Excessive use of commercial fertilizers in nursery production results in substantial fertilizer runoff, leading to surface and groundwater contamination. Therefore, to prevent contamination and comply with regulations, irrigation return flow (runoff water) is generally collected in a retention pond before it can be safely discarded or released. Nitrogen, applied as nitrate compounds is among the highest used fertilizer and is prone to leaching and runoff. Employing a phytoremediation strategy to remediate irrigation return flow (runoff water) has the potential to lower nitrate concentrations in water before release. In this study, we assessed the suitability of growing Helianthus maximiliani (maximilian sunflower) and Asclepias speciosa (showy milkweed) in a floating treatment wetland system (FTW) and evaluated the nitrate uptake capacity of these plants grown in three different nitrogen concentrations i.e., 10, 20, and 30 mg/L and two water temperatures of 75°F and 85°F. Increasing water temperature increased growth index for both species and increased dry weight for Asclepias speciosa. However, for Helianthus maximiliani, increasing temperature had a lesser effect on total dry weight. The accumulation of nitrate nitrogen in plant tissue was higher in Helianthus maximiliani at the nitrate nitrogen concentration of 20 mg/L under both temperature treatments. However, in Asclepias speciosa, the accumulation of nitrate nitrogen in plant tissue was higher at the high temperature treatment of 85⁰F and 20 mg/L nitrate nitrogen concentration. The nitrate nitrogen uptake from both plants in this study indicated suggests that Helianthus maximiliani ‘maximilian sunflower’ and Asclepias speciosa ‘showy milkweed’ can be grown as FTW and be used to remove nitrogen from a nursery retention pond.
