Rewetting in Mediterranean reclaimed peaty soils and its potential for phyto-treatment use

A pilot experimental field combining rewetting of reclaimed peaty soils and water phyto-treatment was set up in the Massaciuccoli Lake basin (Tuscany, Italy) to reduce the water eutrophication and peat degradation caused by almost a century of drainage-based agricultural use. In this paper, we investigated the restoration process occurring consequently to the conversion of a drained area in a natural wetland system (NWS) (the partial top soil removal, the realization of a perimeter levee to contain the waters, the rewetting with the drainage waters coming from the of surrounding cultivated areas) and the capability of the spontaneous vegetation to catch nutrients acting as a vegetation filter. To follow the restoration process over time (2012-2016), we used a mixed approach merging phytosociological surveys with ortophotos taken by an Unmanned Aerial Vehicle (UAV). During the last year of observation (2016), we performed destructive sampling on the most widespread plant communities in the area (Phragmites australis and Myriophyllum aquaticum community) to quantify the biomass production and the uptake of nitrogen and phosphorus. Stands of Phragmites australis (Cav.) Trin. ex Steud. yielded more than Myriophyllum aquaticum (Vell.) Verdc. (4.94 kg m-2 vs 1.08 kg m-2). M. aquaticum showed higher nutrient contents (2.04% of N and 0.35% of P), however P. australis was able to take up more nutrients within the NWS because of its larger cover and productivity. In the perspective of maximizing the plant development and consequently the amount of nutrients extracted from treated waters, the authors suggest 4-5 year-long-harvesting turns, better occurring in spring-summer.