Spectral analysis of water level fluctuations in Belarusian and Polish lakes

Data regarding 25 lakes (9 Belarusian and 16 Polish) provided the basis for spectral analysis of water level fluctuations. The obtained output data concerned a 55-year observation sequence covering the years 1956-2010. The selection of lakes was determined by two factors, i.e. data continuity and inconsiderable anthropogenic impact. The lakes were divided into three groups depending on the course of the water level spectrum. The first group included the highest number of lakes (14) which were distinguished by smooth curves with no significant peaks (e.g. Lake Wygonoszczańskie). The second group shows a four-year variability (e.g. Lake Łukomskie). The third group is distinguished by an even peak of three-year water fluctuation (e.g. Lake Łebsko). The location of the lakes categorised into those three groups suggests a certain regionalisation. The first group is represented by lakes of central and northern Belarus, and eastern Poland. The second group includes lakes of eastern Belarus, and the third group - lakes of central and northern Poland. This suggests that alongside local factors, the location of the distinguished groups of lakes may also be determined by regional factors. Presumably, continentalism of climate increasing in an eastwards direction is one of the key factors responsible for the detected regional diversity of lake water level fluctuations.