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CHANGES OF PHYSICAL AND CHEMICAL FEATURES OF WATER UNDER THE INFLUENCE OF IRON COAGULANT IN NATURAL CHAROPHYTES COMMUNITIES

Michał Rybak

Abstract

The iron phosphates coagulant is commonly used in lake restoration to improve water quality and eliminate cyanobacteria bloom. Nevertheless, the short-term abiotic environment transformation in particular inside macrophytes communities is still not sufficiently studied. The field experiments were carried out in mesocosms installed in Chara hispida community. This species is characteristic for eutrophic lakes, therefore is strongly vulnerable to restoration treatments. In the study five parameters were analysed: pH, conductivity, alkalinity, turbidity and water colour under influence of iron sulphate in three different concentrations (76.7; 153.5 and 307.0 g m-2). Application of coagulant caused a strong, however temporary changes in chemical and physical features of water. The environment modification was proportional to the coagulant concentration. After coagulant application, pH decreased immediately and slight water acidification was observed. Iron sulphate dissociation in water caused increase of ions concentration and thereafter higher conductivity. This was the only one parameter which was elevated until the end of experiment. Increased of water colour directly referred to dark brown colour of iron sulphate and was followed by turbidity increased. Changes in alkalinity were not observed. All transformations were neutralised during first 48 hours and were tightly connected with a coagulation and flocculation processes. Coagulant application trigger short-term modifications, nonetheless far-reaching consequences. Firstly, acidification changes abiotic environment preferred by charophytes and led to increased solubility and toxicity of metal ions. Secondly, implementation of additional ions origin from coagulant caused collapse in ions equilibrium in water. Finally, water colour and turbidity transformations generate disturbances in light availability for plants. Consequently, seemingly negligible changes in abiotic environment may have in fact essential influence on biota, which have to been taken into account during restoration treatments programme.

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DOI resolver: doi.org/10.5593/sgem2018/5.2/s20.024

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