Autotrophic and heterotrophic plankton under ice in a eutrophic temperate lake

Abstract

Ice cover can considerably influence the food web structure and dynamics of lake ecosystems during winter. The aim of this study was to test the hypothesis that, due to unfavourable conditions, abundances of planktonic organisms are low under ice. The components of the microbial loop (nanoflagellates, ciliates) and the classical food web (algae, rotifers, crustaceans) were investigated in a eutrophic lake from January to April, at 7-day intervals. The phytoplankton was dominated by the mixotrophic chrysophyte Synura uvella, which formed an intense phytoplankton bloom. Nanoflagellates (mostly heterotrophic forms) and ciliates (oligotrichs, prostomatids) were present in relatively high numbers. Rotifers were represented by the algivorous taxa (Notholca squamula, Polyarthra dolichoptera) and reached surprisingly high abundances. There were no significant correlations between physical parameters and protists, but correlations were apparent between the thickness of the ice and the numbers of cyanobacteria, diatoms (negative) and chrysophytes (positive). The absence of crustaceans and relationships between rotifers and both algae and nanoflagellates indicate that these groups were probably a crucial factor determining the abundance and composition of the rotifer community. These results suggest that the microbial loop had a central role in the functioning of the ecosystem under ice in this eutrophic lake.

Dissolved oxygen dynamics under ice: Three winters of high‐frequency data from Lake Tovel, Italy

“…We suggest that in 2016 seasonal DO consumption at 5 m was compensated by photosynthetic activity and/or physical processes leading to the observed DO increase. Algal photosynthetic activity compensates for respiration, but under‐ice conditions are considered harsh, and phytoplankton abundances tend to be low with respect to ice‐free periods [ Hampton et al ., ], even though algae adapted to low light conditions and cold temperature can thrive [ Bertilsson et al ., ; Twiss et al ., ; Kalinowska and Grabowska , ]. In Lake Tovel, algal biomass is low [ Cellamare et al ., ], and most of the phytoplankton community is composed of mixotrophs (chrysophytes, cryptomonads, and dinoflagellates) and osmotrophs (diatoms) that are adapted to low light and cold temperatures [ Flaim et al ., ; Cellamare et al ., ].…”

“…Winter DO concentrations have long‐lasting impacts on the subsequent season, and this legacy effect has led to a renewed interest in understanding the ecological processes occurring under ice [ Hampton et al ., ]. Despite half of the world's lakes periodically freezing [ Hampton et al ., ], understanding DO dynamics under ice is hampered by the scarcity of limnological studies in winter [ Salonen et al ., ; Hampton et al ., ; Kalinowska and Grabowska , ], when snow and ice often restrict site accessibility, sampling, and measurements. Therefore, the relatively few studies of gas evolution (drivers of CO 2 variability or DO depletion rates) under ice often rely on occasional probe profiles or measurements based on headspace analysis or calculations [e.g., Welch and Bergmann , ; Catalan , ; Terzhevik et al ., ; Karlsson et al ., ; Denfeld et al ., ].…”

Comparison of ice‐on and ice‐off abiotic and biotic parameters in three eutrophic lakes

“…The winter biomass of phytoplankton may exceed values noted during the summer blooms of cyanobacteria (Kalinowska & Grabowska, ). Among phytoplankton, only mixotrophic chrysophytes can be more abundant in winter under the ice than in the summer and comparable to the spring and autumn values (Butts & Carrick, ; Kalinowska & Grabowska, ).…”

“…It has been shown that nitrate‐nitrogen concentrations may be higher in winter than in summer (Agbeti & Smol, ). The numbers and biomass of protozooplankton and the abundances of crustacean zooplankton are usually low during winter compared to other seasons (Agbeti & Smol, ; Kalinowska & Grabowska, ), while both maximal and mean rotifer numbers may be higher under ice than during the autumn and comparable to the summer values (Kalinowska & Grabowska, ). The winter biomass of phytoplankton may exceed values noted during the summer blooms of cyanobacteria (Kalinowska & Grabowska, ).…”

“…The numbers and biomass of protozooplankton and the abundances of crustacean zooplankton are usually low during winter compared to other seasons (Agbeti & Smol, ; Kalinowska & Grabowska, ), while both maximal and mean rotifer numbers may be higher under ice than during the autumn and comparable to the summer values (Kalinowska & Grabowska, ). The winter biomass of phytoplankton may exceed values noted during the summer blooms of cyanobacteria (Kalinowska & Grabowska, ). Among phytoplankton, only mixotrophic chrysophytes can be more abundant in winter under the ice than in the summer and comparable to the spring and autumn values (Butts & Carrick, ; Kalinowska & Grabowska, ).…”