Key speakers

Piotr Klimaszyk is an associated professor at Adam Mickiewicz University in Poznań. He is a Head of the Department of Water Protection at Faculty of Biology AMU. Since the beginning of his scientific career he has been interested in the interactions between aquatic and terrestrial ecosystems. Initially he studied the functioning of ponds and small bodies of water in different types of landscape, the role of surface runoff in shaping the trophic state of lakes and the influence of waterbirds on the translocation of nutrients between aquatic and terrestrial ecosystems. During his scientific internship in Kazakhstan, he participated in research on the changes in the biotope and biocenoses of the Aral Sea. His current interests include aquatic ecotoxicology and lake restoration ecology. He is a member of the Drawa National Park Advisory Board and, since 2021, President of the Polish Limnological Society.

DARK SIDE OF CHEMICAL RESTORATION OF LAKES

Klimaszyk Piotr, Rybak Michał, Joniak Tomasz, Drewek Agnieszka
Department of Water Protection, Adam Mickiewicz University Poznań, Poland

In Europe more than 50% of the water bodies are in a bad ecological and chemical state, and in Central Europe estimates show that even over 80% are seriously polluted. The problem of deteriorating aquatic ecosystems quality has raised worldwide concerns and has resulted in national and international law regulations to protect and restore water resources. According to Water Framework Directive, all water ecosystems in European Union countries should achieve good ecological status by 2027. To improve freshwater ecosystems' quality and ecological status, it is necessary to apply effective restoration methods. These methods are very diverse, ranging from biological that alter ecosystem food chains, through technical methods - supplying oxygen to deep layers of lakes or removing bottom sediments, to chemical methods that alter biogeochemical processes. Often a combination of several methods is used simultaneously, however their primary goal is to stimulate re-oligotrophization processes. Among the chemical methods the introduction of acidic solutions of iron (Fe) or aluminum (Al) salts, which bind phosphates into complex compounds is very common. Chemical inactivation of phosphorus results in almost immediate improvements in water quality at relatively low cost. However, the effects of coagulants are not always predictable, and the magnitude of ecosystem hazards is not fully understood. The use of the coagulants results in physical and chemical transformations, which lead to short-term acidification, deterioration of optical water properties and sedimentation of aggregates-flocks. We found the changes in functional traits of charophytes and macrophytes (relative growth rate inhibition, stem, leaves and roots mass reduction or photosynthetic surface area augmentation through the development of branchlets and side-branches) treated with coagulants. The response is species-depend. High coagulant concentration create the possibility of plant death. Acidification also contributes to the dissolution of the carbonate encrustation covering the charophytes and imbalance the calcium budget in the ecosystem (in sulphate compounds). Elimination of bioavailable phosphates and excess of Fe or Al ions has consequences in the disruption of ecological homeostasis resulting in the C: N: P ratio change and metal ions accumulation. In the case of consumers, experimental studies show that Fe and Al-based coagulants may disrupt embryonic development and reduce the reproductive success of pike – species of particular interest for biomanipulation – top-down regulation. In the mussels, filter feeders essential for the ecosystem health, disturbances in filtration rate, with closing time extension, starting immediately after coagulant application were observed. Acidification and the environmental elemental composition changes lead to the metal ions accumulation and reduction of phosphorus and calcium content in the mussels bodies.

Keywords: eutrophication, phosphorus, lakes restoration, aluminum coagulant, iron coagulant, adverse effects