Urban Trees Help Clean Our Stormwater

In urban environments many cities around the globe use biofiltration systems to capture and filter potentially contaminated water running off and causing pollution. The research on how soils and woody plants like trees filter water is not extensive and is lacking. The University of Melbourne tried to fill in this gap as much as possible with specifically designed experiment, detailed in an article by the American Society of Agronomy.

The experiment was based on four different trees commonly used as street trees in Australia; the soils were varied while some trees were not planted to serve as controls. They watered the trees with either a solution similar to stormwater or regular tap water. The stormwater solution contained high levels of nutrients such as nitrogen and phosphorus. These are typical in areas where you have fertilizer runoff contaminating stormwater runoff. These levels can quickly go from nutrient to contaminant and stimulate algal blooms creating toxicity in those water bodies. This can result in fish death, loss of biodiversity in the water and also dead zones.

This project spanned 13 months and measured how well the different tree species grew and took extra nutrients out of the stormwater. All four species receiving stormwater grew significantly larger than those receiving tap water, demonstrating all have potential to thrive under urban conditions. The results also indicated the trees are good at unpacking nutrients from stormwater. The unplanted soils on the other hand showed leaching of nutrients. It appeared that the species selection was not essential to maximize the nutrient removal performance of the biofiltration system.

Biodiversity and biofiltration is critical within our cities and we can all contribute to this by planting our own trees to be a part of that system. Each Tree In A Box kit has the potential to grow multiple trees and can create your own urban forest in your front yard, or even in potted plants on your apartment or condominium terrace.