Northeastern Area

The Upper Mississippi River Forest Partnership

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Trees and Watersheds: What’s the Big Deal?

Just as people and water are intertwined, so are trees and water. Besides needing the water to grow, trees help clean the water. Plants also need nutrients such as nitrogen and phosphorus to grow but too much of them is not good. High levels of nitrogen and phosphorus in water causes excessive algae growth which looks bad and can smell worse. The algae blocks sunlight, killing underwater plants that fish need. When bacteria break down the algae they can use up so much oxygen that fish suffocate. Sediment is another pollutant blocking sunlight and covering the water bottom where fish and frogs lay their eggs.

Trees help address the problems of too much nitrogen, phosphorus and sediment by:

• Slowing water flow with their roots, helping water seep into the ground, and trapping soil particles on the surface before they are washed away. Phosphorus attaches to soil particles and is also trapped.
• Taking in water through the roots. About 25% of the nitrogen in the water is taken up by the roots and used for plant growth.

Trees can also help clean the air by:

• Absorbing air-borne nitrogen.
• Absorbing carbon dioxide and using the carbon for plant growth.
• Trapping or “sequestering” carbon as a building block of the tree’s branches, leaves, trunk and roots. This carbon won’t contribute to climate change until the tree is cut down and either decomposes or is burned.