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Precipitation of phosphorus
in the zone of river and lake water mixing: r. Hańcza and Lake Wigry
(North-East Poland) |
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Bogusław Zdanowski
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Department
of Hydrobiology, The Stanisław Sakowicz Inland Fisheries Institute, Oczapowskiego
10, 10-719 Olsztyn, Poland email: bzdanowski@infish.com.pl
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Abstract:
Studies on physico-chemical
parameters of water in Czarna Hańcza River and lakes
Hańcza and Wigry (North-East Poland) were carried out in 1991–1994 i.e. in
the period of maximal pollution of this river-lake system. Basic information
were obtained enabling explanation of high resistance of Lake Wigry to
eutrophication. It was shown that co-precipitation of phosphates on calcite
in the ecotone zone of Hańczańska Bay, where river waters mixed with lake
waters, was an important process. Sedimentation of these substances in this
lake part resulted in lower lake loading with phosphorus by as much as about
50%. The mechanisms were operating most of all during the vegetation season,
when water pH exceeded 8.3. Availability of phosphorus to phytoplankton
depended also on phosphate release from bottom sediments. The lowest rate of
this release was observed in Hańczańska Bay. On the other hand, in autumn and
winter the increase of organic matter decomposition and lowering of water pH
enabled free spreading of pollutants over the whole lake. |
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Key words: phosphorus, calcium, river-lake system,
ecotone, decalcification, precipitation, loading, eutrophication |