Quick answers to frequently asked questions about constructed wetlands.

What is a constructed wetland? Constructed wetlands are a technology designed to mimic processes found in natural wetland ecosystems.  These systems utilize wetland plants, soils and their associated microorganisms to remove contaminants from wastewater, as well as other sources. As with other natural biological treatment technologies, wetlands treatment systems are capable of providing additional benefits. The reuse, or reclamation, of wastewater using constructed wetland technology also provides an opportunity to create or restore valuable wetland habitat for wildlife and environmental enhancement.

How does constructed wetland technology work? Constructed wetlands technology can improve water quality through a variety of biological processes that naturally occur in wetland environments.  In short, microorganisms that live on aquatic plants and in soils transform organic matter and nutrients present in wastewater effluent into types of nutrients that support a diverse community of aquatic pond life.  Plants also play an active role in taking up available nitrogen, phosphorous, and other nutrients from wastewater.

Are there many constructed wetlands currently in operation? Currently over 500 wastewater and stormwater treatment wetlands have been constructed in the US alone.  This technology is widely accepted and it is increasingly being used.  Their application ranges from small rural communities, such as Mt. Angel, Oregon, to large urban areas, such as Phoenix, Arizona.

What is the difference between treatment and enhancement wetlands? A treatment wetland is generally designed to treat municipal or industrial effluents, as well as stormwater runoff.  An enhancement marsh is designed to benefit the community in other ways.  Enhancement wetlands are systems with multiple uses such as water reclamation, wildlife habitat, water storage, mitigation banks, and may also provide passive recreational and environmental education opportunities.  Both of these types of wetland systems can be designed separately, or important attributes of each can be integrated into a single design with multiple treatment and enhancement objectives.

Is the use of constructed wetlands limited by location or climate? This technology can be applied in a wide range of geographic areas including arid, tropical, and alpine regions, and can even treat nutrient rich effluents in extreme weather conditions (i.e. freezing).  Constructed wetlands projects can range widely in size, shape, and location, with a major constraint being the amount of land required.

Are constructed wetlands reliable? What do they treat? When applied appropriately and constructed properly, treatment wetlands can effectively remove most pollutants associated with municipal and industrial wastewater and stormwater.  Treatment wetlands are especially efficient at removing contaminants such as BOD (biochemical oxygen demand), suspended solids, nitrogen, phosphorus, hydrocarbons and even metals.  Constructed wetlands are an effective and reliable water reclamation technology if they are maintained and operated properly.

What are some of the maintenance issues associated with wetland treatment technology? Maintenance associated with treatment wetlands is generally limited to the control of unwanted aquatic plants and control of vectors, such as mosquitoes.  Effective vector control can be achieved by appropriately applying integrated pest management practices such as introducing mosquito fish or providing swallow habitat.  The accumulation of sediment is not generally a problem in a well designed and operated constructed wetland; thus dredging is rarely if ever required.