Sustainable Restoration as a Tool for the Improvement of Water Quality in a Shallow, Hypertrophic Lake

Abstract

Sustainable restoration treatments were implemented with the simultaneous application of pro-ecological methods that complement each other to improve water quality in the shallow and heavily polluted Raczyńskie Lake. Phosphorus inactivation with magnesium chloride and Phoslock® was introduced along with biomanipulation. Physico-chemical and biological parameters were studied in 2015 (before restoration) and throughout 2018 and 2019 (during restoration). Water quality improved in the first year of treatment. An increase in water transparency, oxygen concentration above the bottom, a decrease of chlorophyll-a concentration and a reduction in cyanobacteria were observed. In the second year of treatment, a slight deterioration of water quality was recorded, probably caused by fewer phosphorus inactivation treatments and a shortened period of application. However, the deterioration of conditions is also characteristic of sustainable restoration at the beginning of the restoration process. The obtained results showed that sustainable restoration requires more than two years, and its scope and intensity should strictly depend on the pace of changes, determined on the basis of monitoring. In addition, improved water quality will have a positive impact on the recreational use of this reservoir.