RENINGSEFFEKT MOT KOSTNADSEFFEKTIVITET I ANLAGDA VÅTMARKER / Retention capacity versus cost efficiency in constructed wetlands
A large number of wetlands have been created in the northwest part of Scania (south of Sweden) since 1991. Their types of construction vary, which affect their ability to remove nutrients from eutrophic watercourses. In this report, we have evaluated how different construction techniques affect nitrogen retention capacities and
compared cost-efficiencies between different wetlands. The wetlands were constructed during two different periods (1991–1998 and 1999–2002), which had different background conditions. The best projects were generated during the most recent period. The improvements made can be summed up as bigger and more cost efficient wetlands, with better water flow patterns and with more efficient nitrogen retention capacities, given a specific load. The evaluation also shows that economic policies rendered positive effects in more than one way. They supplied resources for wetland constructions and they also generated wetland projects with high cost efficiencies. This is due to the fact that the resources were limited and therefore were used more efficiently. In other words, we are starting to find optimal ways of establishing wetlands. Wetlands should be loaded with nitrogen in concentrations of 2–50 tonnes nitrogen per hectare and annum, they should not be constructed as shafts but as dams and/or as altered watercourses, and they should have horizontal flows.