Diurnal variation in the convection-driven vertical distribution of phytoplankton under ice and after ice-off in large Lake Onego (Russia)

Abstract

When sunlight penetrates the ice layer covering lakes in winter, it warms the top water layer and sets up convection, with several potentially contrasting effects on phytoplankton. While convective mixing keeps cells in suspension and prevents sedimentation losses, it may also transport phytoplankton well below the euphotic zone. We investigated diurnal variations in the vertical distribution of phytoplankton under ice and just after ice-off in Lake Onego (Russia), a lake with moderate to high colored dissolved organic carbon (CDOM) levels. We showed that diurnal variation in convection under ice restricts phytoplankton access to light in the morning hours to a narrow euphotic zone, whereas cells are mixed through a deep aphotic layer in the afternoon. After ice-off, low chlorophyll a was found on the open-water side of the thermal bar as convection distributed cells throughout the water column. By contrast, the inshore side had significantly higher concentrations of chlorophyll a (p < 0.001) because the mixing depth brought about by diurnal microstratification was reduced, resulting in greater access to light in the afternoon. Overnight, convective cooling broke down microstratification, which redeveloped the next day. Our work highlights the importance of studying diurnal variation in light availability for photoautotrophic growth, both under ice and after ice-off in lakes characterized by high CDOM.

Fasting or feeding: A planktonic food web under lake ice

“…This study was conducted between the 15 and 17 March 2017 in Petrozavodsk Bay (depth of 27 m) in the western part of the lake (61°48′26.8″N, 34°26′01.1″E). The waters are yellow‐stained, oligo‐mesotrophic with concentrations of dissolved organic carbon ranging from 9 to 27 mg C/L under the ice (Suarez et al., 2019). At the sampling dates, the lake was inversely stratified, with water temperatures ranging between 0 and 1°C (Figure 1).…”

“…Under‐ice convection developed during daytime down to the 10–15 m depth and was maintained until sunset (19:00) and finally slowed down and stopped around 21:00 (Bouffard et al., 2019). Daily convection entrained the phytoplankton below the photic depth, down to the 10–15m depths (Suarez et al., 2019). The chlorophyll a concentration was low: 0.3 ± 0.2 μg/L (mean ± SD ) in the convective layer (Figure 1, Suarez et al., 2019).…”

“…Daily convection entrained the phytoplankton below the photic depth, down to the 10–15m depths (Suarez et al., 2019). The chlorophyll a concentration was low: 0.3 ± 0.2 μg/L (mean ± SD ) in the convective layer (Figure 1, Suarez et al., 2019). The diatom Aulacoseira sp .…”

“…dominated the assemblage (>90% of total phytoplankton biovolume) while the remaining 10% comprised other diatoms (5%), the dinophyte Peridium pusillum, the Chrysophyceae Mallomonas sp. and the Cryptophyceae Chroomonas sp., Cryptomonas sp., and Komma caudata (5%) (Suarez et al., 2019).…”

Circadian Variability of Dissolved Oxygen Content as an Indicator of the Metabolism of an Ice Covered Lake Ecosystem

“…Подобный характер вертикального распределения фитопланктона был обнаружен в финском озере Enonselka в период весеннего подледного перемешивания [Salmi, Salonen, 2016] и отражал влияние конвективных токов на перемещение клеток водорослей по водному столбу. согласно принятой в настоящее время гипотезе, конвективные движения способствуют развитию планктонного сообщества в покрытых льдом водоемах Jewson et al, 2009;Salmi, Salonen, 2016;Suarez et al, 2019], обеспечивая перенос биогенных веществ и удерживая клетки водорослей в пределах фотической зоны. отмечается также, что нисходящие конвективные токи могут выносить клетки водорослей ниже фотической зоны, что понижает скорость фотосинтеза [Suarez et al, 2019].…”