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

Abstract

Under‐ice dissolved oxygen (DO) metabolism and DO depletion are poorly understood, limiting our ability to predict how changing winter conditions will affect lake ecosystems. We analyzed under‐ice DO dynamics based on high‐frequency (HF) data at two depths (5 and 25 m) for three winters (January–March 2014, 2015, and 2016) in oligotrophic Lake Tovel (1178 m above sea level; maximum depth 39 m). Specifically, we assessed diel metabolic rates based on HF data of DO, temperature, and light for winter 2016 and seasonal DO depletion rates based on HF data of DO for all three winters. For 2016, calculations of metabolic rates were possible only for 34% and 3% of days at 5 and 25 m, respectively; these metabolic rates generally indicated net heterotrophy at both depths. Low success in modeling metabolic rates was attributed to low diel DO variability and anomalous diel DO patterns, probably linked to under‐ice physical processes. Seasonal DO patterns for the three winters showed increasing, decreasing, or stable DO trends at 5 m while at 25 m patterns always showed decreasing DO trends but with different rates. Our multiyear study permitted us to hypothesize that the observed intraannual and interannual differences in DO depletion can be attributed to variable snow cover determining the penetration of radiation and thus photosynthesis. This study brings new insights to DO dynamics in ice‐covered systems, highlights the challenges linked to under‐ice lake metabolism, and advocates for a modeling approach that includes physical processes.

Under‐ice metabolism in a shallow lake in a cold and arid climate

“…Thus, although irradiance decreased rapidly in the water column and PAR values at the bottom varied between 0 and 5 W/m 2 (unpublished data), even such a low level of PAR seemed to be high enough for photosynthesis to occur. Our observations are in accordance with Obertegger, Obrador, and Flaim () who analysed under‐ice DO dynamics in an oligotrophic lake, and with Hanke et al. () who studied phytoplankton growth and photosynthesis under thick snow and sea‐ice in Greenland.…”

A Small Temperate Lake in the 21st Century: Dynamics of Water Temperature, Ice Phenology, Dissolved Oxygen, and Chlorophyll a

“…In addition to water temperature, climate change also influences other important physical and biological state variables of temperate lakes, such as ice phenology, dissolved oxygen (DO), and chlorophyll a (Couture et al, ; Fang & Stefan, ; Kraemer et al, ). These variables regulate important biogeochemical processes (e.g., carbon burial and degradation) in both water and sediment columns (Evans et al, ; Ferland et al, ; Istvánovics & Honti, ; Müller et al, ; Obertegger et al, ) and are indicators of water quality (Dillon et al, ; Jiang et al, ). For instance, important cold‐water fish such as salmon and brown trout thrive in a habitat of combining high DO concentrations and low water temperature (Dillon et al, ; Jiang et al, ), typical for the hypolimnion of natural temperate oligotrophic lakes.…”

“…To date, our understanding of the future dynamics of these state variables in small temperate lakes is still limited (Couture et al, ; Fang & Stefan, ; Obertegger et al, ; Oliver et al, ; Yao et al, ). First, although the processes that control the dynamics of water temperature, ice phenology, DO, and chlorophyll a are closely interacted (Couture et al, ; Giling et al, ; Obertegger et al, ), the modeling studies for small temperate lakes usually only focused on one or two of these variables (Vincent et al, ; Yao et al, ) and few modeling studies have predicted the chlorophyll a dynamics (Fang & Stefan, ; Joehnk & Umlauf, ; Yao et al, ). Second, the difference of DO dynamics in surface and deep waters was less explored and the impacts of catchments on the future changes of lakes were sometimes ignored (Fang & Stefan, ).…”

High‐Frequency Observations of Temperature and Dissolved Oxygen Reveal Under‐Ice Convection in a Large Lake

“…The combined presence of ice cover and a stable stratification in winter has traditionally been assumed to inhibit vertical transport of oxygen from the atmosphere, and hence in shallow lakes, winter anoxic fish kills can occur (Golosov et al, 2007). More recent studies show that increased light levels in late winter lead to under-ice phytoplankton growth (Kim et al, 2015;Obertegger et al, 2017;Phillips & Fawley, 2002;Salmi & Salonen, 2016), which produces oxygen in the upper water column (Pernica et al, 2017). It is likely that the physical processes under the ice (Kirillin et al, 2012) are linked to the timing of the frequent presence of Geophysical Research Letters 10.1002/2017GL075373 large plankton concentrations observed in many lakes during winter (Hampton et al, 2017;Salmi & Salonen, 2016;Twiss et al, 2012).…”