Trees and Water Quality

By Dina Haveric, Green Iowa Americorps Member

Generally, when one thinks of forests and trees, they understand the crucial role they play in purifying the air we breathe by removing harmful particles and pollutants. What one oftentimes overlooks, however, is the important role they play in keeping our water sources clean too.

Water is a valuable global resource and vital for our survival. Unfortunately, human activities are degrading the quality of the water sources we depend so greatly on. Pesticides, fertilizers, and excessive sedimentation from both agricultural and urban sources are jeopardizing aquatic communities and drinking water sources. Changes in land use also have a measurable effect on floodwater damage and frequency.

Fortunately, the strategic placement and planting of trees and forests can help alleviate these water quality issues. Trees work to improve water quality by reducing flooding, erosion, and flood damage. Tree canopies act almost like an umbrella, intercepting rainfall and slowing down its erosive energy. Interception of rainfall can also lessen the effects of a rain storm by allowing water to evaporate back into the atmosphere directly from the canopy without ever reaching the ground. Root growth and leaf litter assist in improving soil structure, enhancing water infiltration into the soil, and reducing surface runoff into our waterways. Additionally, trees can help catch or block flood debris from entering unwanted areas and trap windblown particulate matter before they enter waterways.

Another way trees work to improve our water quality is through the filtering of contaminants. Vegetation and plant debris play crucial roles in slowing down surface runoff which encourages sediment and pollutants to settle before entering surface waters. Root channels and organic matter enhances the infiltration of dissolved pollutants which are then immobilized and transformed into less harmful contaminants by microbes in the soil. It is important to note that groundwater, too, is filtered by these processes as it flows through the root zone.

Trees work to improve our water quality by enhancing aquatic habitats. Trees growing alongside bodies of water provide shade that reduces temperature changes and prevents sudden temperature fluctuations. Trees provide plant debris to aquatic systems that creates habitat and supplies food to aquatic communities. Root structures of trees help bind soil together, resulting in less runoff and more stable habitat structures. Additionally, improved infiltration of runoff from plant residues and root channels reduces the number of contaminants entering water bodies.

Trees not only service us by purifying the air we breathe, but by maintaining the health and quality of our water sources too. By planting the right trees in the right places, we can work with the forest to protect and clean our water sources.