The Ice Regime of Lake Raduńskie Górne (Kashubian Lakeland, Northern Poland)

The paper presents assessment results of the ice dynamics on Lake Raduńskie Górne (Upper Radunia Lake) based on long-term observations of the course of ice phenomena. Interannual changes in lake ice phenology parameters (freeze-onset, ice-on, freeze duration, melt-onset, permanent ice cover duration, ice-off, melt duration) in the years 1961–2010 are discussed. In addition, the ice cover thickness was taken into consideration. The analysed parameters of ice phenology were compared to each other as well as to the mean air and water temperatures of the winter half-year (November–April). The main periods of the ice regime of the lake have been determined and described. The permanent ice cover constitutes on average 79%, freeze-up period 13%, and break-up period 8% of the whole time of ice phenomena. It was shown that the weather parameters crucial for ice formation are the mean air and surface water temperatures. On Lake Raduńskie Górne the ice phenomena can only occur when mean air temperature in the winter half-year, at Borucino wheather station, is lower than 4.9 °C, and water temperature (at a depth of 0.4 m) is lower than 5.7 °C. In turn permanent ice cover is created when the mean air temperature of the winter half-year is lower than 3.9 °C. The maximum and mean ice cover thickness on Lake Raduńskie Górne ranged, respectively, from 0.5 to 50 cm, and from 0.5 to 38.3 cm. These parameters were strongly positively correlated (r = 0.87–0.88, p < 0.05) with the duration of the ice cover period.