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Factorial study of rain garden design for nitrogen removal
Gilchrist, S., Mike Borst, AND E. Stander. Factorial study of rain garden design for nitrogen removal. Journal of Irrigation and Drainage Engineering. American Society of Civil Engineers (ASCE), Reston, VA, 140(3):04013016, (2014).
This paper describes the reults of a mesocosm expeiroment evaluating the mass removal of (partial) speciated nitrogen. The effects of a submerged anoxic zone, an introduced wood chip layer (carbon source) and hydraulic loading are evaluated for significance using ANOVA analses,
Abstract Nitrate (〖NO〗_3^--N ) removal studies in bioretention systems showed great variability in removal rates and in some cases 〖NO〗_3^--N was exported. A 3-way factorial design (2 x 2 x 4) was devised for eight outdoor un-vegetated rain gardens to evaluate the effects of hydraulic loading (2 sizes and 2 flow rates), the presence/absence of a buried wood chip layer (2) and the presence/absence of a sub-surface saturated zone (SZ) (2) on nitrate-nitrite 〖(NO〗_3^--〖NO〗_2^-) removal. Captured stormwater runoff was used in this study. Results showed that incorporating a SZ in the design greatly reduced 〖NO〗_3^--〖NO〗_2^- mass reduction (84% compared to 5% reduction without the SZ). Presence of SZ significantly decreased ammonia-N (NH3-N) mass reduction (p<0.00001). The difference in total nitrogen (TN) mass reduction with the introduced SZ was not significant, largely due to 〖NO〗_3^--〖NO〗_2^- mass decreases that resulted in NH3-N mass increases in rain gardens with the SZ. The buried woodchip layer showed no significant effect on N removal. No significant interactions were found between the factors. Overall, the results in this study highlight the importance of incorporating a sub-surface SZ for 〖NO〗_3^--〖NO〗_2^- load reduction and that a buried woodchip layer as a carbon source did not make a significant contribution to N removal.
Record Details:Record Type: DOCUMENT (JOURNAL/PEER REVIEWED JOURNAL)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL RISK MANAGEMENT RESEARCH LABORATORY
WATER SUPPLY AND WATER RESOURCES DIVISION
URBAN WATERSHED MANAGEMENT BRANCH