Magnetic Fe3O4 nanoparticles enhance cyanobactericidal effect of allelopathic p-hydroxybenzoic acid on Microcystis aeruginosa by enhancing hydroxyl radical production.

Recently, considerable progress has been made in the environmental application of nanotechnology. However, little is known about how nanomaterials might affect the cyanobacterial suppression potential of allelochemicals. In this study, a microcosm was employed to simulate and verify the effect of magnetic Fe3O4 nanoparticles (MFN) on the inhibitory influence of allelopathic hydroxybenzoic acid (p-Ha) on bloom-forming Microcystis aeruginosa. MFN had a hormetic effect on cyanobacterial growth. At a neutral concentration of 182 mg/L, MFN enhanced the algal suppression by p-Ha and decreased the IC50 by half, which was significantly and positively associated with the amount of OH. Furthermore, adding MFN induced a stronger physiological response than treatment with only p-Ha. The cellular integrity was severely disrupted for the cyanobacterium M. aeruginosa. The total protein content decreased rapidly to inactivate the algae by limiting the amounts of extracellular microcystin and polysaccharide released. The modification of the effect of p-Ha by MFN was reflected by the intracellular NO content of M. aeruginosa. In addition, the typical radical scavengers ascorbic acid and 5,5-dimethyl-1-pyrroline N-oxide decreased OH production to weaken algal suppression under the combined treatment with p-Ha and MFN. By contrast, the addition of Fe3+ and increasing the light intensity triggered the generation of OH and strong cyanobacterial suppression. Thus, MFN could enhance the cyanobacterial control efficiency of p-Ha and decrease the input of allelochemicals in the field. These findings suggest a novel mode of allelochemical modification by nanomaterials as a promising cyanobactericide for harmful algal bloom management.

Allelopathy appraisal of worm metabolites in the synergistic effect between Limnodrilus hoffmeisteri and Potamogeton malaianus on algal suppression.

In Chinese Lake Taihu, the algal quantity was significantly larger in summer than late spring (p < 0.01). In summer, compared with the dredged area including neither zoobenthos nor submerged macrophytes, the algal biomass and density were significantly lower in the area filled with the submerged macrophytes. Interestingly, the minimum algal bloom was observed in the combined area containing submerged macrophytes and zoobenthos, which was due to the synergistic interaction between the zoobenthos and the macrophytes. The metabolite extracts from the numerically dominant zoobenthos Limnodrilus hoffmeisteri had significant algal inhibitory effects of Microcystis aeruginosa, and displayed stimulatory effects on seed germination, seedling growth, and peroxidase activity of the prevalent submerged macrophyte Potamogeton malaianus. 27 active compounds in the worm metabolites were identified by gas chromatography-mass spectrometry (GC-MS). Among these compounds three chemicals arachidonic acid, eicosapentaenoic acid, and linoleic acid with concentrations of 13.92 ±â€¯1.11, 10.57 ±â€¯2.52, 2.75 ±â€¯0.73 mg/kg dry weight, respectively, were confirmed as the typical allelochemicals with algal inhibition potential. In short, the metabolites allelopathy of L. hoffmeisteri can form and assist the synergistic effect between L. hoffmeisteri and P. malaianus on algal suppression. Thus, it is feasible to simultaneously restore submerged macrophytes and zoobenthos community in the disturbed eutrophic lakes for removing harmful algae.

Nano-fumed silica as a novel pollutant that inhibits the algicidal effect of p-hydroxybenzoic acid on Microcystis aeruginosa.

Nanomaterials and/or contaminants are becoming more common in the developing world, but their effects on interspecific interactions are rarely reported, particularly in aquatic ecosystems. Thus, the present study determined the effects of the novel pollutant nano-fumed silica (NFS) on algal control by a macrophyte via the allelochemical p-hydroxybenzoic acid in a microcosm test. The allelochemical p-hydroxybenzoic acid caused significant decreases in chlorophyll a, but increased the amount of superoxide anion radicals ( O2∙- ) and the electric conductivity in Microcystis aeruginosa. The 50% inhibitory concentration (IC50) for p-hydroxybenzoic acid was 0.919 mmol/L in microalga during the exponential phase. Interestingly, NFS at 100-1600 mg/L had clear stimulatory effects on M. aeruginosa. When NFS at 800 mg/L was combined with different concentrations of p-hydroxybenzoic acid, the IC50 for p-hydroxybenzoic acid was 1.045 mmol/L. Thus, NFS significantly reduced the algicidal effect exhibited by p-hydroxybenzoic acid on M. aeruginosa. Furthermore, NFS might act as a silicon nutrient and enhance allelopathic resistance in M. aeruginosa to inhibit the algicidal effects of macrophytes via allelopathy. These findings suggest that before algal control is considered using macrophyte allelopathy, it is essential to remove the pollutant NFS from polluted lakes.

Antialgal effects of five individual allelochemicals and their mixtures in low level pollution conditions.

An effective, environmentally friendly, and eco-sustainable approach for removing harmful microalgae is exploiting the allelopathic potential of aquatic macrophytes. In this study, we simulated field pollution conditions in the laboratory to investigate algal inhibition by allelochemicals, thereby providing insights into field practices. We tested five allelochemicals, i.e., coumarin, ρ-hydroxybenzoic acid, protocatechuic acid, stearic acid, and ρ-aminobenzenesulfonic acid, and a typical green alga, Chlorella pyrenoidosa, under two conditions. In the unpolluted treatment, individual allelochemicals had strong algal inhibition effects, where coumarin and ρ-hydroxybenzoic acid had greater potential for algal inhibition than protocatechuic acid, stearic acid, and ρ-aminobenzenesulfonic acid based on the 50 % inhibitory concentration. However, when two or three allelochemicals were mixed in specific proportions, the algal inhibition rate exceeded 80 %, thereby indicating allelopathic synergistic interactions. Mixtures of four or five allelochemicals had weak effects on algal inhibition, which indicated antagonistic interactions. Furthermore, the presence of low lead pollution significantly reduced the antialgal potential of individual allelochemicals, whereas the allelopathic synergistic interactions with mixtures between two or three allelochemicals were changed into antagonistic effects by low pollution. In particular, the allelopathic antagonistic interactions between four or five allelochemicals were increased by pollution. The allelopathic performance of these five allelochemicals may depend on various factors, such as the chemical species, mixture parameters, and algal strain. Thus, we found that low level pollution reduced the allelopathic inhibition of microalgae by allelochemicals. Therefore, the control of algae by the direct addition of allelochemicals should consider various environmental factors.

Combined effect of predatory zooplankton and allelopathic aquatic macrophytes on algal suppression.

The present study evaluated the combined effects of four typical predatory zooplankton and allelopathic aquatic macrophytes on algal control in a microcosm system. It would determine the effects of diverse species and biological restoration on the growth of harmful water-bloom microalgae in great lakes polluted by excess nutrients. It was found that the mixtures of each zooplankton and the floating plant Nymphoides peltatum had stronger inhibitory effects on harmful water-bloom microalgae than the individual species in clean or eutrophic water bodies. In addition, a community of four zooplankton types had a synergistic effect on algal inhibition. Algal suppression by the zooplankton community was enhanced significantly when the macrophyte was co-cultured in the microcosm. Furthermore, Chlorella pyrenoidosa was more susceptible than Microcystis aeruginosa when exposed to grazing by zooplankton and the allelopathic potential of the macrophyte. Algal inhibition was also weaker in eutrophic conditions compared with the control. These findings indicate that diverse species may enhance algal inhibition. Therefore, it is necessary to restore biological diversity and rebuild an ecologically balanced food chain or web to facilitate the control of harmful algal blooms in eutrophic lakes.

Environmental monitoring and assessment of the water bodies of a pre-construction urban wetland.

It is planned that the Dayanghan Wetland in China will be transformed into a national park but little is known about its current water quality and pollution status. Thus, we monitored the physical and chemical characteristics of the Dayanghan Wetland, which showed that the water quality was generally good. However, the chemical oxygen demand was more than double the reference value, which may be attributable to previous tillage for vegetable crops and other farmlands. In addition, nickel and chromium caused low-level pollution in the water bodies of the Dayanghan Wetland. The mean trophic level index and nutrient quality index were 39.1 and 2.69, respectively. Both indices suggest that the water bodies of the Dayanghan Wetland are in a mesotrophic state and that no eutrophication has occurred. The study would provide a precise report on the status of environmental quality of the water bodies of a typical pre-construction wetland for the administration and decision of the local government and the planning agent.

Algicidal effects of four Chinese herb extracts on bloom-forming Microcystis aeruginosa and Chlorella pyrenoidosa.

Extracts from four Chinese herbs, Phellodendri chinensis cortex, Artemisia annua L., Scutellaria baicalensis G. and Citrus reticulate peel were tested for their algicidal effects on Microcystis aeruginosa and Chlorella pyrenoidosa. The results showed that M. aeruginosa was more susceptible than C. pyrenoidosa. The growth of M. aeruginosa was significantly inhibited (p < 0.05) by the four herb extracts. Among the four herbs, P. chinensis cortex and S. baicalensis had the greatest inhibitory effects on M. aeruginosa, followed by C reticulate peel and A. annua. The 50% effective concentrations (EC50) of S. baicalensis, P chinensis cortex, C. reticulate peel and A. annua were 0.87, 0.88, 5.27 and 1 1.16 gherb L-1, respectively. The growth of C. pyrenoidosa was moderately inhibited by the herb extracts individually. The EC5o concentrations for S. baicalensis, P. chinensis cortex, C. reticulate peel andA. annua were 8.67, 11.67, 12.81 and 12.44 g herb L-1', respectively. Extract from S. baicalensis displayed stronger algicidal effects on C. pyrenoidosa than the other three herbs, although no lethal effect on C. pyrenoidosa was observed during the cultivation period. Compared with corresponding individual extract at the same dosage, the binary mixtures of the four herb extracts enhanced the algicidal effects on M. aeruginosa. The maximum inhibitory rates of all binary mixtures of the four herb extracts were all above 92% during the 10-day incubation. The results demonstrate that Chinese herbs, such as P. chinensis cortex or S. baicalensis and their combinations, could offer an effective alternative for mitigating outbreaks of harmful algal blooms in water bodies.