Changes in Chara hispida L. morphology in response to phosphate aluminium coagulant application

Abstract

Progressing eutrophication of waterbodies requires measures to be undertaken that aim at halting or reversing negative changes in the environment. Chemical restoration is one of the most common methods used for lake treatment, where iron or aluminium phosphate coagulants are applied. However, their chemical qualities pose the risk of acidification and aluminium ion release, which become toxic in acidic conditions. The influence of coagulants on aquatic plants, including charophytes that are very valuable from the ecological perspective, is little recognised. For this reason, the aim of the research was to define changes in the growth pattern of the charophyte Chara hispida under the influence of an aluminium coagulant. The research was carried out in mesocosms (0.8 m3) located in situ in a lake. Polyaluminium chloride was applied once to each chamber in doses of 50.0, 100.0 and 200.0 ml m−3. Coagulant concentrations reflected aggressive restoration aimed at precipitation of phosphates, suspension and water colour at the same time. It was proved that the coagulant had inhibited the growth and slightly reduced the length of branchlets, and simultaneously elongated internode cells. Changes in the total length as well as the length of branchlets were caused by a strong pH decrease of the environment which simultaneously induced higher aluminium solubility and toxicity. Elongation of internode cells was caused by reduced light availability, resulting from high water turbidity in the first stage of coagulant’s application, and then from the charophytes’ thallus being covered by a coagulated suspension precipitated from water.

Were there any changes in zooplankton communities due to the limitation of restoration treatments?

“…Iron sulphate and magnesium chloride causes precipitation of phosphorus from the water column, limiting the phytoplankton growth, especially cyanobacteria. The use of high doses of precipitants brings faster effect but may pose a threat to aquatic organisms (Immers et al 2014;Rybak et al 2020;Rybak and Joniak 2018). Thus sustainable restoration is based on repeated application of low doses of chemicals .…”

Sustainable lake restoration: From challenges to solutions

“…However, extreme caution must be exercised when adding excess N to eutrophic systems to avoid causing secondary problems, such as unintended proliferation of non‐N‐fixing, toxin‐producing cyanobacterial taxa (Paerl et al, 2016). Environmental concerns regarding chemical treatments also include potential harmful effects on flora and fauna, and thus ecotoxicological tests are needed before broad application (Drewek et al, 2022; Lürling, Smolders, & Douglas, 2020; Rybak & Joniak, 2018). Nature‐based interventions that maximize ecosystem services (Triest et al, 2016) could provide safer solutions in the context of environmental risks too (Dondajewska et al, 2019).…”