Nutrient Remediation by Canna flaccida and Juncus effusus In Floating Treatment Wetlands

Floating treatment wetlands (FTWs) are an emerging technology for cleansing nutrient rich stormwater and agricultural runoff.  The goal of this research was to characterize the influence of individual plant species on nutrient removal dynamics in FTWs.  To accomplish this goal, we evaluated how percent cover, planting density, and aeration influenced nutrient remediation by soft rush (Juncus effusus) and golden canna (Canna flaccida) established in FTWs using a replicated mesocosm study.  Influent nitrogen (N = NO₂-N + NO₃-N + NH₃⁺-N) concentrations averaged 19.2 ± 1.98 mg^.l^-1 for rush and 20.9 ± 1.84 mg^.l^-1 for canna, and influent phosphorus (P= inorganic + organic P fractions) concentrations averaged 3.52 ± 0.28 mg^.l^-1 for rush and 4.44 ± 0.34 mg^.l^-1 for canna.  Plant growth parameters were measured on a biweekly basis, and water quality parameters were monitored on a weekly basis.  At each experiments conclusion, fresh weight was recorded for all plant tissue in each experimental unit.  Three plants per experimental unit were weighed (fresh and dry) and tissues analyzed for mineral composition.  Aeration enhanced root growth of both plant species but did not consistently enhance shoot growth.  The highest nutrient uptake into tissue for canna (160.8 ± 11.3 g^.m^-2 N, 26.4 ± 1.93 g^.m^-2 P) and rush (138.1 ± 8.45 g^.m^-2 N, 26.3 ± 1.72 g^.m^-2 P) were reported in the 50% cover treatments.  Canna aided nitrogen removal was greater than that of rush.  Canna and rush non-aerated treatment effluent N concentrations averaged 5.25 ± 1.56 mg^.l^-1 and 13.4 ± 1.27 mg^.l^-1, respectively, while aerated treatment effluent N concentrations for canna were 8.59 ± 1.60 mg^.l^-1 and for rush 16.3  ± 1.93 mg^.l^-1.  Canna and rush phosphorus removal were similar.  Non-aerated treatment P effluent concentrations averaged 2.08 ± 0.32 mg^.l^-1 while aerated effluent concentrations averaged 2.36 ± 0.35 mg^.l^-1.  Non-aerated floating wetlands better facilitated both N and P removal in these experiments.  Canna reduced effluent nitrogen concentrations more efficiently than rush.  Our future studies will evaluate the influence of mixed species on nutrient uptake as mixed culture systems may more effectively remediate contaminants.