Vallisneria natans is a submerged plant that is commonly used in ecological restoration programs. However, the effects of hydraulic disturbance and changes in water levels on the growth of this plant and the quality of water bodies have yet to be sufficiently established. In this study, we examined the effects of single and combined hydrodynamic stresses on the physiological and biochemical characteristics of bitter grass and water quality based on controlled experiments assessing different water levels (45 and 80 cm) and disturbance durations (4 and 8 h). The results indicated that high water levels with short-term disturbance (80 cm, 4 h) were associated with significant increases in the contents of dissolved oxygen to 9.1 mg/L (11.0% higher than that under non-disturbed conditions), and effectively reduced the concentrations of total nitrogen (1.85 mg/L), ammonia-nitrogen (0.20 mg/L), and nitrate-nitrogen (0.19 mg/L), while maintaining the lowest oxidative stress levels (peroxidase activity: 5.73 U/(g·min), superoxide dismutase activity: 17.6 U/g) and highest chlorophyll content (8.98 mg/g). These findings indicated that moderate levels of disturbance can optimize light utilization efficiency via an enhancement of water mixing and promote plant growth. In addition, two-way ANOVA revealed the significant interactive effects of water levels and disturbance on biological oxygen demand and total nitrogen concentration (p<0.05). On the basis of these findings, we propose an optimal regulation strategy of “high water levels (≥80 cm) combined with short-term disturbance (≤4 h)”, providing a theoretical basis for the synergistic restoration of submerged vegetation and improvements in aquatic environments within urban landscapes. These findings have practical significance for maintaining ecosystem stability in shallow lakes.
Constructed wetlands (CWs) are commonly used as the final treatment stage before discharging effluents from wastewater treatment plants (WWTPs) into natural waters. However, effectively treating carbon-limited but nutrient-enriched effluents remains challenging. Iron-rich substrates offer a promising solution because of their high adsorption capacities, redox activity, and biological affinity. In this study, we review the research directions and hotspots related to the application of iron-rich substrates in CWs, with an emphasis on their performance under low C/N ratio wastewater conditions. We also elucidate the synergistic mechanisms by which iron-rich substrates (i) stimulate microbial coupling of iron and nitrogen cycles for nitrogen removal and (ii) integrate surface adsorption, precipitation, ligand exchange, and co-precipitation for phosphorus removal. Considering the potential issues that may arise during the long-term operation of iron-rich CWs, such as iron passivation, clogging, microbial iron toxicity, and accumulation of denitrification byproducts, this study proposes recommendations for future research in terms of material development, system optimization, and mechanism exploration. These suggestions aim to provide strong support for improving purification efficiency and ensuring the long-term stable operation of CWs treating effluents from WWTPs.
To investigate the molluscicidal activity, hepatotoxic effects, and environmental toxicity of extracts from Asclepias curassavica, Phytolacca americana, and Cicuta virosa against Pomacea canaliculata, the present study systematically evaluated their effects at varying concentrations and exposure times based on an immersion method. Key hepatic physiological indicators and residual toxicity in water were also measured. All three plant extracts exhibited dose- and time-dependent molluscicidal effects. A. curassavica demonstrated the highest toxicity (48 h LC50=0.270 mL/L), being 3.03 times and 3.97 times more potent than P. americana (0.819 mL/L) and C. virosa (1.071 mL/L), respectively. Physiological indicators in the hepatopancreas indicated that toxic damage induced by A. curassavica and C. virosa was the most pronounced. This was reflected by a decrease in the levels of biomarkers associated with organismal damage, such as total protein (TP), malondialdehyde (MDA), and catalase (CAT), alongside an increase in activities of enzymes closely related to hepatic detoxification function, including acetylcholinesterase (AChE), glutathione S-transferase (GST), and alanine aminotransferase (ALT). Residual aquatic toxicity results demonstrated that A. curassavica caused the highest inhibition rate in luminescent bacteria (75% at LC75), whereas P. americana posed the lowest ecological risk (56% inhibition rate). Compared to traditional chemical molluscicides, the A. curassavica and P. americana extracts exhibit higher ecological safety, rendering them more suitable for eco-friendly control applications and demonstrating significant potential for development as botanical molluscicides.
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