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Bioretention Systems: Partial Factorial Designs for Nitrate Removal
Citation:
Gilchrist, S. AND M. BORST. Bioretention Systems: Partial Factorial Designs for Nitrate Removal. Presented at 5th Annual Ohio Stormwater Conference, SeaGate convention Center, Toledo, OH, June 06 - 08, 2012.
Impact/Purpose:
Description:
Changes in nutrient loadings are monitored by introducing captured stormwater runoff into eight outdoor rain gardens at EPA’s Urban Water Research Facility in Edison, New Jersey scaled for residential and urban landscapes. The partial factorial design includes non-vegetated mesocosms that are: small and large, anaerobic and aerobic, with and without introduced carbon source, . Time domain reflectometers and thermistors are permanently installed in the subsurfaces of the mesocosms to measure soil moisture content and temperature. Multi-parameter sondes installed in the underdrains document anaerobic conditions and time requirements for the subsurface water to become anaerobic. Mass balance results from five discrete simulated runoff events during the non-vegetated phase showed significantly larger nitrate reductions by the anaerobic mesocosms when compared with the aerobic systems. In the anaerobic mesocosms, the nitrate mass in the output water was about half that of the input while in the aerobic mesocosms the output showed twice that of the input. Mesocosm size was also important. In the anaerobic mesocosms the large mesocosms reduced nitrate mass more (Massout/Massin: 0.3) than the small mesocosms (0.7). But in the aerobic mesocosms the opposite occurred; the large mesocosms increased nitrate mass in the water by a larger factor (2.7) than the small mesocosms (1.6). In two surprising outcomes, (1) no significant differences were found for presence or absence of an introduced carbon source, and (2) nitrate mass output correlated positively with subsurface temperatures.
