Green Infrastructure benefits of constructed wetlands
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Stormwater wetlands are similar in design to stormwater ponds and mainly differ by their variety of water depths and associated vegetative complex. They require slightly more surface area than stormwater ponds for the same contributing drainage area. Stormwater wetlands are constructed stormwater management practices, not natural wetlands. Like ponds, they can contain a permanent pool and temporary storage for water quality control and runoff quantity control.
Green Infrastructure benefits of constructed wetlands
| Benefit | Effectiveness | Notes |
|---|---|---|
| Water quality | Primary benefit is retention of sediment; may export phosphorus if not designed and maintained properly. | |
| Water quantity/supply | Rate control benefit. | |
| Energy savings | ||
| Climate resiliency | Provides some rate control. Impacts on carbon sequestration are uncertain. | |
| Air quality | ||
| Habitat improvement | Use of perennial vegetation and certain media mixes promote invertebrate communities. | |
| Community livability | Aesthetically pleasing and can be incorporated into a wide range of land use settings. | |
| Health benefits | ||
| Economic savings | Generally provide cost savings vs. conventional practices over the life of the practice. | |
| Macroscale benefits | Individual practices are typically microscale, but multiple practices, when incorporated into a landscape design, provide macroscale benefits such as wildlife corridors. | |
| Level of benefit: ◯ - none; ◔ - small; ◑ - moderate; ◕ - large; ● - very high | ||
- Water quality: Bioretention is an excellent stormwater treatment practice due to the variety of pollutant removal mechanisms, including vegetative filtering, settling, evaporation, infiltration, transpiration, biological and microbiological uptake, and soil adsorption. Bioretention can be designed as an effective infiltration / recharge practice, particularly when parent soils have high permeability (> ~ 0.5 inches per hour). Bioretention designed for infiltration (bioinfiltration) removes 100 percent of pollutants for the portion of runoff water that is infiltrated, although there may be impacts to shallow groundwater. Bioretention designed as filtration (biofiltration) employs engineered media that is effective at removing solids, most metals, and most organic chemicals. Removal of phosphorus depends on the media (link here). Links to water quality information for bioretention - [1]; [2]
- Water quantity and hydrology: Bioretention can be designed as an effective infiltration / recharge practice when parent soils have high permeability. For lower permeability soils an underdrain is typically used and some infiltration and rate control can be achieved.
- Climate resiliency: It is unclear if bioretention provides benefits for climate resiliency. Carbon may be sequestered, particularly if shrubs and trees exist in the practice. Bioretention also provides some reduction in peak flow. Carbon emissions for construction and maintenance may offset carbon benefits (Moore and Hunt, 2013). Winston (2016) provides a detailed analysis of resiliency of bioretention systems based on different design considerations, such as bowl depth and vegetation utilized in the practice. A complex of wetland types interspersed with upland nesting cover provides optimum habitat but is difficult to achieve in most urban environments ([3];).
- Habitat improvement: Constructed wetlands, designed to retain a permanent pool, provide excellent wildlife habitat. Many wildlife species are dependent on or otherwise utilize wetland habitats, including waterfowl, wading birds, shorebirds and songbirds, furbearers such as beaver, muskrat and mink, and a variety of reptiles and amphibians like turtles, snakes, frogs, salamanders, and toads. An important factor affecting the habitat value of a constructed wetland is the surrounding landscape.
- Community livability: Bioretention is an aesthetically pleasing practice that can easily be incorporated into various landscapes. A variety of vegetation can also be used, including perennial plants, shrubs, and trees.
- Health benefits: Green spaces may also improve mental and physical health for residents and reduce crime (Barton and Rogerson, 2017).
- Economic savings: Properly designed and integrated bioretention practices provide life cycle cost savings. Well designed and maintained bioretention practices increase property values.