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Factorial study of rain garden design for nitrogen removal
Citation:
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).
Impact/Purpose:
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,
Description:
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.
