A field study was carried out in three small shallow ice-covered lakes to study heat and mass fluxes and their spatial and temporal variability. During the main part of the winter, the heat flux at the ice-water interface, being of the order 0.5-1 W m−2, was dominated by conduction from water to ice and did not show any significant variations in time or space. The heat flux from sediments to water was the main source for the lake water heating during early and mid-winter, being depth-dependent and 1-4.5 W m−2 in early winter, and 0.5-3 W m−2 in late winter. A heat transport from shallow regions to deep parts was shown to occur during the winter, being of the same order as the vertical fluxes, and should thus be accounted for in any attempt to predict the temperature evolution in an ice covered lake.
The salt flux from sediments was found to be of the order 1-10 × 10−10 kg m−2 s-l. A comparison of this flux with salt content changes indicates that the former is of the same order as the horizontal salt flux which is directed from shallow regions to the deeper parts of a lake during winter.