DIATOMS IN THE THANATOCOENOSIS OF THE LAKE ZAPOVEDNOYE (EVENKIYA)

23-2

CIRCULATION REGIME AND REDOX-CONDITIONS IN SALINE LAKE SHIRA (KHAKASIA, SIBERIA): FROM MODERN OBSERVATIONS TO PALEO-RECONSTRUCTION

93-9

Global data set of long-term summertime vertical temperature profiles in 153 lakes

peer reviewedClimate change and other anthropogenic stressors have led to long-term changes in the thermal structure, including surface temperatures, deepwater temperatures, and vertical thermal gradients, in many lakes around the world. Though many studies highlight warming of surface water temperatures in lakes worldwide, less is known about long-term trends in full vertical thermal structure and deepwater temperatures, which have been changing less consistently in both direction and magnitude. Here, we present a globally-expansive data set of summertime in-situ vertical temperature profiles from 153 lakes, with one time series beginning as early as 1894. We also compiled lake geographic, morphometric, and water quality variables that can influence vertical thermal structure through a variety of potential mechanisms in these lakes. These long-term time series of vertical temperature profiles and corresponding lake characteristics serve as valuable data to help understand changes and drivers of lake thermal structure in a time of rapid global and ecological change. © 2021, The Author(s)

DIATOMS IN THE THANATOCOENOSIS OF THE LAKE ZAPOVEDNOYE (EVENKIYA)

23-2

DIATOMS IN THE THANATOCOENOSIS OF THE LAKE ZAPOVEDNOYE (EVENKIYA)

23-2

CIRCULATION REGIME AND REDOX-CONDITIONS IN SALINE LAKE SHIRA (KHAKASIA, SIBERIA): FROM MODERN OBSERVATIONS TO PALEO-RECONSTRUCTION

93-9

CIRCULATION REGIME AND REDOX-CONDITIONS IN SALINE LAKE SHIRA (KHAKASIA, SIBERIA): FROM MODERN OBSERVATIONS TO PALEO-RECONSTRUCTION

93-9

Some generalizations based on stratification and vertical mixing in meromictic Lake Shira, Russia, in the period 2002–2009

In a brackish, temperate, 24-m-deep Lake Shira, the profiles of salinity, temperature, oxygen and sulfide concentrations were measured on a seasonal basis from 2002 to 2009. The lake was shown to be meromictic with autumnal overturn restricted to mixolimnion. The depth of mixolimnion and position of oxic–anoxic interface varied annually. The spring mixing processes contribute to the formation of mixolimnion in autumn. The exceptionally windy spring of 2007 caused the deepening of mixolimnion in the winter of 2008. The winter position of oxic–anoxic interface was affected by the position of lower boundary of mixolimnion in all winters. The salinity in the winter mixolimnion increased compared with the autumn because of freezing out of salts from the upper water layers meters during ice formation and their dissolution in water below. The profiles of salinity and temperature were simulated by the mathematical 1-D model of temperature and salinity conditions taking into account ice formation. The simulated profiles generally coincided with the measured ones. The coincidence implies that simplified one-dimensional model can be applied to roughly describe salinity and density profiles and mixing behavior of Lake Shira.

A one-dimensional model of vertical stratification of Lake Shira focussed on winter conditions and ice cover

In meromictic lakes such as Lake Shira, horizontal inhomogeneity is small in comparison with vertical gradients. To determine the vertical distribution of temperature, salinity, and density of water in a deep zone of a Lake Shira, or other saline lakes, a one-dimensional (in vertical direction) mathematical model is presented. A special feature of this model is that it takes into account the process of ice formation. The model of ice formation is based on the one-phase Stefan problem with the linear temperature distribution in the solid phase. A convective mixed layer is formed under an ice cover due to salt extraction in the ice formation process. To obtain analytical solutions for the vertical distribution of temperature, salinity, and density of water, we use a scheme of vertical structure in the form of several layers. In spring, the ice melts as top and bottom. These processes are taken into account in the model. The calculated profiles of salinity and temperature of Shira Lake are in good agreement with field measurement data for each season. Additionally, we focussed on the redox zone, which is the zone in which the aerobic layers of a water column meet the anaerobic ones. Hyperactivity of plankton communities is observed in this zone in lakes with hydrogen sulphide monimolimnion, and Lake Shira is among them. The location of the redox zone in the lake, which is estimated from field measurements, coincides with a sharp increase in density (the pycnocline) during autumn and winter. During spring and summer, the redox zone is deeper than the pycnocline. The location of pycnocline calculated with the hydro physical model is in good agreement with field measurement data.

Effect of winter conditions on distributions of anoxic phototrophic bacteria in two meromictic lakes in Siberia, Russia

The year-to-year variations of vertical distribution and biomass of anoxic phototrophic bacteria were studied during ice periods 2003–2005 and 2007–2008 in meromictic lakes Shira and Shunet (Southern Siberia, Russian Federation). The bacterial layers in chemocline of both lakes were sampled with a thin-layer hydraulic multi-syringe sampler. In winter, biomass of purple sulphur bacteria varied considerably depending on the amount of light penetrating into the chemocline through the ice and snow cover. In relatively weakly stratified, brackish Shira Lake, the depth of chemocline varied between winters, so that light intensity for purple sulphur bacteria inhabiting this zone differed. In Shira Lake, increased transparency of mixolimnion in winter, high chemocline position and absence of snow resulted in light intensity and biomass of purple sulphur bacteria exceeding the summer values in the chemocline of the lake. We could monitor snow cover at the lake surface using remote sensing and therefore estimate dynamics and amount of light under ice and its availability for phototrophic organisms. In Shunet Lake, the light intensities in the chemocline and biomasses of purple sulphur bacteria were always lower in winter than in summer, but the biomasses of green sulphur bacteria were similar.