Trees, Grass, and Clean Water: How Buffers Protect Our Lakes
By Miguel Salceda González, Ph.D.
Groundwater pollution is a serious issue that affects both the environment and human health. One major concern is nitrate-nitrite (NN), a type of pollution that comes from fertilizers and animal waste on farms. When NN enters groundwater and flows into streams and lakes, it can lead to harmful algal blooms, unsafe drinking water, and damage to aquatic life.
To address this problem, researchers studied how well different types of agroforestry buffers [areas of planted trees and grasses] could reduce NN pollution in groundwater before it reached a farm lake. Using computer models, specifically a model called MODFLOW, they ran a 10-year simulation comparing four different scenarios:
- Tree-only buffers – Rows of cottonwood trees planted along the water’s edge.
- Grass-only buffers – A mix of tall fescue, red clover, and lespedeza.
- Tree + grass buffers – A combination of both trees and grasses.
- No buffer – The control scenario, where no vegetation was planted between the farm and the lake.
The results showed that all buffers significantly reduced NN pollution compared to having no buffer. The tree-only buffer reduced NN pollution by 98%, the grass-only buffer by 97%, and the tree + grass buffer by an impressive 99%.
Buffer width also played a major role in effectiveness. When the buffer width was doubled from 15 meters to 30 meters, NN pollution dropped 16 times lower. In contrast, narrow buffers (7.5 meters) allowed nine times more pollution to reach the lake compared to 15-meter buffers.
Why do these buffers work so well? Trees and grasses help filter out pollutants before they reach the water. Plant roots absorb excess nutrients like NN, while soil microbes break down harmful compounds. Additionally, trees slow down water movement, reducing the risk of NN washing away into lakes and rivers.
This study highlights the importance of agroforestry buffers in protecting water quality. Farmers and land managers can use these findings to design more effective conservation practices, helping to keep lakes and rivers clean while maintaining productive farmland.
By planting the right combination of trees and grasses—and ensuring buffers are wide enough—farms can reduce water pollution, protect aquatic ecosystems, and promote healthier drinking water for communities.
Salceda-Gonzalez, M., Udawatta, R. P., & Appold, M. S. (2025). Groundwater Nitrate-Nitrite Modeling in a Grazed Hillslope with Agroforestry and Grass Buffers. Water, 17(5), 608. https://doi.org/10.3390/w17050608