Because natural wetlands are so effective at removing pollutants from water that flows through them, engineers and scientists construct systems that replicate some of the functions of natural wetlands. These constructed treatment wetlands use natural processes involving wetland vegetation, soils and their associated microbial life to improve water quality. They are often less expensive to build than traditional waste-water and storm-water treatment options, have low operating and maintenance expenses and can handle fluctuating water levels. For example, in 1990 city managers in Phoenix, Arizona, needed to improve the performance of a waste-water treatment plant to meet new state water quality standards. After learning that upgrading the plant might cost as much as $635 million, the managers started to look for a more cost-effective way to provide final treatment to the plant's waste-water discharge into the Salt River. A preliminary study suggested that a constructed wetland system would sufficiently clean the discharged water while supporting high-quality wetland habitat for birds, including endangered species, and protecting downstream residents from flooding. All these benefits would be achieved at a lower cost than retrofitting the existing treatment plant. As a result, the 12-acre Tres Rios Demonstration Project began in 1993 with assistance from the Corps of Engineers, the Bureau of Reclamation and EPA's Environmental Technology Initiative and now receives about two million gallons of waste-water per day. This project is still flourishing, serving as a home for thousands of birds and other wildlife. There are hundreds of waste-water treatment wetlands operating in United States today.
"To halt the decline of an ecosystem, it is necessary to think like an ecosystem."