The thermal structure of a shallow lake in early winter

The thermal structure of a shallow lake in the first month of its freeze up is shown to vary widely from year to year. The rate of temperature increase at different horizons of the water mass in early winter is evaluated, and warming of shallow and deep-water areas in the lake are shown to be uneven. The distribution of near-bed temperature as a function of water depth in the first weeks of freeze up features wide variations, though this relationship becomes more regular over time. Estimates of the effective thermal diffusivity are given for different seasons. The main periods in the variations in the heat content of water column in early winter are estimated.     

Hydrophysical aspects of oxygen regime formation in a shallow ice-covered lake

Long-term observational data on a small, shallow Lake Vendyurskoe (Karelia) were used to analyze the space and time dissolved-oxygen dynamics in winter. Biochemical consumption was found to play a leading role in the reduction of dissolved-oxygen concentration in lake water in winter. The total decrease in the amount of dissolved oxygen since the beginning of under-ice period until mid-April was shown to amount to one third of the initial value. The year-to-year variations in winter oxygen consumption are ~10%, suggesting the process to be stable in the years of observations. The rate of oxygen consumption and variations in dissolved oxygen content of lake water in winter were evaluated. The analysis and literary data allow us to conclude that the hydrophysical processes taking place in shallow lakes in winter have a considerable effect on their oxygen regime.     

Short Internal Waves in a Small Ice-Covered Lake

The high-precision observational data on water temperature obtained during seven winters in a small boreal lake are considered. The spectral analysis revealed that the oscillations with a period of about 27 min prevailed in a water column. This period is close to the theoretical estimate of the first mode of the longitudinal barotropic seiche. The variability of temperature oscillations, vertical velocity, and displacement of isotherms suggest the presence of short internal waves along with seiches. The amplitude of the internal waves is an order of magnitude greater than that of seiches, and the length of internal waves is two orders of magnitude less than the linear extent of the lake.     

Modeling climatic circulation of Onega Lake

The results of numerical modeling of Onega Lake climatic circulation are presented. The model used in this study was developed earlier and successfully applied to the reproduction of large-scale hydrodynamical processes in Ladoga Lake. The obtained results are of importance for the development of both models of nonreactive pollutant transport and ecosystem models of the water body. The developed model can be used to calculate currents and temperature fields for individual scenarios of external impacts on the water body, and the results of calculation of the climatic circulation can serve as initial approximations for scenario-based calculations.     

Nonlinear internal waves in a large lake

Comprehensive experiments on the large stratified Lake Onega have been implemented for the first time. Generation and destruction of nonlinear internal waves under different meteorological conditions have been studied.     

Absorption of Solar Radiation by Snow-and-Ice Cover of Lakes

Based on the analysis of data of many-year actinometric observations, a considerable temporal (interannual, seasonal, synoptic, and diurnal) and spatial variability of the albedo of the snow-and-ice cover of a shallow lake is shown. The ranges of variations in the albedo of snow and ice for a wide spectrum of the state of surface and weather conditions are presented. The variability of the thickness and structure of snow-and-ice cover is analyzed for different periods in winter. The results of field experiments aimed to determine the degree of absorption of solar radiation by snow and ice are presented. The effective coefficients of absorption of solar radiation by snow and ice are determined. The comparison of the observed and calculated values of the under-ice radiation has shown that the determined coefficients adequately describe the absorption of solar radiation by snow-and-ice cover.     

Effect of Under-Ice Light Intensity and Convective Mixing on Chlorophyll a Distribution in a Small Mesotrophic Lake

Water Resources - Data of long-term measurements of under-ice solar radiation, water temperature, and chlorophyll a are analyzed in four phytoplankton groups (green, diatoms, blue-green, and...     

Motion of water in an ice-covered shallow lake

The results of analysis of data collected by direct measurements of currents in shallow Vendyurskoe Lake in winter are given. The horizontal motions of water in the lake are shown to exist throughout the freeze up period. Dominating frequencies are identified in variations in water motion with periods close to those of the longitudinal and transverse seiches of the lake. Experiments are used to show that oscillatory motions of ice can serve a source of energy for the development of water mass movement in ice-covered lakes. Wind is shown to be the most likely factor generating oscillatory motions of water in ice-covered lakes. It is shown that the velocities of residual currents existing in a lake decrease in winter and their maximum values occur above the deepwater part of the lake within the first and second months of freeze-up.