Estimation of the performance of an experimental free water surface wetland in the Venice Lagoon watershed.

We established a pilot wetland to verify the efficiency of free water surface wetlands in improving the inlet surface water quality of Venice Lagoon. Three subsystems were recognized in the wetland: (i) riparian swamp, (ii) riparian-marsh transition zone, and (iii) marsh. We evaluated the abatement efficiency over three experimental years (2002–2005). The effect of detention times of 14 and 7 days was also tested. There was good nitrogen removal (58% of total nitrogen and 85% of N-NO3 with 14-d detention time), especially in the first subsystem, and variable phosphorus removal (44% of total phosphorus with 14-d detention time), located mostly in the second subsystem. The whole three-subsystem mosaic performed better than each part alone. We calibrated a first-order areal model of nitrogen to estimate local parameters for future planning of treatment wetlands in the Venice Lagoon watershed. To calibrate the model different methods and data sets were used. The calibration of removal rate constants using different approaches led to comparable results; however, the transect data approach provided additional information on wetland performance.