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Improving Local Water Quality Through Lawn Conversion

Vincent Cotrone, Penn State Extension​   Aug 6, 2020 Updated 22 hrs ago


Don’t get me wrong, I like walking on turf in my backyard and local parks or watching my children play soccer or some other sport on athletic turf, but mowed lawns have become a larger and larger land cover over the past 30 years or so. They seem harmless and green, but we have learned that managed lawns have a greater impact on our water quality than forests and meadows.

You might ask, “what is the harm in growing grass?” Well, it really depends on how much of your yard is turf and how you manage it. When we look at statistics compiled by Peter Claggett, USGS Research Geographer, we find that lawns or turfgrass is the largest crop grown in the Chesapeake Bay watershed, accounting for 9.5% of the land cover or 3.8 million acres. The best estimate for how much nitrogen fertilizer is applied to lawns in the Chesapeake Bay watershed is nearly 215 million pounds per year. This is enough nitrogen to grow nearly 2 million acres of corn. About 19 million pounds of pesticide active ingredients, mostly herbicides to kill “weeds,” are used each year. These fertilizers and pesticides are reaching local streams and rivers causing harm to aquatic life.

We spend more and more time mowing acres of grass around suburban homes each year. According to the US Department of Energy, Americans use 1.2 billion gallons of gasoline for lawn mowing annually. Besides lawnmower exhaust contributing to air pollution, some of that gasoline gets spilled as we attempt to fill our mowers, adding more pollutants to our waterways.

With urban and suburban nutrient and water pollutant loads on the increase, making some small changes can go a long way to improving water quality for local streams and the Chesapeake Bay. Research has shown that areas that are forested or have good tree cover export nutrients to waterways. According to the Chesapeake Bay Expert Panel Report on Tree Canopy Expansion as an Effective Best Management Practice, an acre of trees or forest contributes 1.68 lbs of nitrogen to local streams annually, while the same acre managed in turf contributes 11.19 pounds each year. Phosphorus loading rates for turf are 0.86 lbs/acre/year while a forested acre contributes only 0.08 lbs/acre/yr. Just by converting turf to a forested setting, we can typically see an 85% reduction in nitrogen and a 91% reduction in phosphorous that is exported or leached to local streams. The nutrient reduction benefit results from the conversion of turf or impervious land into tree canopy or forest, which reduces runoff by intercepting rainfall and promoting soil infiltration, where the nutrients can deposit in the soil and be taken up by tree roots.

Even planting trees in your yard with turf grass below them or planting a street tree that will cover the road with its canopy will reduce nutrient loads according to research by Hynicka and Divers in 2016.

These trees provide many benefits beyond water quality improvements. Trees help:

• Improve air quality by catching particulate matter and absorbing air pollutants.

Reduce urban temperatures by shading roads, parking lots, sidewalks, and rooftops.

• Help mitigate climate change by absorbing greenhouse gases.

• Serve as an important wildlife habitat for birds and insects.

• Enhance the aesthetic value, increase property values, and increase recreational opportunities within the community.

The Alliance for the Chesapeake Bay is currently piloting a new program in parts of Pennsylvania to assist landowners that are interested in converting mowed turf areas to either meadows or forested areas. The Lawn Conversion Program will cover the cost of converting areas of lawn that are at least half an acre when landowners sign an agreement to retain and manage a meadow for 5 years after planting and a forested area for 10 years after trees are planted. The Alliance will handle all the preparation and planting. Landowners can plant trees and shrubs for marketable goods such as fruit, nuts, syrups, and florals. With reduced mowing, both time and money will be saved by landowners that convert a half acre or more, not to mention the water quality benefits, wildlife and pollinator habitat produced, aesthetic improvements, and energy conservation (shade from trees, less gasoline and air pollutants from lawnmower)