Assessing the water purification service in an integrated agricultural wetland within the Venice lagoon drainage system

Wetlands are a cornerstone of beneficial ecosystem services, especially in intensive agricultural landscapes characterised by nutrient loss, and shallow and surface water bodies. Water-purification services can trap 80–90% of the sediments and eliminate 70–90% of the entering nitrogen. An experimental wetland of 3.2 ha was created within the Venetian drainage system to control nutrient loss from croplands and protect surface water bodies. The aims of the present study were to assess the water-purification service by monitoring nutrient runoff and testing the adaptability of seven macrophyte species in a floating treatment wetland system. Results showed that median concentrations of total nitrogen were 2.43 ppm at the inlet and 1.79 ppm at the outlet, whereas after an extreme rainfall event, total nitrogen concentrations were 6.34 ppm at the inlet and 1.29 ppm at the outlet. Carex spp. adapted best to the floating wetlands (433.13 g m–2 of biomass production), followed by Lythrum salicaria (210.32 g m–2). Carex spp. had the highest total nitrogen uptake (4.84 g m–2), mostly in roots (3.19 g m–2), followed by L. salicaria with 2.35 g m–2. Constructed wetlands could, therefore, play a crucial role in integrated agro-environmental management to control nutrient runoff from intensive cropping systems.