Scholarly record

MULTIANNUAL CHANGES IN SEDIMENT PHOSPHORUS OF WIELKOPOLSKIE LAKE (WIELKOPOLSKIE LAKE DISTRICT, WESTERN POLAND)

Renata Augustyniak

Abstract

The object of study was Wolszty?skie Lake, (area 124.2 ha, max depth 4.2 m). That water body is flow-through lake type and it is alimented by Dojca River and total catchment area is 193,5 km2. The lake was restored using phosphorus inactivation method ? in the 2005-2006 years an aluminum coagulant PAX 18 was used for treatment and in 2013-2014 years ? iron coagulant PIX 111. The results of research revealed, that the amounts of phosphorus fractions in the bottom sediment have changed. In the 20 cm thick sediment cores taken in 2016 year the clearly higher NaOH-rP (P bound with Al) fraction amounts in the deepest section of core (15-20 cm)were noted (ca. 0.280 mg P g-1 dw), comparing to the upper sediment layer (ca. 0.125 mg P g-1 dw). It is worth noting that the sediment deposition in the lake is very quick ? during the 10 years after restoration using aluminum coagulant the layer ca. 15 cm of fresh sediment was deposited ? taking into account the sediment compression phenomenon the sedimentation rate can be assessed as 1.5-2 cm per year, which is very high value for even eutrophic lakes. Probably the second lake treatment influenced on the sediment deposition rate as well. The obtain research results allow to suppose that the time range of positive restoration effect durability in the lakes with such high sedimentation rate will be limited.

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