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Posted on: May 20, 2020

Greening West Goshen: Understanding the Link Between Fertilizer and Stream Health

Few moments in life are more mesmerizing than watching clear stream water flow over pebbles, under logs, and through chutes and riffles. We notice the colors, the play of light and shadow, and minnows swimming freely. 

In Pennsylvania, healthy streams exist where the input of nutrients is well-matched to the needs of the diverse populations of plants, animals, and microlife. This balance is disturbed by excess fertilizer carried in runoff from our lawns, gardens, and pavement. Other sources of excess nutrients include agricultural and septic systems, soil erosion, and pet waste. Most fertilizers are synthetic and contribute to this problem by quickly releasing their nutrients; extended-release formulations do exist, however. In 2008, a regional laboratory of the  Environmental Protection Agency (EPA) found that 40-60% of lawn fertilizer is carried to surface water and groundwater2

In particular, the growth of algae is enhanced by the nitrogen and phosphorus of fertilizers. According to Dr. Marc Peipoch of the Stroud Water Research Center in Avondale, limited amounts of algae like Cladophora can be helpful in providing aquatic food and shelter. However, “too much [algae] becomes a problem”3. If the supply of nutrients exceeds the stream’s needs, filamentous algae may proliferate, taking up space, blocking light, and degrading the habitat in other ways. Algae can also cause water to develop a toxic alkalinity. As algae die and feed bacteria in the water, it may lower dissolved oxygen to levels insufficient for fish and other life. 

Streams are also part of watersheds, so fertilizer runoff into Goose Creek, for example, affects Chester Creek, the Delaware Bay and, gradually, the Atlantic Ocean. This affects our quality of life in several areas including drinking water treatment, fishing, swimming, and boating.

We can prioritize clean and clear water through the careful management of fertilizers. But how can you control the amount of excess nutrients in runoff from your property? 

  1. Consider alternative species, such as self-fertilizing microclovers, for spaces to be used as lawn and pathways.⁴ You might want to devote space to a vegetable garden, berry patch, and/or provide habitat to support pollinators and birds. With insects and birds in rapid decline, land owners have both an opportunity and a responsibility to nurture life on their properties. Growing native plants for new meadows and woodland pockets help to reverse these losses. A property  made up of 30% nonnative plants would develop into one of diverse beauty.⁵
  2. Let grass clippings, an excellent source of nitrogen, feed your lawn, reducing the need for fertilizer by between 25% and 50%¹² One or two inches of grass clippings can also make a great mulch. Do not let the grass clippings touch plants, and be sure not to use them if toxins have been applied to the lawn. 
  3. If needed, select a slow-release form of nitrogen fertilizer which takes longer to break down in the soil and is less likely to leach out in the first rain. Request a phosphorus-free fertilizer unless a soil test determines that phosphorus is lacking in your soil. A sample of your soil can be mailed to Penn State Extension and analyzed for a nominal charge.
  4. Be careful not to over fertilize. Minimize the frequency of application. Never apply when rain is in the forecast.

By John Davis, PhD, PE, Associate Professor, Department of Civil Engineering, Widener University for the Chester-Ridley-Crum Watersheds Association, and Eunice Alexander, Township Parks and Recreation Board


  5. Tallamy, D.W. 2019. Nature’s Best Hope:  a new approach to conservation that starts in your yard. Portland, OR: Timber Press.

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