A 2014 study found that tanks with floating wetlands populated with Iris pseudacorus removed 54 times more nitrogen and 10 times more phosphorus from the water than a control tank with no vegetation.
Keizer-Vlek, Hanneke E., Piet FM Verdonschot, Ralf CM Verdonschot, and Dorine Dekkers. (2014). The contribution of plant uptake to nutrient removal by floating treatment wetlands. Ecological Engineering, 73, 684-690.