Water pollution caused by various eutrophic nutrients such as nitrogen (N) and phosphorus (P), such as outbreaks of eutrophication in rivers and lakes, has become a serious environmental problem in China. Such problems have spurred extensive studies aiming at finding environmentally friendly solutions. Various constructed wetlands (CWs), planted with different macrophytes, have been considered as environmentally safe technologies to treat various wastewaters for several decades. Due to their low energy and operational requirements, CWs are promising alternative solutions to water eutrophication problems. Within the CWs, macrophytes, sediments, and the microbial community are indispensable constituents of such an ecosystem. In this study, a laboratory-scale surface flow CW (LSCW) was constructed to investigate the effects of two different plants, Eichhornia (E.) crassipes (Mart.) Solms and Myriophyllum (M.) aquaticum, on the removal of eutrophic N and P. The results showed that both plants could significantly reduce these nutrients, especially ammonium (NH₄⁺), and LSCW planted with M. aquaticum performed better (82.1% NH₄⁺ removal) than that with E. crassipes (66.4% NH₄⁺ removal). A Monod model with a plug flow pattern was used to simulate the relationship of influent and effluent concentrations with the kinetic parameters of this LSCW. Based on the model, a pilot-scale surface flow CW (PSCW) was designed, aiming to further enhance N and P removal. The treatment with M. aquaticum and polyethylene materials showed the best removal efficiency on NH₄⁺ as well as on total nitrogen and phosphorus. In general, the enlarged PSCW can be a promising solution to the eutrophication problems occurring in aquatic environments.

Massively input and accumulated ammonium is one of the main causes of eutrophication in aquatic ecosystems, which severely deteriorates water quality. Previous studies showed that one of the commonly used macrophytes, Myriophyllum aquaticum, was capable of not only withstanding ammonium of high concentration, but also efficiently assimilating extracellular ammonium to constitutive amino acids and proteins. However, the genetic mechanism regulating such efficient nitrogen metabolism in M. aquaticum is still poorly understood. Therefore, RNA-based analysis was performed in this study to understand the ammonium regulatory mechanism in M. aquaticum in response to various concentrations of ammonium. A total of 7721 genes were differentially expressed, of which those related to nitrogen-transport, assimilation, and remobilization were highly-regulated in response to various concentrations of ammonium. We have also identified transcription factors and protein kinases that were rapidly induced in response to ammonium, which suggests their involvement in ammonium-mediated signalling. Meanwhile, secondary metabolism including phenolics and anthocyanins biosynthesis was also activated in response to various concentrations of ammonium, especially at high ammonium concentrations. These results proposed a complex physiological and genetic regulation network related to nitrogen, carbohydrate, transcription factors, and secondary metabolism for nitrogen use efficiency in M. aquaticum.