The sustainable restoration of lakes—towards the challenges of the Water Framework Directive

Most in-lake restoration projects use deeply intrusive methods. They include the removal of bottom sediments and the use of high doses of precipitants. They are very radical, causing extinction of many organisms, and are very expensive. Alternative methods described in this paper are inexpensive, easy to use, effective, and sustainable (energy-efficient, not destructive for most of the biota). They have been applied to three lakes located in Poznań and the surrounding area (Western Poland) and their effectiveness has been documented. They include: (i) use of biomanipulation to increase trophic influence of zooplankton on phytoplankton, and small doses of iron sulphate to reduce phosphorus content in the water column, used in Maltański Reservoir, (ii) delivering water rich in nitrates from small tributaries to the deepest part of the lake, thus increasing redox potential and limiting the release of phosphorus from bottom sediments, used in Uzarzewskie Lake, (iii) oxygenation of hypolimnetic waters using wind aerators, iron treatment with small doses of coagulant and biomanipulation, used in Durowskie Lake. Use of limited doses of an innovative solid phosphorus precipitant called Sinobent® is also possible. These methods, in accordance with the intermediate disturbance hypothesis, increased the diversity of flora and fauna in the lakes and contributed to improvements in water quality. Simultaneous application of several methods, which prevented feedback mechanisms, increased the efficiency of lake restoration.