Constructed wetlands are engineered stormwater management systems designed to mimic the structure and function of natural wetlands in order to treat, store, and manage stormwater runoff through a combination of physical, chemical, and biological processes. They are intentionally designed and built to improve water quality, reduce runoff volumes, and provide ancillary ecological benefits.
Constructed wetlands consist of shallow basins that are either permanently or intermittently inundated with water and are planted with wetland vegetation adapted to saturated soil conditions. These systems typically include distinct zones, such as forebays for initial sediment capture, shallow marsh areas with emergent vegetation, and deeper pools that promote settling and biological activity. Water flows slowly through the system, allowing time for treatment processes to occur.
From a treatment perspective, constructed wetlands remove pollutants through several mechanisms. Sedimentation allows suspended solids to settle out of the water column. Filtration occurs as water passes through dense vegetation and organic soils. Chemical processes, such as adsorption and precipitation, help remove nutrients and metals. Biological uptake by plants and microbial communities further reduces concentrations of nutrients, particularly nitrogen and phosphorus, which are associated with issues like eutrophication.
Hydrologically, constructed wetlands provide temporary storage of stormwater, attenuating peak flows and reducing downstream erosion potential. They also promote some infiltration and evapotranspiration, contributing to overall water balance within a watershed.
In addition to water quality and quantity benefits, constructed wetlands can provide habitat for wildlife, enhance site aesthetics, and support biodiversity. However, they require careful design, including appropriate sizing, hydraulic residence time, vegetation selection, and maintenance considerations, to function effectively.
Constructed wetlands are widely used in both urban and rural settings as part of integrated stormwater management strategies, particularly where space is available and long-term, naturalized treatment systems are desired.