Stability and Diversity in Lake Ecosystem Two Decades after Restoration

Lake Piskory is situated in central-eastern (CE) Poland, in the southeastern part of the Vistula River spillway about 7.5 km from the mouth of the Wieprz River to the Vistula River. Prior to 1993 when restoration activities aimed at reestablishing hydrological function and diversifying habitats were implemented, the area was overgrown with rush vegetation and the water mirror seized to exist. In the initial years post restoration, the lake surface area increased and plant diversity grew. However, since 2000 plant diversity has decreased largely due to the rapid growth of Carex and Phragmites, and the lake is once again being overgrown. Here we document changes in vegetation and water hydro-chemical features from 1993 to 2015 and compare land-use activities from 1973 to 2015 to better understand the causes and implications of these changes. The surface area of the lake varied throughout monitoring years, particular plant communities fluctuated, from 2005 to 2010. During dry years the area of reed rushes visibly grew, while the extent of valuable underwater stonewort meadows contracted and disappeared. Man-made ecosystems often require continuous management action. If active management is not taken in the Lake Piskory region, complete overgrowth of the system is once again possible and the system may transition into a novel ecological status.