Rainfall Runoff
DB: This is Earth and Sky. At the turn of the 20th century, only one in 10 people lived in cities. Today over half of the world’s population – well over 3 billion people – live in cities.
JB: We all know that a city’s impervious surfaces – roofs, driveways, sidewalks and streets – prevent the soil from naturally absorbing rainwater and runoff. That’s why researchers at the U.S.D.A. National Agroforestry Center are exploring a technique called “buffering” to help deal with municipal runoff and wastewater.
DB: The buffers would be strategically placed strips of land planted with native trees and edged in native shrubs and grasses. They could be placed on the outskirts of a city and fed by the city’s excess runoff. It’s thought that some native plants would be able to survive and even flourish in a buffer zone. . .
JB: . . . even though common municipal contaminants include fertilizers, petroleum and industrial and household hazardous waste. The vegetation would slow the water so it has time to soak into the soil, and – although there’s debate about this – the researchers say the soil would help naturally filter out contaminants. Topeka, Kansas is taking the lead in evaluating whether that prediction is true, and whether buffers can also decrease sky-rocketing wastewater and stormwater costs.
DB: That’s our show for today. We hope you’ll visit our web site at earthsky.com. We’re Block and Byrd for Earth and Sky.
Thanks to the following individuals who assisted in the preparation of this script:
Gregory Ruark, PhD
Director of the National Agroforestry Center
Mark Green
Water Pollution Control Division
City of Topeka
Topeka, KS
References
USDA National Agroforestry Center
Author’s Notes:
Urban buffers could provide recreational areas and cut down on urban sprawl while eliminating expensive water collection and treatment systems. In cities such as Topeka, where wastewater solids are dried to make fertilizer, buffers could also catch and naturally treat the runoff from wastewater fields.
Seventy percent of all stream and lake pollution can be attributed to runoff from agricultural areas. Manure and man-made pollutants such as fertilizers can wash into bodies of water and create a chemical imbalance, especially in the form of increased nitrogen and phosphorous. These changing nutrient levels can lead to an overgrowth of algae that eliminates the water as a source of drinking water and can deplete the oxygen available for fish and other organisms. That’s why buffers are being explored for rural areas as well. Scientists at the say that buffers of 50 to 100 feet in width could prevent up to 90 percent of agricultural pollutants from reaching the creeks and rivers.
Buffers could also secure river and stream banks against the errosion that clogs holding lakes, lowers water quality and impedes aquatic life. The shade provided by the trees in the buffer would also keep the water temperature low enough for more species of organism to thrive.
