TemBi 2014 mesocosm study: Summer storm effect on chlorophyll a development in Lake Stechlin@en

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.本研究在施特希林湖（Lake Stechlin，https://www.lake-lab.de）的原位围隔（体积约1200 m³，水深约16 m）中开展夏季风暴模拟实验，通过将斜温层（metalimnion，简称meta层）与湖下层（hypolimnion）的深层水体混合至混合层（epilimnion，湖上层）。此次混合过程扰动了实验期间施特希林湖原位存在的叶绿素最大值层（deep chlorophyll maximum, DCM），该层在围隔注水阶段位于各围隔的斜温层内。研究对分级粒径（0.2~3 μm及>3.0 μm）的叶绿素a（chlorophyll a, Chla）动态变化进行了为期42天的连续监测，监测时段始于实验扰动事件发生后。混合作用破坏了水体热分层结构，提升了湖上层中溶解态营养盐与二氧化碳的浓度，并改变了其光照条件。由此，混合可在发生后一周内提升0.2~3.0 μm粒径级别的Chla浓度；2~3周后，混合还会导致大粒径级别的Chla浓度升高，这一现象与束丝藻属（Dolichospermum）物种水华的发生密切相关。