Web Release Date: December 28,
Saturation to Improve Pollutant Retention in a Rain Garden
and
Nonpoint Education for Municipal Officials (NEMO), University of Connecticut, Middlesex Cooperative Extension Office, 1066 Saybrook Road, P.O. Box 70, Haddam, Connecticut 06438, and Department of Natural Resources Management and Engineering, University of Connecticut, 1376 Storrs Road, Unit 4087, Storrs, Connecticut 06269-4087
Received for review August 18, 2005
Revised manuscript received November 15, 2005
Accepted November 28, 2005
Abstract:
Rain gardens have been recommended as a best management practice to treat stormwater runoff. Replicate rain gardens were constructed in Haddam, CT, to treat roof runoff. The objective of this study was to assess whether the creation of a saturated zone in a rain garden improved retention of pollutants. The gardens were sized to store 2.54 cm (1 in) of runoff. Results show high retention of flow; only 0.8% overflowed. Overall, concentrations of nitrite+ nitrate-N, ammonia-N, and total-N (TN) in roof runoff were reduced significantly by the rain gardens. Total-P concentrations were significantly increased by both rain gardens. ANCOVA results show significant reductions in TN (18%) due to saturation. Redox potential also decreased in the saturated garden. Rain garden mulch was found to be a sink for metals, nitrogen, and phosphorus, but rain garden soils were a source for these pollutants. The design used for these rain gardens was effective for flow retention, but did not reduce concentrations of all pollutants even when modified. These findings suggest that high flow and pollutant retention could be achieved with the 2.54 cm design method, but the use of an underdrain could reduce overall pollutant retention.
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