In the paper it is shown that the lakes of the North-Eastern Poland fulfil various functions in the groundwater phase of the water circulation. The value of the resultant of the groundwater supply to the lake, and in some cases also its direction, depend on the volume of the water undergoing a total exchange in the reservoir in the given year. In through-flow lakes the runoff increase coefficient also influences this value.
Assessment of the ecological state of lakes as proposed by the Polish Limnological Society
The paper presents a method of assessment of the ecological state of lakes. It is based on methodology proposed by the Polish Limnological Society. According to this methodology, a set of indicators may be determined and may serve as a basis to make recommendations on what actions should be taken to maintain or restore a good ecological state of a lake. The set of indicators used for remedy recommendations includes: environmental pressure indicators that determine the rate of eutrophication in bodies of water, indicators of the state of the environment describing water quality and the balance of the water resources of a lake, and reaction indicators providing information on the degree of eutrophication of a lake.
The paper considers whether in recent years there have been changes in the structure of the water circulation in Lake Wigry, the main water body of the Wigry National Park. The volume and trends in the streams of water exchange in the lake have been assessed. They show that in recent years the horizontal water exchange is being reduced as the inflow to the lake is growing, mainly due to its main tributary, the Czarna Hańcza, while the outflow from the lake is decreasing. The paper examines whether these changes are reflected in the structure of the lake water circulation, which has been assessed on the basis of the lake water balance
Resuspension in lakes affects the quality of lake water. It is possible to model this process and visualize its outcomes using GIS tools. An assessment of the size of the zone of sediment resuspension was made for two lakes located in Northern Poland threatened by rapid eutrophication. For each of the lakes, four simulations using two methods for determining the effective wind length (F) (Model 1 and Model 2) and two methods for determining the wind wavelength (Lw) (Model A and Model B) were performed. The analysis, taking into account the morphometry of the studied lakes and anemometric conditions, indicated that the differentiator is the applied simulation method of calculating the wavelength caused by the wind. The analysis is theoretical in nature and the results need to be verified in the field..
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.