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To investigate the relationship between cyanobacteria decomposition and the remobilization of heavy metals in Taihu Lake, the indoor simulation experiments were conducted. The areas of Taihu Lake that undergo harmful algal blooms mostly caused by excessive cyanobacteria have serious problems of heavy metal pollution. The results showed that cyanobacteria decomposition can release heavy metals into the water and change the total contents and chemical speciation of Cr, Ni, Cu, Zn, As, Cd, Hg, and Pb in sediment due to the change of physical and chemical properties in overlying water and sediment. The decomposition rate of cyanobacteria with sediment was clearly faster than that without sediment, and decomposition changed the pH and dissolved oxygen (DO) concentrations in overlying water. The cyanobacteria decomposition reduced the oxidation-reduction potential (ORP), and increased organic matter (OM) and total organic carbon (TOC) in the surface sediment. According to ecological risk assessment, the cyanobacteria decomposition increased the degree of heavy metal pollution and the potential ecological risk in sediment.

Environment-friendly algaecides based on allelopathy have been extensively studied to control harmful algal blooms (HABs). The inhibitory effects of linoleic acid (LA) sustained-release microspheres on different cell densities of Microcystis aeruginosa (M. aeruginosa) at different growth phases were studied. The results showed that the growth of M. aeruginosa could be inhibited within 4 days and the constant inhibitory rate with initial algal density of 8 × 105 cells∙mL−1 (exponential phase) was up to 96% compared with control. The chlorophyll-a content in the treatment group had the same change trend with the algal density and declined significantly at day 20th, which suggested that the microspheres could promote the degradation of chlorophyll-a. The activities of superoxide dismutase (SOD) and catalase (CAT) increased gradually within 5 days but then declined sharply, which indicated that LA microspheres could cause oxidative damage to M. aeruginosa during the process of inhibition and reduce the activities of antioxidant enzymes. In addition, the concentration of oxygen free radical (O2−) increased at day 10th and rose constantly, and the content of malodialdehyde (MDA) increased to 2.7 times as much as control at day 20th. Furthermore, the content of protein, nucleic acid and the conductivity in culture solution showed a significant rise. These results showed that algal cell membrane lipid peroxidation occurred and the membrane permeability increased, accompanied by the damage of cell membrane. To sum up, the destruction of algal cell membrane is the main mechanism of LA microspheres inhibiting algal growth.

This paper focuses on the characterization of extracellular polymeric substances (EPS), which are composed of soluble EPS (SL-EPS), loosely bound EPS (LB-EPS), and tightly bound EPS (TB-EPS) produced by Microcystis aeruginosa under the stress of linoleic acid (LA) and LA sustained-release microspheres. Three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy and Fourier transform infrared (FTIR) spectrometry were used to characterize three forms of EPS while the content of polysaccharide and protein was tested, respectively. The results showed that the highest inhibitor rate (IR) occurred when M. aeruginosa were exposed to LA sustained-release microspheres of 0.3 g L-1. The 3D-EEM contour demonstrated that tryptophan and protein-like substances were detected in all three EPS fractions, whereas humic acid-like substance was only distributed in SL-EPS, and aromatic proteins merely existed in LB-EPS and TB-EPS. The infrared spectrum showed that functional groups in three EPS fractions had no obvious change in all experimental groups. Polysaccharide (1120-1270 cm-1, C-O-C and C-O stretching vibration) and protein (1384-1670 cm-1, C-N and N-H stretching) were detected in three forms of EPS. Graphical abstract ᅟ.