Lake evolution in the Żnin region in the years 1912–1960 (central Poland)
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Date
2013
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Wydział Nauk Geograficznych i Geologicznych Uniwersytetu im. Adama Mickiewicza
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Abstract
The evolution of lakes, which, in the final stage, leads to their disappearance, is mainly based on the
analysis of surface area change. However, there is one more, frequently overlooked process, which determines
lake disappearance – namely the lake shallowing. The present paper presents the direction and rate of such
evolution, taking both these processes into account. It is a comparative analysis of 9 lakes in the Żnin region –
which has the greatest water deficit in the whole of Poland. Based on bathymetric plans from two periods (early
20th century and early 60’s of the 20th century), the author was able not only to evaluate the scale of surface area
change but also to determine the value of lake basins volume change. Both these values were negative and
amounted 9.1% and 14.9% respectively. Assuming that the said processes are invariable, the prospective period
of lake functioning is about 500 years when taking into consideration surface area change only, and is 150 years
shorter when allowing for aquatic resources change. The presented approach to lake disappearance analysis,
which treats this phenomenon as a decline in aquatic resources rather than a simple decrease in surface area, is
more reliable and therefore, scientific works in this field should take the results of lake shallowing into consideration.
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Keywords
lake evolution, surface area change, shallowing, bathymetry
Citation
Quaestiones Geographicae vol. 32 (1), 2013, pp. 21-26.