Long-Term Changes in the Trophic State of Suwalki Lakes—An Analysis by Means of Indices Based on Abundance and Composition of Their Rotifer Fauna

Rotifer abundance and species composition in lakes of the Suwalki Landscape Park were studied in the years 1983–1985, 2009, 2012 and 2015. Rotifer trophic state indices (TSI_ROT) were used to assess changes in the trophic state of the studied lakes. In most lakes of the Suwalki Landscape Park, there were no changes in rotifer communities over the 25–32 year period to indicate a decline in trophy of the lakes. However, in lakes with the strongest decline in TSI_ROT values, the values of indicative parameters widely varied in 2015, which may indicate that the status of rotifer communities in the lakes may be dependent on non-trophic factors.