2018 ASHS Annual Conference

Floating treatment wetlands (FTWs) are a constructed wetland technology that directly exposes roots of plants to the water column. This exposure of water to the root system leads to an increase in nutrient uptake and remediation and a possible decrease in plant pathogen loading. Research at Clemson University was conducted between 2015 and 2018 to assess a variety of plant species for both their nutrient remediation efficacy, specifically nitrogen (N) and phosphorus (P), as well as their susceptibility to Phytophthora spp. Five species of plants were trialed for nutrient remediation and pathogen susceptibility (Iris ensata, Pontederia cordata, Agrostis alba, Carex stricta, and Panicum virgatum). An additional three species were assessed for nutrient remediation only (Andropogon glomeratus, Canna ‘Firebird’, and Juncus effusus) and an additional two species were assessed for pathogen susceptibility only (Sagittaria latifolia and Typha latifolia). Plants for nutrient remediation analyses were suspended using a floating mat and aerator cups in a mesocosm study, while plants for pathogen susceptibility analyses were floated in 2.5 L pots. Plants were exposed to either elevated levels of nutrients (5 ppm N or 12 ppm N) or one of five species of Phytophthora (P. citrophthora, P. cinnamomi, P. cryptogea, P. nicotianae, P. palmivora) in a 10 ppm N nutrient solution. While C. ‘Firebird’, A. alba, and P. cordata removed greater than 50% of nitrate from the system, maximum phosphorus removal was 28% and 12% with P. virgatum and C. ‘Firebird’, respectively. While there were no detected root infections by Phytophthora spp. during the 2016 pathogen trial, roots of C. stricta, P. virgatum, and T. latifolia were found to be infected in the 2017 trial. Both I. ensata and P. cordata show promise for FTW installations in nursery and greenhouse applications due to their nutrient remediation capabilities and apparent pathogen resistance. Further testing is needed to determine pathogen remediation efficacy of the trialed plants, as well as nutrient remediation efficacy and plant pathogen susceptibility of other aquatic plant species.