Multi-pollutant removal dynamics by aquatic plants in monoculture or mixed communities

Much of our knowledge about the phytoremediation potential of floating treatment wetlands (FTWs) comes from studies focusing on the removal of single pollutants, often by a single plant species. Here, we quantify the potential of FTWs planted with varying proportions of the emergent monocots Typha latifolia, Glyceria maxima, and Phragmites australis to simultaneously remove a suite of eleven nutrient/metalloid pollutants. Pollutants most readily removed from water included total inorganic nitrogen (TIN), K and Mn, whilst P, Zn and Cu showed a moderate removal efficiency, and Mg, Ca, Na, Cr, and Fe were poorly removed. Root length within a FTW was correlated with lower concentrations of Ca, Mg, K, P, and Zn remaining in the water, whilst plant uptake and tissue sequestration was more important for reducing concentrations of Mn, TIN, P, and Fe. The effect of community composition over time was greatest for the removal of Zn, with FTWs containing T. latifolia having the strongest effect; community type was less important for the removal of TIN, Mg, K, and Na. Plant tissue sequestration was important for reducing concentrations of Mn, TIN, P and Fe in the water, with median uptake values all greater than 12.5%. Importantly, the removal of some pollutants (e.g., Cu) increased with retention time. Therefore, depending on the management objective, FTWs generally perform better where and when residence times are longer e.g., in ponds or streams under low flow, and assembling FTW communities with varying traits and associated removal mechanisms can allow several pollutants to be remediated at once.