Wetland restoration is considered an effective mitigation method for decreasing nitrogen (N) losses from agricultural land. However, when former cropland becomes rewetted, there is a risk that phosphorus (P) accumulated in soils will be released downstream. Here, we evaluate N and P retention in eight restored wetlands in Denmark monitored for 1 year using a mass balance approach. The wetlands represented different types, for instance, lakes and wet meadows, and ages (3-13 years). We also show the results from a long-term monitoring station established in 1973, located downstream a lake that was re-established in 2006. All restored wetlands removed total N (42-305 kg N ha-1 year-1), while some wetlands acted as source of total P and others as a sink (- 2.8 to 10 kg P ha-1 year-1). Our study confirms that restored wetlands are effective at removing N, whereas P can be released for several years after restoration.
Keywords: Eutrophication; Hydraulic residence time; Nitrogen; Phosphorus; Wetland restoration.