7 Water Quality in Main Dam Reservoirs in Poland
149
For example, the Solina reservoir on the upper San traps as much as 99% of load
transported by this river (average from the period of dam functioning), and other
deep reservoirs located in the Carpathians and Sudetes over 80% [32]. In shallow
reservoirs located in different parts of Poland (Czaniec, Goczałkowice, Włocławek,
Sulejów, D˛ ebe, Jeziorsko), the multiannual retention capacity of these reservoirs
ranges from 18% to about 50% [32]. Downstream of the barrage in Włocławek the
transport of suspended load in the Vistula is lower by 41%, and bed load by nearly
100% [20, 33]. Material accumulating in reservoirs has a huge impact on its ecological status because along with material trapped in the reservoir pollutants accumulate
in bottom sediments, including also toxic compounds and heavy metals [34]. The
suspended load is attributed to an important role in the transport of metals along
the course of the river [35]. Besides trapping the suspended load, the functioning of
dam reservoirs may favourably impact the reduction of selected pollutants in water
due to the process of self-purification, which is observed in retention reservoirs. In
the case of a big lowland reservoir, comparing quality parameters of water entering
the reservoir and exiting it, we may count on the reduction of heavy metal load by
70–90%, organic pollutants by about 50% and overall suspended load by 30%, what
was proven by [36] on the basis of studies of the Włocławek reservoir. Reactivation
of polluted sediments trapped in reservoirs, e.g. by waving, floods, dredging bottom
sediments or by shipping may lead to secondary water pollution. The capacity of the
reservoir to accumulate sediments also depends on hydrodynamic conditions.
An important factor influencing the concentration of mineral substances in reservoirs is their storing capacity and intensity of water exchange. As regards water
retention the following dam reservoirs have been included into the limnic group:
Solina, Czorsztyn, Jeziorsko, Goczałkowice, Dobczyce, Nysa, Turawa, Tresna,
Siemianówka, Mietków, Klimkówka, Rybnik, Kozłowa Góra, Bukówka, and Besko.
Average water retention time in the analysed reservoirs of the limnic type is
138.13 days. The longest retention period was recorded for Kozłowa Góra, where it
was as long as 307 days. Transitory reservoirs in the presented group are: Ro˙ znów,
Sulejów, Pilchowice, and Por˛ abka—average retention time in them is 32 days.
Reolimnic reservoirs include D˛ ebe, Włocławek, and Czaniec. Average retention time,
in this case, is 4.5 days. In the Włocławek reservoir, it is 5.6 days [36].
Usually water quality is potentially the best in reservoirs with the greatest depth
and volume of water mass and small total area of catchment, without point pollution
sources. However, different trends apply to water quality in shallow reservoirs with
scarce water resources, with vast catchment areas that are agriculturally used and
densely populated. An important factor that may influence the quality of surface
layers of water is the possibility of export of the so-called internal biogenic load,
which increases with growing trophism and is caused by the release of phosphates
from bottom sediments, particularly in anaerobic conditions. Additional phosphate
load in the summer period stimulates algae development leading to algal bloom [30].
149
For example, the Solina reservoir on the upper San traps as much as 99% of load
transported by this river (average from the period of dam functioning), and other
deep reservoirs located in the Carpathians and Sudetes over 80% [32]. In shallow
reservoirs located in different parts of Poland (Czaniec, Goczałkowice, Włocławek,
Sulejów, D˛ ebe, Jeziorsko), the multiannual retention capacity of these reservoirs
ranges from 18% to about 50% [32]. Downstream of the barrage in Włocławek the
transport of suspended load in the Vistula is lower by 41%, and bed load by nearly
100% [20, 33]. Material accumulating in reservoirs has a huge impact on its ecological status because along with material trapped in the reservoir pollutants accumulate
in bottom sediments, including also toxic compounds and heavy metals [34]. The
suspended load is attributed to an important role in the transport of metals along
the course of the river [35]. Besides trapping the suspended load, the functioning of
dam reservoirs may favourably impact the reduction of selected pollutants in water
due to the process of self-purification, which is observed in retention reservoirs. In
the case of a big lowland reservoir, comparing quality parameters of water entering
the reservoir and exiting it, we may count on the reduction of heavy metal load by
70–90%, organic pollutants by about 50% and overall suspended load by 30%, what
was proven by [36] on the basis of studies of the Włocławek reservoir. Reactivation
of polluted sediments trapped in reservoirs, e.g. by waving, floods, dredging bottom
sediments or by shipping may lead to secondary water pollution. The capacity of the
reservoir to accumulate sediments also depends on hydrodynamic conditions.
An important factor influencing the concentration of mineral substances in reservoirs is their storing capacity and intensity of water exchange. As regards water
retention the following dam reservoirs have been included into the limnic group:
Solina, Czorsztyn, Jeziorsko, Goczałkowice, Dobczyce, Nysa, Turawa, Tresna,
Siemianówka, Mietków, Klimkówka, Rybnik, Kozłowa Góra, Bukówka, and Besko.
Average water retention time in the analysed reservoirs of the limnic type is
138.13 days. The longest retention period was recorded for Kozłowa Góra, where it
was as long as 307 days. Transitory reservoirs in the presented group are: Ro˙ znów,
Sulejów, Pilchowice, and Por˛ abka—average retention time in them is 32 days.
Reolimnic reservoirs include D˛ ebe, Włocławek, and Czaniec. Average retention time,
in this case, is 4.5 days. In the Włocławek reservoir, it is 5.6 days [36].
Usually water quality is potentially the best in reservoirs with the greatest depth
and volume of water mass and small total area of catchment, without point pollution
sources. However, different trends apply to water quality in shallow reservoirs with
scarce water resources, with vast catchment areas that are agriculturally used and
densely populated. An important factor that may influence the quality of surface
layers of water is the possibility of export of the so-called internal biogenic load,
which increases with growing trophism and is caused by the release of phosphates
from bottom sediments, particularly in anaerobic conditions. Additional phosphate
load in the summer period stimulates algae development leading to algal bloom [30].