Effect of suspended particulate matter on physiological, biochemical and photosynthetic characteristics of Chlorella pyrenoidosa in the Jinjiang Estuary (Fujian, China).

Suspended particulate matter (SPM), an important component of the natural water environment, can act as a carrier of many pollutants that affect aquatic organisms. In the present study, the effect of SPM obtained from Jinjiang Estuary on the physiological, biochemical, and photosynthetic properties of typical freshwater algae (Chlorella pyrenoidosa) was investigated. The results showed that under different concentrations of SPM treatment, the superoxide dismutase (SOD), catalase (CAT) activities, and malondialdehyde (MDA) content of C. pyrenoidosa increased, but the soluble protein content decreased. SPM with different particle sizes had less effect on SOD of C. pyrenoidosa, but showed a promoting effect on CAT and MDA as well as soluble protein content. In terms of photosynthetic activity, high concentrations (70, 90 mg/L) and small particle sizes (0-75, 75-120 µm) of SPM had a greater effect on the chlorophyll a content of C. pyrenoidosa. In addition, different concentrations of SPM had no significant effect on the potential photosynthetic activity of PS II (Fv/F0) and the maximum quantum yield of PS II (Fv/Fm), but the inhibition of the initial slope (alpha), the maximum photosynthetic rate (ETRmax) and the semi-light saturation point (Ik) increased with the increase of SPM concentration. Fv/F0, ETRmax, and Ik of C. pyrenoidosa showed some degree of recovery after inhibition in the presence of SPM of different particle sizes.

Effects of suspended particles in the Jinjiang River Estuary on the physiological and biochemical characteristics of Microcystis flos-aquae.

The effects of different concentrations (100, 150, 200, 250 mg/L) and different particle sizes (0-75 µm, 75-120 µm, 120-150 µm, 150-500 µm) on the soluble protein content, superoxide dismutase (SOD) and catalase (CAT) activity, malondialdehyde (MDA) content, chlorophyll a (Chla) content, and photosynthetic parameters of Microcystis flos-aquae were studied, and the mechanism of the effect of suspended particulate matter on the physiology and biochemistry of Microcystis flos-aquae was discussed. The results showed that the soluble protein content of Microcystis flos-aquae did not change noticeably after being stressed by suspended particles of different concentrations/diameters. The SOD activity of Microcystis flos-aquae first increased and then decreased with increasing suspended particulate matter concentrations. The SOD activity of Microcystis flos-aquae reached 28.03 U/mL when the concentration of suspended particulate matter was 100 mg/L. The CAT activity of Microcystis flos-aquae increased with increasing concentrations of suspended particles and reached a maximum value of 12.45 U/mg prot in the 250 mg/L concentration group, showing a certain dose effect. Small particles had a more significant effect on SOD, CAT, and MDA in Microcystis flos-aquae than large particles. The larger the concentration was and the smaller the particle size was, the stronger the attenuation of light and the lower the content of Chla. Both the maximum quantum yield of PSII (Fv/Fm) and the potential photosynthetic activity of PSII (Fv/F0) of Microcystis flos-aquae increased at first and then decreased under different concentrations/sizes of suspended particles. The relative electron transfer rate gradually returned to a normal level over time. There was no significant difference in the initial slope (α) value between the treatment group and the control group, and the maximum photo synthetic rate (ETRmax) and the semilight saturation (Ik) decreased.

Distribution characteristics of microplastics in the soil of mangrove restoration wetland and the effects of microplastics on soil characteristics.

The dense vegetation in the wetland could effectively retain microplastic particles, and the distribution of microplastics varied significantly under different planting densities. In addition, microplastics in the soil environment can affect soil properties to a certain extent, which in turn can affect soil functions and biodiversity. In this study, we investigated the distribution of soil microplastics in a mangrove restoration wetland under different planting densities and their effects on wetland soil properties. The results indicated that the average abundance of soil microplastics was 2177.5 n/500 g, of which 70.9% exhibited a diameter ranging from 0.038-0.05 mm, while the remaining soil microplastics accounted for less than 20% of all microplastics, indicating that smaller-diameter microplastics were more likely to accumulate in wetland soil. The microplastic abundance could be ranked based on the planting density as follows: 0.5 × 0.5 m > 1.0 × 0.5 m > 1.0 × 1.0 m > control area. Raman spectroscopy revealed that the predominant microplastic categories in this region included polyethylene terephthalate (PET, 52%), polyethylene (PE, 24%) and polypropylene (PP, 15%). Scanning electron microscopy (SEM) images revealed fractures and tears on the surface of microplastics. EDS energy spectra indicated a large amount of metal elements on the surface of microplastics. Due to the adsorptive features of PET, this substance could influence the soil particle size distribution and thus the soil structure. All physicochemical factors, except for the soil pH, were significantly affected by PET. In addition, the CV analysis results indicated that soils in vegetated areas are more susceptible to PET than are soils in bare ground areas, leading to greater variation in their properties.