How Do Rain Gardens Reduce Nutrient Pollution?
Nutrients such as nitrogen and phosphorus – some of the most abundant elements in fertilizers – can become pollutants once they are washed into our waterways. Under the right circumstances, excess nutrients in these ecosystems can trigger abnormally large algal blooms that deplete resources like oxygen and sunlight at the expense of other wildlife. Rain gardens can help reduce or even stop nutrients from reaching our waterways by channeling runoff into the center of the garden. The water can soak into the ground before it would otherwise flow over saturated soils, down a storm drain and into a stream or river. The garden’s soil layers can filter impurities (like nitrogen and phosphorus) from the water like a stack of strainers and sifters. Once in the soil, these nutrients are used by the rain garden’s plant life and other impurities can be chemically transformed by bacteria, microbes and other decomposers.
Viewer Tip: If you plan on installing a rain garden in your own yard, follow these steps to maximize its effectiveness. You can learn more about designing rain gardens at cfpub.epa.gov/npdes/stormwater/menuofbmps/index.cfm?action=browse&Rbutton=detail&bmp=72.
- Siting: Site placement is a very important consideration. Also, it is critical to determine where underground utilities may be buried so that they can be avoided. Select places in your yard where water often pools. If you’re landscaping the yard from scratch, dig a depression into the ground with gradual slopes that are less than five degrees.
- Treatment: To maximize filtration efficiency, design a buffer of small stones or other coarse material along the garden’s edge. Use a sand/soil mixture for the garden bed with a layer of mulch on top.
- Landscaping: Plant the garden with native plants, shrubs and even trees. Use species that survive in or prefer wet soils at the center of the garden with other species near the edges.
(Sources: U.S. Environmental Protection Agency. “Act: In Your Yard.” Accessed Online May 3, 2012. http://www.epa.gov/nutrientpollution/whatyoucando/act_inyard.html; U.S. Environmental Protection Agency. “National Pollutant Discharge Elimination System: Bioretention (Rain Gardens).” Accessed Online May 3, 2012)