No abstract

The chemical oxygen demand (COD) is selected as the index in this paper. The system dynamics method is used to analyze the emission right price of medical sewage, the boundary of the emission right price system is determined, and the system dynamics model of the initial emission right of medical sewage is constructed, in which the system is divided into water resources subsystem, population subsystem, economic subsystem and social subsystem. It is expected to expand the theory of the system modeling of the initial discharge right of medical sewage, and to provide the basis for the relevant decision of the environmental management authorities.

Cadmium (Cd) is highly toxic and widely distributed in aquatic systems due to its high solubility and mobility in water, which can severely inhibit the survival of aquatic macrophytes. The phytotoxicity of Cd depends on environmental factors; however, it remains unclear whether and how light quality affects its toxicity on aquatic macrophytes. In this study, we investigated the effects of Cd on aquatic macrophytes Potamogeton crispus under different light qualities (white, blue, and red light). We evaluated morphological and photo-physiological traits, as well as the cellular antioxidant defense system. Our findings indicate that P. crispus under Cd stress showed notable damage in leaf morphology, decreased photosynthetic efficiency, inhibited HCO3− uptake, and reduced antioxidant enzyme activities, as well as oxidative damage indicated by MDA accumulation and superoxide (O2−) overproduction. However, compared with white or red light under Cd stress, blue light reduced structural damage and oxidative stress caused by Cd while increasing pigment synthesis and photosynthetic efficiency, as well as increasing ascorbate peroxidase (APX) activity. In conclusion, the changes induced by blue light in P. crispus’s photosynthesis and antioxidant system strengthen its tolerance to Cd. Further research on signal transmission in relation to light quality in Cd-exposed aquatic plants is still needed.