To control harmful algae blooms (HABs), methods based on natural mechanisms are now required. We investigated the effects of an algicide derived from macrophyte metabolites, namely mixtures of gallic, tetradecanoic, heptanoic, and octanoic acids (1:1:1:1 mass ratio, a total concentration of 14 mg/L), on the biomass of cyanobacteria and other plankton and the production of microcystins under experimental conditions. Two types of microcosms have been created: simple (microalgae, cyanobacteria, and zooplankton) and complex (microalgae, cyanobacteria, zooplankton, and planktivorous fish). We observed the dynamics of the phytoplankton structure, the concentrations of microcystins and chlorophyll-a, hydrochemistry, and the status of zooplankton and fish in both types of microcosms with and without algicide for one month (from 19 July to 19 August 2021). The introduction of algicide caused changes in phytoplankton structure, a drop in cyanobacterial biomass, and a decrease in the total concentration of microcystins. Surprisingly, the contributions of the most toxic microcystins (LR form) were higher in both types of microcosms exposed to algicide than in microcosms without algicide. The inhibitory effect on the cyanobacterial biomass was most significant in complex ecosystems (containing fish), while it was only observed at the end of the exposure in simple ecosystems. Not only algicide but also phytoplankton consumed by fish and zooplankton, as well as nutrient excretory activity by both consumers, seem to have impact on cyanobacterial biomass. This study found that the using chemical substances similar to macrophyte metabolites can help regulate HABs and cyanotoxins. However, the results differ depending on ecosystem type.

Cyanobacteria, which develop abundantly in aquatic ecosystems, can be harmful to humans and animals not only by releasing toxins that cause poisoning but also by provoking cytogenetic effects. The influence of the mass development of cyanobacteria on the genotoxic properties of natural water has been studied in model ecosystems (microcosms) with different compositions of biotic components (zooplankton, amphipods and fish). The validated plant test system “Allium test” was used in this study. Genotoxic effects were detected at microcystin concentrations below those established by the World Health Organization (WHO) for drinking water. In all experimental treatments, cells with disorders such as polyploidy and mitotic abnormalities associated with damage to the mitotic spindle, including c-mitosis, as well as lagging chromosomes were found. Genotoxic effects were associated with the abundance of cyanobacteria, which, in turn, depended on the composition of aquatic organisms in the experimental ecosystem. Fish, to a greater extent than other aquatic animals, maintain an abundance of cyanobacteria. After one month, in microcosms with fish, mitotic abnormalities and polyploidy continued to be detected, whereas in other treatments, there were no statistically significant genotoxic effects. In microcosms with amphipods, the number and biomass of cyanobacteria decreased to the greatest extent, and only one parameter of genotoxic activity (frequency of polyploidy) significantly differed from the control.

The intensity of oxygen consumption and the rate of phosphorus excretion are studied in planktonic crustaceans Daphnia longispina O.F. Müller (Cladocera), benthic crustaceans Hyalella azteca (Saussure) (Amphipoda), and fish Oryzias latipes (Temminck & Schlegel) (Beloniformes) united in one trophic net in an experimental ecosystem. The highest rates of metabolic intensity are established for small organisms Daphnia longispina (7.44 ± 2.49 mgO/(g h) and 0.447 ± 0.143 mgP/(g h)). The rate of phosphorus excretion differed by an order of magnitude between hydrobionts of different ecological groups and decreased in the order planktonic crustaceans –> benthic crustaceans –> fish. It is shown that the contribution of hydrobionts to the creation of primary production depends on the biomass of a particular species.

Aquatic vascular plants at different stages of their life cycle exhibit different physiological and metabolic activity, resulting in a change in habitat conditions for hydrobionts. The hydrochemical parameters of the environment, the concentrations of phytoplankton pigments, and the abundance of bacteria and zooplankton have been studied in experimental ecosystems (microcosms), including aquatic plants going through varying degrees of decomposition. In microcosms with hornwort Ceratophyllum demersum L., which lost half of the biomass, but continued vegetation, the concentration of P_tot, Mg²⁺, and BOD₅ increase and Na⁺ and Ca²⁺ decrease. In systems with dying arrowhead Sagittaria sagittifolia L., the concentration of K⁺ increases to the greatest extent and P_tot, Cl^–, and BOD₅ to a lesser extent; the concentrations of S\({\text{O}}_{4}^{{2 - }}\) and O₂ dissolved in water decrease. In the presence of plants, higher concentrations of phytoplankton pigments are observed compared to the control. The quantitative parameters of bacterioplankton do not differ. The abundance and biomass of zooplankton in general and of the dominant species Daphnia longispina in microcosms with plants exceed these control parameters. Hornworts, which lose half of their biomass but continue vegetation, have a stronger stimulating effect on the abundance of zooplankton than arrowheads, which finish vegetation

Cyanobacterial blooms in aquatic ecosystems are a major global environmental concern. While the mutagenic and mitosis-disrupting properties of isolated cyanobacterial toxins are well documented, evidence of cytogenotoxic effects resulting from cyanobacterial blooms in natural aquatic ecosystems remains limited. In this study, water genotoxicity was evaluated in microcosms simulating cyanobacterial blooms of varying abundance. In microcosms with initially high cyanobacterial abundances (4.6 × 10⁷ and 2.2 × 10⁷ cells L⁻¹) and biomass (58 mg L⁻¹ and 20 mg L⁻¹), significant toxic, cytotoxic, mitosis-disrupting, and mutagenic effects were observed: root elongation was inhibited by up to 49.6% (Day 1), the mitotic index decreased by ~33% (Treatment I, Day 42) vs. Control, and total chromosomal aberrations and lagging chromosomes increased by ~2.5-fold on Day 1 (Treatment I) and ~4.7-fold on Day 42 (Treatment I) vs. Control; micronuclei increased ~10-fold on Day 42 in Treatment I and II. In microcosms with lower cyanobacterial abundance (1.2 × 10⁷ cells L⁻¹) and biomass (9 mg L⁻¹), significant reductions were observed only in root growth and in the mitotic index compared with Control. Future research should aim to identify a broader spectrum of cyanobacterial toxins and to investigate their environmental fate and persistence in aquatic ecosystems, particularly since genotoxic effects were detected even during the post-bloom period: on Day 42 extracellular microcystins in water were <LOQ in Treatments I and III (and 0.025 µg L⁻¹ in Treatment II), yet chromosome lagging and micronuclei remained elevated. The observed genotoxicity associated with cyanobacterial metabolites underscores the need for thorough risk assessments of cyanobacterial blooms in aquatic environments.

The effect of tris(chloropropyl)phosphate (TCPP), an organophosphorus ester, at concentrations of 100, 500, and 1000 nanograms per liter (ng/L) on the growth of the aquatic plant Lemna minor was studied. The effect of TCPP on the population size of L. minor has been found. A higher specific growth rate, as well as the appearance of more fronds by the end of the experiment were detected in the medium with the lowest concentration of TCPP. At the highest concentration of TCPP, the daughter fronds failed to separate from the mother plant, leading to the formation of large colonies. The number of fronds within these colonies could reach as high as 18. As a result, the actual production of the L. minor population was lower than the potential one due to the lack of maternal fronds to produce new plants.