78
A. Choi´ nski and R. Skowron
of the climate, they are also largely determined by a group of individual features of
lake catchments.
Very considerable changes occurred within the range of Lake Gopło as a result of
regulatory measures and melioration works performed in the Note´ c River valley in
the years 1775–1878. The measures caused a decrease in the water level in the lake
by 3.2–3.3 m, from 80.20 m amsl to below 77.00 m amsl [17]. A consequence of
the changes is the division of former Lake Gopło into the modern lake and several
smaller ones (Szarlej, Tryszczyn, Łunin, Gocanowskie, and Mielno) (Fig. 5.5). For
Lake Gopło, changes in the volume of the lake in the analysed period of 246 years
decreased from 235.8 to 76.7 million m
3 . Therefore, the present lake only fills the
deepest parts of the former Lake Gopło, constituting only 23.4% of its original surface
area, and only 32.5% of its volume.
In the Pomeranian Lake District, the effect of all processes occurring in lakes is an
evident succession of vegetation in lakes [23]. A good indicator showing an increase
in vegetation succession is the index of overgrowing of the shoreline (ha · km
−1 ). The
value of the index from the turn of the 1950s and 1960s (preparation of bathymetric
plans) is 0.98 ha · km
−1 , and that from the turn of the first and second decade of the
twenty-first century (60 years of difference) already reaches 1.14 ha · km
−1 . This
is strong evidence of an increase in overgrowing of lakes and vegetation succession
irrespective of the type of vegetation [24].
The performed calculations with the application of a digital terrain model showed
that the surface area of Lake Gopło in the period from the second half of the eighteenth
century to the end of the first decade of the nineteenth century (1772–2010) decreased
from 9 245.2 to 2 163.9 ha, i.e. by 76.6%.
Lake Ostrowskie (Gnie´ znie´ nskie Lake District) also decreased its surface area
but to a considerably lower degree. In the years 1887–2010, the total decrease in the
surface area was 74.9 ha, i.e. 23.5%. Simultaneously with a decrease in the surface
area of the analysed lakes, their water resources were also reduced. Lake Gopło
decreased its volume by more than 67%, and Lake Ostrowskie by 21% [18].
Based on cartographic and teledetection materials, and geodesic measurements,
changes in the morphometry of Lake Ostrowskie were traced throughout the last
123 years. As a result of a decrease in the water level, caused by various factors, the
modern lake was divided into two separate basins (eastern and western). It caused a
decrease in its surface area by 242.0 ha, and volume by 28.9%, whereas over the last
28 years by as much as 18.3% [25].
The effect of extensive regulation works conducted in the area of Wielkopolska
and Kujawy generally involving drying of wetlands, straightening of river channels,
channelling many sections of rivers, and incorporation of closed-drainage lakes to
the outflow system was a decrease in the water level on many lakes by an average of
0.6–0.8 m, and in extreme cases even by 1.1–1.4 m. Such a considerable interference
caused a decrease in their surface area by a dozen, and in extreme cases even by 80%
[16].
The problem of the decline of lakes is exceptionally complex, particularly in the
Wielkopolska-Kujawy Lake District, located in an area exceptional at the scale of
the country due to low supply of atmospheric precipitation and therefore small water
A. Choi´ nski and R. Skowron
of the climate, they are also largely determined by a group of individual features of
lake catchments.
Very considerable changes occurred within the range of Lake Gopło as a result of
regulatory measures and melioration works performed in the Note´ c River valley in
the years 1775–1878. The measures caused a decrease in the water level in the lake
by 3.2–3.3 m, from 80.20 m amsl to below 77.00 m amsl [17]. A consequence of
the changes is the division of former Lake Gopło into the modern lake and several
smaller ones (Szarlej, Tryszczyn, Łunin, Gocanowskie, and Mielno) (Fig. 5.5). For
Lake Gopło, changes in the volume of the lake in the analysed period of 246 years
decreased from 235.8 to 76.7 million m
3 . Therefore, the present lake only fills the
deepest parts of the former Lake Gopło, constituting only 23.4% of its original surface
area, and only 32.5% of its volume.
In the Pomeranian Lake District, the effect of all processes occurring in lakes is an
evident succession of vegetation in lakes [23]. A good indicator showing an increase
in vegetation succession is the index of overgrowing of the shoreline (ha · km
−1 ). The
value of the index from the turn of the 1950s and 1960s (preparation of bathymetric
plans) is 0.98 ha · km
−1 , and that from the turn of the first and second decade of the
twenty-first century (60 years of difference) already reaches 1.14 ha · km
−1 . This
is strong evidence of an increase in overgrowing of lakes and vegetation succession
irrespective of the type of vegetation [24].
The performed calculations with the application of a digital terrain model showed
that the surface area of Lake Gopło in the period from the second half of the eighteenth
century to the end of the first decade of the nineteenth century (1772–2010) decreased
from 9 245.2 to 2 163.9 ha, i.e. by 76.6%.
Lake Ostrowskie (Gnie´ znie´ nskie Lake District) also decreased its surface area
but to a considerably lower degree. In the years 1887–2010, the total decrease in the
surface area was 74.9 ha, i.e. 23.5%. Simultaneously with a decrease in the surface
area of the analysed lakes, their water resources were also reduced. Lake Gopło
decreased its volume by more than 67%, and Lake Ostrowskie by 21% [18].
Based on cartographic and teledetection materials, and geodesic measurements,
changes in the morphometry of Lake Ostrowskie were traced throughout the last
123 years. As a result of a decrease in the water level, caused by various factors, the
modern lake was divided into two separate basins (eastern and western). It caused a
decrease in its surface area by 242.0 ha, and volume by 28.9%, whereas over the last
28 years by as much as 18.3% [25].
The effect of extensive regulation works conducted in the area of Wielkopolska
and Kujawy generally involving drying of wetlands, straightening of river channels,
channelling many sections of rivers, and incorporation of closed-drainage lakes to
the outflow system was a decrease in the water level on many lakes by an average of
0.6–0.8 m, and in extreme cases even by 1.1–1.4 m. Such a considerable interference
caused a decrease in their surface area by a dozen, and in extreme cases even by 80%
[16].
The problem of the decline of lakes is exceptionally complex, particularly in the
Wielkopolska-Kujawy Lake District, located in an area exceptional at the scale of
the country due to low supply of atmospheric precipitation and therefore small water