Sustainable approach to lake restoration – an innovative treatment applied in Polish lakes

A sustainable strategy, involving a combination of physical, chemical and biological methods was proposed as an innovative approach to lake restoration in Poland. We believe that: (i) the interference with the lake shall be limited to the extent that is necessary for the gradual reconstruction of the ecosystem; (ii) attention must be paid to the preservation of biodiversity as an important element affecting the adaptation of the ecosystem in the face of change; and (iii) restoration requires less invasive methods (in comparison with eg. sediment dredging) and nature-based solutions. In the sustainable approach combined methods are used simultaneously, i.e. physical (hypolimnion aeration by means of wind-driven aerator), chemical (phosphorus and ammonium N precipitation with small doses of compounds) and biological methods (supportive stocking with the fry of predatory species). Another innovative method is the direction of spring waters containing high concentrations of nitrates to the deoxygenated bottom of the lake. This method increased the redox potential in the sediment-water interface, preventing the release of phosphorus from the bottom to the water column. It should be stressed that all methods are cost effective compared to other methods of restoration, what is of paramount importance for the local administration, being usually sponsors of lake restoration in Poland.

Long-term studies conducted in several lakes indicated a gradual improvement of water quality by means of: (i) reduction of phosphorus content, (ii) a decrease in chlorophyll-a concentration coupled with an increase of water transparency, (iii) rebuilding the species composition in phytoplankton community (replacement of Cyanobacteria by other groups of algae.