Constructed wetlands are an integral part of stormwater management and onsite sewage treatment solutions for green building projects. When there is enough land available, such as in suburban office park developments, these systems function both to hold stormwater and to use treated sewage to supply nutrients to aquatic plants and animals. As most ecology stu­dents learn, wetlands are the most productive ecosystems in the world, straddling the intersection of land and water. They are also nature’s filters, helping to remove sediments and heavy metals, as well as oil and grease, from stormwater and transforming sewage nutrients into life­-giving car­bon, nitrogen, phosphorus and trace minerals. Properly designed, con­structed wetlands can provide wildlife habitat and open space for green building projects, as well as a place for school tours and outdoor environ­mental education.

Schematic design of constructed wetlands for sewage treatment. (Image courtesy of Natural Systems International)

Constructed wetlands can have either surface or subsurface flows. Surface flows resemble marshes, while subsurface flows support a wide va­riety of plants by supplying them with nutrients. Plantings of reed beds are popular in European constructed wetlands, and plants such as cattails, sedges and bulrushes are used worldwide.  As of 2004 more than 5,000 constructed wetlands had been built in Europe, and more than 1,000 were in operation in the U.S.

Constructed wetlands may be cheaper to build than traditional sewage and stormwater treatment plants, have lower operating and main­tenance costs and be able to handle widely varying volumes of wastewater. For example, the Tres Rios constructed wetlands is a 7­-mile, 480-­acre riparian corridor in the southwestern part of Phoenix, at the conjunction of the Salt and Gila rivers. As a wildlife sanctuary and place of repose in an in­creasingly dense urban area, Tres Rios not only treats sewage from the 91st Avenue treatment plant, but also provides many public­-use benefits for the Phoenix metropolitan area.