Abstract
Surface flow constructed wetlands (SFCWs) can be effectively used to treat agricultural drainage waters, reducing N and P surface water pollution. In the Venice Lagoon drainage basin (northeastern Italy), an SFCW was monitored during 2007–2013 to assess its performance in reducing water, N, and P loads more than 10 years after its creation. Nitrogen concentrations showed peaks during winter due to intense leaching from surrounding fields. Phosphorus concentrations were higher after prolonged periods with no discharge, likely due to mobilization of P of the decomposing litter inside the basin. Over the entire period, N removal efficiency was 83% for NO3–N and 79% for total N; P removal efficiency was 48% for PO4–P and 67% for total P. Values were higher than in several other studies, likely due to the fluctuating hydroperiod that produced discontinuous and reduced outflows. Nitrogen outlet concentrations were reduced by the SFCW, and N removal ratios decreased with increasing hydraulic loading, while no strong correlations were found in the case of P. The SFCW was shown to be an effective long-term strategy to increase water storage and reduce N and P loads in the Venice Lagoon drainage basin.
Highlights
Surface flow constructed wetlands (SFCWs) are nature-based solutions, created to mimic natural systems [1], where plants grow partly submerged in water, with the roots in the soil
Nitrogen outlet concentrations were reduced by the SFCW, and N removal ratios decreased with increasing hydraulic loading, while no strong correlations were found in the case of P
After 17 years of operation, the SFCW was still effective in reducing NO3 –N, total N, PO4 –P, and total P loads coming from agricultural drainage waters
Summary
Surface flow constructed wetlands (SFCWs) are nature-based solutions, created to mimic natural systems [1], where plants (usually macrophytes) grow partly submerged in water, with the roots in the soil. SFCWs are considered cost-effective in reducing nonpoint-source pollution, especially when treating agricultural surface waters that are rich in nutrients [4,5,6], especially nitrogen (N) and phosphorus (P) [7]. They perform well in reducing nitrogen loads through nitrification-denitrification processes and plant uptake [8,9,10], whereas phosphorus removal largely depends on a combination of sedimentation, adsorption-desorption, complexation, and precipitation phenomena [6,11]. Fisher and Acreman [14], reviewing the performances of N and P removal of riparian, floodplain, and marsh wetlands in Agronomy 2019, 9, 170; doi:10.3390/agronomy9040170 www.mdpi.com/journal/agronomy
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