Trees & Our Waterways

Most people know that trees work to purify the air we breathe by absorbing carbon dioxide and other harmful gases to produce oxygen. However, the multitude of benefits trees provide to our water sources is far less known but still just as important for maintaining healthy waterways.

Pennsylvania is made up of nearly 83,000 miles of rivers and streams and they provide us with a wide array of uses from recreation to drinking.  As we continue to industrialize, we add more impervious surfaces such as roads, parking lots, houses, etc. to the landscape.  Because of this, water travels more quickly across impervious surfaces and doesn’t soak into the ground as it normally would. This occurrence is called stormwater runoff and as it travels it gains speed and picks up contaminants before the increased volume of water makes its way to a nearby waterbody. Because the runoff makes it to the water so quickly, the waterbody is sometimes unable to handle the large influx and can cause flooding, erosion, and/or poor water quality due to sedimentation.

Trees first affect the flow of stormwater runoff when the leafy tree canopy intercepts the rainfall before it hits the ground. This interception slows the speed of the water running into waterways and therefore protects against bank erosion and flooding. Trees and the ground also work to absorb precipitation before it makes its way to the waterbodies. According to Penn State, the permeable ground can typically absorb up to 18 inches of precipitation before gradually releasing it to natural channels and recharging ground water. Trees also need to absorb water to grow, a typical tree can soak up 100 gallons of water a day which leads to evapotranspiration (when water is absorbed and eventually released into the air by trees and plants) which keeps the temperature regulated and cooler in the summer, according to North Carolina State University.

Lastly, woody plants are excellent at removing nitrates, phosphates, and various contaminants from the soil and water. A Maryland study showed reductions of up to 88% of nitrate and 76% of phosphorus after agricultural runoff passed through a forest buffer.

It is because of these reasons that many organizations plant riparian forest buffers. RFBs are a combination of carefully selected trees, shrubs, grasses that are planted alongside a stream or river. Penn State attests “Riparian forest buffers filter sediment from streams during storm events; remove nitrogen and phosphorus leaching from adjacent land uses such as agriculture; provide stability to the bank (wood root systems); shade and modify stream temperatures, critical for habitat and pollution reduction; provide aquatic and wildlife habitat for many species; reduce stream velocity; and reduce downstream flooding” 

Trees are a integral part of our ecosystems, they work to keep systems cohesive and purify our air, water, and land. It is because of this that we should protect our trees because of the many benefits they provide for our health, as well as our enjoyment.


  A diagram of a typical Riparian Forest Buffer. Photo from Southeast Michigan Resource Conservation & Development Council.

A diagram of a typical Riparian Forest Buffer. Photo from Southeast Michigan Resource Conservation & Development Council.

Marissa Rollman