Plants and Phytoremediation
Unlike raingardens, wet ponds are designed to capture and hold runoff from impervious cover. Urban runoff can carry pollutants such as gasoline, motor oil, heavy metals, fertilizers, pesticides, aromatic hydrocarbons (PAHs), nickel, copper, zinc, cadmium, lead, synthetic organic compounds, zinc nitrates and phosphorus. Phytoremediation is the use of plants for cleaning up contaminants in soil, groundwater, surface water and air. Fortunately, the plant communities ESC establishes and manages in regional wet ponds are phytoremediation rock stars!
Pontederia cordata (pickerelweed), shown at left, Thalia dealbata (alligator flag), and Canna glauca (golden canna) remove excess nitrogen and phosphorus from standing water. Their beautiful flowers enhance the aesthetic value of wet ponds. Sagittaria (arrowhead) binds cadmium and zinc to its roots, accumulates heavy metals and may even remediate diesel. Eleocharis (spikerush) and Equisetum (horsetail) are lead hyperaccumulators. Schoenoplectus (bulrush) uptakes zinc and Justicia (water willow) uptakes iron. These plants break down or degrade pollutants by acting as filters to improve the quality of water entering our streams and lakes.
Salix nigra (black willow) often volunteers in riparian zones. Salix phytoremediates copper, zinc and lead.
Willows also facilitate denitrification (a microbially facilitated process where nitrate is reduced to nitrogen) and provide a more hospitable soil condition for native plant species which are not able to tolerate high soil nitate levels. Helianthus annuus (annual sunflower), shown at right, was used in Chernobyl, Ukraine to remove radioactive contaminants from groundwater.
To explore further, here’s a phytoremediation website that offers species information searchable by common and scientific names http://www.steviefamulari.net/phytoremediation/index.php