Temperature and Oxygen Regime of the Shallow Ice-covered Lake in Winter and Spring

The present study demonstrates a wide inter-annual, seasonal, synoptic and small-scale variability of the ice, temperature and dissolved oxygen regime of small Lake Vendyurskoe (Karelia, Russia) during winter, including periods of formation and destruction of ice cover on the basis of long-term observations (1995-2011). The incident, reflected and penetrating through the ice solar radiation were measured. The use a highly sensitive equipment for measuring water temperature and dissolved oxygen with a small time step (from 10 seconds to one minute), allowed us to obtain fundamentally new information on the time evolution of heat and mass transfer in the bottom boundary layer during winter. Data analysis indicates the presence of fluctuations in water temperature and dissolved oxygen in a wide range of time scales at different levels of the water column of shallow lakes throughout the winter. The main features of the temperature dynamics in the upper convective layer during the spring convection are described. The vertical velocities as a function of the kinematic heat flux at the lower boundary of the ice are estimated. Chlorophyll "a" for four groups of phytoplankton (green, blue-green, diatoms and cryptophytes) was measured during spring 2011. Based on measurements of solar radiation fluxes at the upper and lower boundaries of ice, water temperature, and chlorophyll "a", it is shown that the vertical convection currents keeps phytoplankton mostly within the convective mixed layer.