Trees Tuesday: Water Quality

So we now know that trees can reduce air pollution and help us save energy, but they don't stop there. Trees improve the quality of our water as well.

In the city, most of the ground is covered in hard surfaces like buildings, concrete, asphalt, etc. Water cannot penetrate these surfaces easily, so it flows over them instead until it reaches storm sewers and drainage pipes. As water runs over these surfaces, it erodes what little soil is exposed, and picks up dirt and pollutants, such as nitrogen, phosphorus, metals and pesticides. These pollutants are carried with the storm water and eventually make their way into our rivers and water bodies, causing sedimentation and a reduction in water quality.

Trees help to alleviate the amount of runoff by intercepting rain with their canopies. The water can be re-evaporated, or it can run down the trunk and infiltrate the soil through the tree's roots. The infiltration of water into the soil is also improved by leaf litter on the ground. As a result, more groundwater is available for other urban vegetation, and less runoff flows into our storm sewers. Even if the water does fall onto hard surfaces, the tree canopy slows it down and reduces its force. This lessens soil erosion and reduces the amount of pollutants that are picked up by the water. It also means fewer flooded streets and basements.

Trees also improve water quality by absorbing minerals and pollutants from the water that can be ecologically harmful. So the trees in the city aren't just helping keep the urban area clean and beautiful. They can have far-reaching positive consequences for the entire watershed!

Water is arguably the world's most precious resource. We use it for drinking, bathing, recreation, industry and tons of other daily activities. So let's keep the urban forest healthy to ensure that our water is squeaky clean!

Information obtained from:
http://www.forestsforwatersheds.org/reduce-stormwater/

http://www.forestry.utoronto.ca/neighbourwoods/web/

http://urbanforestrynetwork.org/benefits/water.htm
--Mara