Evaluating functions and benefits of constructed wetlands

The use of constructed wetlands for treatment of wastewater has steadily increased in the last decades. Besides the direct benefits of water purification, these systems are also associated with high ancillary benefits deriving from the creation of a natural habitat that is aesthetically pleasant, supports local wildlife and is suitable for recreational and cultural activities. This paper aims at identifying the wide range of benefits associated with constructed wetlands. For this purpose we embrace an analysis anchored on an economic perspective on constructed wetlands values. The resulting framework is the starting point for discussing the possibility of estimating these values in monetary terms. Suggestions are made about which economic valuation method can address which type of constructed wetland value. The possibility of using benefit transfer from studies concerning natural wetlands is also discussed. The results of such an economic valuation exercise reveal to be crucial for cost-benefit analysis and for public policy guidance. 1. An introduction to constructed wetlands The recognition of the existence of water purification processes within wetland systems has led in the last decades to the development of new strategies of wastewater treatment that include the creation of artificial wetlands. In one of the most widely accepted definitions, constructed wetlands are “man-made complexes of saturated substrate, emergent and submerged vegetation, animal life and water that simulate natural wetlands for human use and benefits” (Hammer and Bastian, 1989). The application of constructed wetlands for treatment of municipal wastewater is constantly increasing due to good treatment performances and low construction and operating costs (Kadlec et al. 2000). As polishing step of conventionally engineered wastewater treatment plants, constructed wetlands seem to represent an effective, technologically simple and economically affordable solution to the increasing pressure on surface waters. As a linkage-system between municipal wastewater treatment plant and (re)use of treated wastewater, they also represent a sustainable ecotechnological application of integrated water management that can significantly contribute to compliance with the European Water Framework Directive (EU 2000/60). Their high quality effluents can be suitable for reuse in various forms. Constructed wetlands for wastewater treatment are generally classified on the basis of the wastewater flow type into the categories of (i) free water surface and (ii) subsurface flow systems.