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Sediment cores were collected from the Xiangxi River, a tributary of the Three Gorges Reservoir, the deposition time in the longest sediment core (90 cm) was measured by radiometry (137Cs, 210Pb) activities and polychlorinated dibenzo-p-dioxins/furan (PCDD/F) concentrations in different depths of the sediment core were measured. The results indicated that the mean deposition rate was 1.01 cm/a. The total PCDD/F concentrations ranged from 19.28 to 70.07 pg/g d.w. with a mean of 35.06 pg/g d.w. PCDD/Fs in the 1960–1990s were higher than others, which were significantly different in the various layers and cores (p < 0.05). PCDD occupied 63.42–87.33% of PCDD/Fs, and octachlorianted debenzo-p-dioxin (OCDD) was the predominant congener. The ratio of PCDD to PCDF was 2.26–8.08. PCDD/Fs significantly correlated with total organic carbon (TOC) (p < 0.01). The toxic equivalent (TEQ) ranged from 0.15 to 0.98 pg/g d.w. No significant difference was found in TEQ (p > 0.05). It was concluded that the spatio-temporal heterogeneity determined by hydrodynamics and total organic carbon (TOC) was the distribution pattern of PCDD/Fs in the sediment cores of Xiangxi River, the concentrations of PCDD/Fs were low, with a low environmental pollution risk, and by-products of sodium pentachlorophenate might be the main source. [ABSTRACT FROM AUTHOR]

An investigation was conducted in the Three Gorges Reservoir (TGR) seasonally from September 2010 to June 2011 to screen the distribution pattern of suspended particulate matter (SPM). Concentration of SPM, particulate nitrogen (PN), particulate phosphorus (PP), bioavailable particulate phosphorus (BAPP), and chlorophyll a (Chl a) were determined synchronously. Concentration of SPM was higher in the flood season than in the dry season and higher in the mainstream than in the tributaries. Chl a, PN, PP, and BAPP showed similar temporal pattern with SPM distribution. Particulate elements were significantly correlated with concentrations of SPM ( p < 0.05). The proportion of algae-derived SPM in total SPM was higher in the tributaries than that in the mainstream. The results revealed that the spatiotemporal heterogeneity determined by hydrodynamics was the characteristic of SPM distribution. The source of SPM was mostly allochthonous. It could be deduced that SPM was an important factor affecting the water quality and algal growth in TGR by releasing or absorbing particulate nutrient. [ABSTRACT FROM AUTHOR]

Simulation studies on decline phase of Microcystis blooms were carried out in Xiangxi River between 31 July and 28 August, 2009. Relationships between Microcystis cell density (MCD) and environmental parameters were analyzed, and the morphophysiological changes of Microcystis were described in the present research. Results showed that total phosphorus, ammonia-nitrogen, dissolved oxygen, turbidity, conductivity and pH significantly affected the MCD, respectively, but water temperature was negatively correlated (p<0.0l) with MCD. During the decline phase, Microcystis cellular carbohydrate and protein contents decreased, and the large colonies ruptured into small ones which accelerated by raining interference. Meanwhile, most of Microcystis cells were dead, leaving only few living cells. Since water temperature (ranging from 26.4 to 29.3 °C) increased gradually and was higher than the suitable growth temperature for Microcystis in the whole experiment, it was concluded that shorterm dynamics of Microcystis resulted from changes of multiple environmental parameters rather than the water temperature. Simultaneously, recruitment was considered to contribute little to the formation of Microcystis blooms in Xiangxi River for the remaining living cells which would further decay in the sediment during the over-wintering periods. The present study also demonstrated the convenience of using the in situ enclosures to study the eco-physiological changes of algae. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H 2 O 2 ) is a widely accepted algicide in controlling cyanobacterial blooms. However, this method includes two disadvantages: 1) a low H 2 O 2 concentration (<5 mg L -1 ) is required; 2) H 2 O 2 -induced cell lysis causes phosphorus (P) contamination. To overcome the drawbacks, a H 2 O 2 slow-releasing composite (HSRC) based on calcium peroxide (CaO 2 ) was fabricated to substitute liquid H 2 O 2 . According to the results, a higher CaO 2 dose increased H 2 O 2 yield and releasing rate. H 2 O 2 yield of 160 mg L -1 CaO 2 in HSRC reached 32.9 mg L -1 and its releasing rate was 0.407 h -1 . In addition, a higher temperature decreased H 2 O 2 yield and increased H 2 O 2 -releasing rate. Besides, HSRC endowed with a remarkable ability to immobilize P. Higher CaO 2 dose, pH value, and temperature increased the rate of P immobilization. The highest rate was 0.185 h -1 , which occurred with 160 mg L -1 CaO 2 in HSRC at 25 °C and pH 8.0. Toxicity assays showed that HSRC exerted sustaining oxidative stress on Microcystis aeruginosa. Accumulation of intracellular reactive oxygen species resulted in the disruption of enzymatic systems and inactivation of photosystem. Tracking the variations of cell growth and H 2 O 2 concentration during HSRC treatments, it suggested that the lethal effect on Microcystis aeruginosa was achieved with a super-low H 2 O 2 concentration (<0.3 mg L -1 ). In addition, cell lysis did not cause a sudden rise in P concentration due to the P immobilization by HSRC. Therefore, HSRC successfully offsets the drawbacks of liquid H 2 O 2 in mitigating cyanobacterial blooms. It may be a novel and promising algicide that not only kills cyanobacteria but also reduces eutrophication momentarily., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)