2017 ASHS Annual Conference

Greenhouse and nursery effluent often contains elevated levels of nitrogen and phosphorus which can limit potential for recycling water on site for production or cause problems in the environment. Floating treatment wetlands (FTWs) are comprised of a buoyant mat planted with macrophytes that absorb and filter the excess nutrients. One of the leading problems with FTWs is the senescence point, when plants begin releasing nutrients back into the water column. A mesocosm study was conducted in the summer of 2016 to (1) determine efficacy of common landscape plants to remediate nutrients from water and (2) assess plant viability for container or bare root resale at harvest. An experimental system was assembled using 32 100-gallon Rubbermaid water troughs. The water troughs were filled with water spiked with 12 ppm nitrogen fertilizer. Plants were placed in biodegradable aerator cups and inserted into precut holes with the floating mats. Four troughs were treated as an open water control while the remaining 28 troughs were planted with either a monoculture or mixture of five plant species; Iris ensata (Japanese iris), Canna x generalis ‘Firebird’ (Firebird canna), Agrostis gigantean (redtop), Carex stricta (Tussock sedge), and Panicum hemitomon (Maidencane). Plants were grown for eight weeks to quantify nutrient remediation efficacy prior to harvest. At the end of the eight-week period, three plants from each monoculture were removed and transplanted into 11.4 L plastic pots, including the biodegradable cup. The pot was filled with soilless substrate and placed on a growing pad to determine post-harvest survival and aesthetics. An additional three plants from each monoculture were removed and direct planted into cecil sandy loam on a pond’s edge to mimic wetland restoration techniques. Survival and aesthetics were assessed for eight weeks, consisting of weekly observations based on a scale from 1-5. While C. ‘Firebird’ and A. alba removed greater than 50% of nitrate from the system, maximum phosphorus removal was 28% and 12% with P. virgatum and C. ‘Firebird’, respectively. Plants transplanted into pots outperformed those planted using wetland restoration techniques. C. ‘Firebird’, P. virgatum and A. alba maintained aesthetic standards with > 4.5 rating for resale during the eight-week period, while C. ‘Firebird’ and I. ensata performed best when planted pondside with an average 3.6 rating. Based upon current results, C. ‘Firebird’, P. virgatum and A. alba are viable options for use in FTWs to remediate nutrients followed by harvest and resale as a container crop.