15 Monitoring of Small Catchments in …
361
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
1-11 1-12 1-01 1-02 1-03 1-04 1-05 1-06 1-07 1-08 1-09 1-10
Discharge (m 3
s -1
)
2015
2011
1994-2017
Fig. 15.11 The course of mean diurnal flow values in the Struga Toru´ nska at Koniczynka for a wet
year (2011) and a dry year (2015), and the mean flow in the years 1994–2017
surface water quality has caused the lake to overgrow, become excessively eutrophicated and subject to intense and prolonged phytoplankton bloom and hypoxias in
the summer.
The water flowing from the lake has a significant influence on the quality of water
in the Struga Toru´ nska at the upper part of the representative catchment and has much
lower concentrations of biogenic substances and increased organic matter content.
This was confirmed by analyses of the water at the Lipowiec site in 1993–
2017. Aerobic conditions in the summer were unfavourable, and the organic content
expressed using the five-day biochemical oxygen demand (BOD5) was increased.
The highest BOD5 occurred in the first years of observations when it often exceeded
8 mg O 2
. dm
−3 . On the other hand, the content of biogenic elements was reduced as
they were assimilated in the lake water (Table 15.3). The influence of the lake also
contributed to a reduced concentration of dissolved substances.
The measuring site at Koniczynka is located 10 km downstream of the Lipowiec
site. Along that stretch, the Struga Toru´ nska is subject to considerable anthropopressure, both from agricultural activities and from the effects of the nearby city of Toru´ n
Wojtczak. The results of observations indicated increased concentrations of biogenic
and mineral substances and suspended matter. Aerobic conditions in the water and
the organic matter content were more favourable.
Tests for the presence of heavy metals—aluminium, cadmium, copper, lead,
manganese, zinc, nickel, arsenic, iron and chromium—were carried out starting in
2007 at Lipowiec and Koniczynka. The heavy metal content was generally maintained below the detection limit or in quantities that did not pose a threat to the
aquatic environment.
Analysing changes in the concentrations of elementary parameters of the water
in the experimental catchment area of the Struga Toru´ nska in 1993–2017, it was
found that aerobic conditions improved along the course of the river. On average,
at Lipowiec, it was 7.5 mg O 2
. dm
−3 , and at Koniczynka 8.6 mg O 2
. dm
−3 . In the
361
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
1-11 1-12 1-01 1-02 1-03 1-04 1-05 1-06 1-07 1-08 1-09 1-10
Discharge (m 3
s -1
)
2015
2011
1994-2017
Fig. 15.11 The course of mean diurnal flow values in the Struga Toru´ nska at Koniczynka for a wet
year (2011) and a dry year (2015), and the mean flow in the years 1994–2017
surface water quality has caused the lake to overgrow, become excessively eutrophicated and subject to intense and prolonged phytoplankton bloom and hypoxias in
the summer.
The water flowing from the lake has a significant influence on the quality of water
in the Struga Toru´ nska at the upper part of the representative catchment and has much
lower concentrations of biogenic substances and increased organic matter content.
This was confirmed by analyses of the water at the Lipowiec site in 1993–
2017. Aerobic conditions in the summer were unfavourable, and the organic content
expressed using the five-day biochemical oxygen demand (BOD5) was increased.
The highest BOD5 occurred in the first years of observations when it often exceeded
8 mg O 2
. dm
−3 . On the other hand, the content of biogenic elements was reduced as
they were assimilated in the lake water (Table 15.3). The influence of the lake also
contributed to a reduced concentration of dissolved substances.
The measuring site at Koniczynka is located 10 km downstream of the Lipowiec
site. Along that stretch, the Struga Toru´ nska is subject to considerable anthropopressure, both from agricultural activities and from the effects of the nearby city of Toru´ n
Wojtczak. The results of observations indicated increased concentrations of biogenic
and mineral substances and suspended matter. Aerobic conditions in the water and
the organic matter content were more favourable.
Tests for the presence of heavy metals—aluminium, cadmium, copper, lead,
manganese, zinc, nickel, arsenic, iron and chromium—were carried out starting in
2007 at Lipowiec and Koniczynka. The heavy metal content was generally maintained below the detection limit or in quantities that did not pose a threat to the
aquatic environment.
Analysing changes in the concentrations of elementary parameters of the water
in the experimental catchment area of the Struga Toru´ nska in 1993–2017, it was
found that aerobic conditions improved along the course of the river. On average,
at Lipowiec, it was 7.5 mg O 2
. dm
−3 , and at Koniczynka 8.6 mg O 2
. dm
−3 . In the