Functions of Macrophytes in Constructed Wetlands

TLDR

Macrophytes possess intrinsic properties that make them indispensable in constructed wetlands, offering habitat for wildlife, aesthetic appeal, and bed stabilization. The study investigates the physical effects of macrophytes on wastewater treatment in constructed wetlands. Macrophytes stabilize beds, enhance physical filtration, prevent clogging, insulate against frost, provide extensive surface area for microbial growth, do not raise hydraulic conductivity, influence treatment processes depending on wetland design, contribute quantitatively to nutrient uptake only in low‑loaded surface flow systems, and transfer oxygen to the rhizosphere, boosting aerobic degradation and nitrification.

Abstract

Macrophytes have several intrinsic properties that makes them an indispensable component of constructed wetlands. The most important functions of the macrophytes in relation to the treatment of wastewater are the physical effects brought about by the presence of the plants. The macrophytes stabilise the surface of the beds, provide good conditions for physical filtration, prevent vertical flow systems from clogging, insulate against frost during winter, and provide a huge surface area for attached microbial growth. Contrary to earlier belief, the growth of macrophytes does not increase the hydraulic conductivity of the substrate in soil-based subsurface flow constructed wetlands. The metabolism of the macrophytes affects the treatment processes to different extents depending on the design of the constructed wetland. Plant uptake of nutrients is only of quantitative importance in low-loaded systems (surface flow systems). Macrophyte-mediated transfer of oxygen to the rhizosphere by leakage from roots increases aerobic degradation of organic matter and nitrification. The macrophytes have additional site-specific values by providing habitat for wildlife and making wastewater treatment systems aesthetically pleasing.