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GREENROOF RUNOFF WATER QUALITY
Citation:
BERGHAGE, D., D. BEATTIE, A. JARRETT, AND T. OCONNOR. GREENROOF RUNOFF WATER QUALITY. In Proceedings, Fifth Annual International Greening Rooftops for Sustainable Communities Conference, Awards & Trade Show, Minneapolis, MN, April 29 - May 01, 2007.Green Roofs for Healthy Cities (GRHC), Toronto, ON, CANADA, ,, (2007).
Impact/Purpose:
To share information
Description:
Runoff samples were collected from 5 experimental green roof test plots on small buildings at the Center for Green Roof Research at Rock Springs, PA during the period from January 2005 through May 2006. Samples were either analyzed in-house for pH, Electrical Conductivity (EC), Turbidity, Color, and Nitrate and/or were tested for various plant nutrients and other ions using an ICP in the Penn State Agricultural Analytical Laboratory. Ions evaluated by ICP were Calcium, Cadmium, Copper, Iron, Potassium, Magnesium, Manganese, Molybdenum, Sodium, Nickel, Phosphorous, Lead, and Zinc. In addition samples from 2 events were analyzed for Sulfur. Runoff nutrient loadings in pounds per acre were calculated from measured concentrations and measured runoff quantities. Sampled precipitation events ranged from 0.07 in. on 3/4/05 to 3.2 in. on 10/8/05. Total precipitation from the sampled storms was 16.15 in. Sampled events included rain, snow and freezing rain. Runoff water quality varied with both sampled event and roof type. The most noticeable difference between runoff from the green roofs and runoff from an equivalent flat roof was the color of the water, which was yellow for the runoff from green roofs. The pH was consistently higher in runoff from green roofs. Nitrate nitrogen concentration in runoff from green and non-green roofs varied but was not significantly different on average over the study period. Total quantity of nitrate in the runoff from the green roofs was in contrast, greatly reduced compared to non-green roofs (1 lb per acre of roof vs. 4.7 lb per acre from non-green roofs for the sampled storms or a difference of about 11 lb per acre for an average annual precipitation of 44 in). Concentrations for other nutrients and ions in runoff solution and total quantity in the runoff varied, with some nutrient loadings higher, the same, or lower in runoff from green vs. non-green roofs.
