Many lakes worldwide, especially shallow, experience great changes due to eutrophication, manifested in severe, usually toxic water blooms, disqualifying them from recreation. In order to improve water quality, restoration programs are implemented, including numerous methods. Intense nutrient cycling resulting from detrimental role of sediments impede obtaining of clear water state. One of the restoration methods proposed in recent years was Effective Microorganisms (EM), i.e. the set of microorganisms aiming at the inhibition of harmful bacteria through competitive exclusion. This approach was introduced in shallow Konin Lake (Western Poland), suffering from severe cyanobacterial water blooms. Prior to the treatment, protective action was conducted i.e. the elimination of external nutrient loads with backwater from the river. Changes in water chemistry, phytoplankton structure and macrophytes distribution were noted during the 5-year studies (2011-2015), covering the treatment (2013-2015) as well as two previous years. Oscillatoriacean cyanobacteria were most abundant in (2011-2012), while Nostocales in summer 2014-2015, as a result of decreased phosphorus but increased nitrogen concentrations. Slight increase in Cladoceran zooplankton was observed, but none in submerged macrophytes due to low water transparency. EM application initiated positive changes in the ecosystem by means of excessive organic matter decomposition and increased diversity of phytoplankton, nevertheless cyanobacteria blooms were still present due to high nutrient content.
Keywords: Backwater separation; Cyanobacteria; Lake restoration; Macrophytes; Nutrients.
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