The problem

The same nutrients - phosphorus (P) and nitrogen (N) - that fertilize our lawns, also "fertilize" our river, lakes, ponds and streams. Yet our river, lakes, ponds and streams don't need fertilizing. In fact, the Assabet River and many area streams, lakes and ponds are grossly over-fertilized by nutrients, which come from storm water runoff and sewage treatment plant discharges. These excess nutrients cause aquatic plants and algae to grow like crazy in the summertime - a condition called eutrophication. This prolific plant and algal growth can ruin our waterways for boating, fishing and swimming and also harm fish and other aquatic life.

How lawns can contribute to the nutrient problem

Lawns are aesthetically pleasing and provide enjoyable places to play and relax. But they can also export significant loads of phosphorus and nitrogen to the Assabet River, local streams, lakes and ponds. How? During a storm, rain water (aka "storm water") transports phosphorus and nitrogen attached to fine soil particles, or dissolved in the rain water, from your yard to nearby waterways. Nitrate, a form of nitrogen that does not bind to soil particles, can also leach down into groundwater, particularly in sandy soils, and eventually enter streams and wetlands. In dry weather, wind can also carry nutrient-laden particles and organic matter from your yard to nearby waterways.

Sources of phosphorus and nitrogen on the lawn

Test your soil before you fertilize. Most soils already have enough phosphorus to support a lawn.

Rain and wind also transport phosphorus and nitrogen to waterways from undeveloped and uncultivated lands. Most of these nutrients enter rivers and streams attached to soil particles or contained in organic material such as dead leaves. It is a natural process. However, when people apply excess fertilizer, apply quick-release (water soluble) fertilizer, or apply fertilizer at the wrong time, rain and wind can deliver large, unnatural quantities of phosphorus and nitrogen to waterways, causing significant pollution problems.

To reduce the quantity of phosphorus and nitrogen exported from your lawn, test the soil to find out what nutrients it needs to grow grass, apply only the type and quantity of fertilizer indicated by the soil test, and keep both fertilizers and water on your lawn.

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Managing Your Lawn for a Cleaner River & Soil Tests

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Professional Help and Advice & Additional Web Resources

To learn about OAR's programs that target the Assabet's issues, check out OAR Programs.