Nutrient Leaching from Bioretention Amended with Source-Separated Compost

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Bioretention has been noted to be an effective stormwater control measure (SCM). Compost addition to bioretention could be beneficial, but could also act as a source for excess nutrients. This project analyzed possible nitrogen (N) and phosphorus (P) leaching from bioretention soil media (BSM) amended with source-separated compost. Columns were mixed with compost and BSM at volumes of 30%, and 15%. A final column had 15% compost and an additional 4% water treatment residual (WTR). Synthetic stormwater was applied to each column and the effluent was analyzed for N and P. The 30% column increased the mass exported for both nutrients. Both 15% columns had a net zero effect on nitrogen, but the 15%+WTR column reduced the exported phosphorus load. All compost columns discharged more nutrients than standard BSM. Compost addition should be minimized in bioretention, less than 15% by volume, and WTR should be added to control phosphorus leaching.