title: Planktonic events may cause polymictic-dimictic regime shifts in temperate lakes.
abstract: Water transparency affects the thermal structure of lakes, and within certain lake depth ranges, it can determine whether a lake mixes regularly (polymictic regime) or stratifies continuously (dimictic regime) from spring through summer. Phytoplankton biomass can influence transparency but the effect of its seasonal pattern on stratification is unknown. Therefore we analysed long term field data from two lakes of similar depth, transparency and climate but one polymictic and one dimictic, and simulated a conceptual lake with a hydrodynamic model. Transparency in the study lakes was typically low during spring and summer blooms and high in between during the clear water phase (CWP), caused when zooplankton graze the spring bloom. The effect of variability of transparency on thermal structure was stronger at intermediate transparency and stronger during a critical window in spring when the rate of lake warming is highest. Whereas the spring bloom strengthened stratification in spring, the CWP weakened it in summer. The presence or absence of the CWP influenced stratification duration and under some conditions determined the mixing regime. Therefore seasonal plankton dynamics, including biotic interactions that suppress the CWP, can influence lake temperatures, stratification duration, and potentially also the mixing regime.
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries Department of Ecohydrology, Müggelseedamm 310, 12587 Berlin, Germany.
authors.forename: Tom
authors.initials: T
authors.lastname: Shatwell
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries Department of Ecosystem Research, Müggelseedamm 301, 12587 Berlin, Germany.|Freie Universität Berlin Department of Biology, Chemistry, Pharmacy, Takustr. 3, 14195 Berlin, Germany.
authors.forename: Rita
authors.initials: R
authors.lastname: Adrian
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries Department of Ecohydrology, Müggelseedamm 310, 12587 Berlin, Germany.
authors.forename: Georgiy
authors.initials: G
authors.lastname: Kirillin
mesh_terms: D000818:Animals; D060106:Lakes / Q000382:microbiology*; D055585:Physical Phenomena; D010839:Phytoplankton / Q000254:growth & development*; D011157:Population Dynamics; D012621:Seasons; D013696:Temperature; D014867:Water; D015048:Zooplankton / Q000254:growth & development*
chemical_list: D014867:Water