80
A. Choi´ nski and R. Skowron
resources. Due to the combined effect of many natural and anthropogenic factors,
it is difficult to perform hierarchization of their effects on a given lake. Due to this,
attempts to solving the problem of the decline of lakes in the Wielkopolska-Kujawy
Lake District require the collaboration of specialists from different disciplines of
Earth sciences [26].
Changes in the surface area of lakes are undoubtedly largely determined by local
factors. An example of this type of determination are results of research by [27].
Changes in the surface area of three lakes located near each other (in the Oder River
catchment) were completely different. Over approximately 170 years, the surface
area of one lake was absolutely stable, that of the other drastically decreased, and
the third one was divided into three smaller basins – Fig. 5.6.
In order to determine how the course of time affects the longevity of lakes [28]
performed the following analysis. In zones located between the ranges of subsequent
phases of the last glaciation, i.e. the Leszno and Pozna´ n, Pozna´ n and Pomneranian,
and north of the Pomeranian phase, the number of lakes was determined along with
their total water resources, and total surface area. Knowing the surface area of the
designated areas, three indices were determined for each of them, i.e. lake density,
mean depth of lakes, and water resources in mm. The values were referred to the
surface area, obtaining the layer of lake waters. The analysis shows that the lakes
are increasingly “older” towards the south. Lake density consequently decreases
southwards, and mean depth of lakes and the layer of water resources decreases [28].
Apart from many described cases of a decrease in the surface area of lakes, also
cases of complete disappearance occur. The disappearance of Lake Jelenino near
Szczecinek can be described as spectacular [29]. At the end of the eighteenth century,
the lake had a surface area of 495.2 ha. As a result of intensive melioration, its basin
lost water entirely. If the lake existed nowadays, it would be one of the largest lakes
in Poland in terms of surface area.
A decrease in the total area of lakes in the Pomeranian Lake District throughout
40–50 years in the twentieth century by 9.69% suggests the process of their decline.
This also concerns the remaining regions (Lake Districts) where the decline is even
greater [1]. The decline of lakes is justly particularly associated with a decrease
in the water level, accumulation of sediment in the lake basin, and progressing
eutrophication.
Based on cartographic materials for 256 lakes in the Wielkopolska Lake District,
[30] analysed changes in the degree of overgrowing of lakes throughout the last
60 years. As a result, a decrease in the surface area of lakes by 0.6% was determined (from 28 152.6 to 27 983.7 ha). Simultaneously, the surface area occupied by
emergent vegetation increased by 1.7%. The tendency is confirmed by overgrowing
presented for two selected lakes in the region with polymictic character [31].
Based on cartographic materials and aerial photographs, [14] analysed changes
in the degree of overgrowing of lakes for 893 lakes located in lake districts in Poland
(Pomeranian, Masurian, and Wielkopolska Lake District). The lakes were selected
based on the existing bathymetric plans and information on their overgrowing and
depth relations. Over the last 60 years, a decrease in the surface area of lakes by 1.9%
was observed (from 140 975.0 to 138 273.7 ha). The surface area of lakes occupied
A. Choi´ nski and R. Skowron
resources. Due to the combined effect of many natural and anthropogenic factors,
it is difficult to perform hierarchization of their effects on a given lake. Due to this,
attempts to solving the problem of the decline of lakes in the Wielkopolska-Kujawy
Lake District require the collaboration of specialists from different disciplines of
Earth sciences [26].
Changes in the surface area of lakes are undoubtedly largely determined by local
factors. An example of this type of determination are results of research by [27].
Changes in the surface area of three lakes located near each other (in the Oder River
catchment) were completely different. Over approximately 170 years, the surface
area of one lake was absolutely stable, that of the other drastically decreased, and
the third one was divided into three smaller basins – Fig. 5.6.
In order to determine how the course of time affects the longevity of lakes [28]
performed the following analysis. In zones located between the ranges of subsequent
phases of the last glaciation, i.e. the Leszno and Pozna´ n, Pozna´ n and Pomneranian,
and north of the Pomeranian phase, the number of lakes was determined along with
their total water resources, and total surface area. Knowing the surface area of the
designated areas, three indices were determined for each of them, i.e. lake density,
mean depth of lakes, and water resources in mm. The values were referred to the
surface area, obtaining the layer of lake waters. The analysis shows that the lakes
are increasingly “older” towards the south. Lake density consequently decreases
southwards, and mean depth of lakes and the layer of water resources decreases [28].
Apart from many described cases of a decrease in the surface area of lakes, also
cases of complete disappearance occur. The disappearance of Lake Jelenino near
Szczecinek can be described as spectacular [29]. At the end of the eighteenth century,
the lake had a surface area of 495.2 ha. As a result of intensive melioration, its basin
lost water entirely. If the lake existed nowadays, it would be one of the largest lakes
in Poland in terms of surface area.
A decrease in the total area of lakes in the Pomeranian Lake District throughout
40–50 years in the twentieth century by 9.69% suggests the process of their decline.
This also concerns the remaining regions (Lake Districts) where the decline is even
greater [1]. The decline of lakes is justly particularly associated with a decrease
in the water level, accumulation of sediment in the lake basin, and progressing
eutrophication.
Based on cartographic materials for 256 lakes in the Wielkopolska Lake District,
[30] analysed changes in the degree of overgrowing of lakes throughout the last
60 years. As a result, a decrease in the surface area of lakes by 0.6% was determined (from 28 152.6 to 27 983.7 ha). Simultaneously, the surface area occupied by
emergent vegetation increased by 1.7%. The tendency is confirmed by overgrowing
presented for two selected lakes in the region with polymictic character [31].
Based on cartographic materials and aerial photographs, [14] analysed changes
in the degree of overgrowing of lakes for 893 lakes located in lake districts in Poland
(Pomeranian, Masurian, and Wielkopolska Lake District). The lakes were selected
based on the existing bathymetric plans and information on their overgrowing and
depth relations. Over the last 60 years, a decrease in the surface area of lakes by 1.9%
was observed (from 140 975.0 to 138 273.7 ha). The surface area of lakes occupied