TemBi 2014 mesocosm study: Summer storm impact on primary production rates and enzyme activities 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. 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.本研究在施特林湖（Lake Stechlin，https://www.lake-lab.de）的大型实验围隔（容积约1200 m³，水深约16 m）中，通过将斜温层（metalimnion）与湖下层（hypolimnion）的深层水体混合至上层混合层（epilimnion，湖上层）的方式，模拟了一场实验性夏季风暴。本次混合过程对深层叶绿素最大值层（deep chlorophyll maximum, DCM）造成了扰动；该层在实验开展期间本就存在于施特林湖，且在围隔充注阶段位于各围隔的斜温层中。实验扰动发生后的42天内，研究人员分别采用H¹⁴CO₃⁻标记分级粒径样品的培养法，以及甲基伞形酮（MUF）底物类似物分析法，对初级生产力速率与胞外酶活性（exoenzyme activities，包括碱性磷酸酶alkaline phosphatase、β-葡萄糖苷酶beta-glucosidase、亮氨酸氨肽酶leucine aminopeptidase）进行了监测。水体混合破坏了热分层（thermal stratification）结构，提升了溶解态营养盐与二氧化碳的浓度，并改变了湖上层的光照条件。因此，混合过程促进了浮游植物（phytoplankton）的生长，使得混合发生后一周内的初级生产力速率显著提升。