrations of dissolved nutrients and CO2 and changed light conditions in the epilimnion. Thus, mixing stimulated phytoplankton production, resulting in higher primary production rates within one week after mixing.

Further Project information:Core Facility grant; Award: GE 1775/2-1