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. Water physical variables and water chemistry 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. Mixing stimulated phytoplankton growth, thus, resulting in a bloom of Dolichospermum sp. and thereafter increased biomass of Bacillariophyceae. Subsequent, break down of both phytoplankton groups resulted in higher particulate matter sinking fluxes of particulate organic carbon (POC), total particulate nitrogen (TPN) and total particulate phosphorous (TPP) 4-5 weeks after the disturbance event. Mixing resulted in average increases in elemental downward fluxes of 9% POC, 14% total particulate Nitrogen (TPN) and 19% TPP by the end of the experiment (42 days) (n.control=4, n.mixed=4).
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.).
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.