Expert estimates of TN removal efficiencies for RSCs and bioretention cells declined with increasing storm size. For all BMP types, uncertainty in TN removal was high for all levels of precipitation. Points are median estimates and error bars encompass the 5^th and 95^th percentiles of the combined performance-based estimate. Open symbols represent BMPs in the Coastal Plain watershed; filled symbols represent BMPs located in the Piedmont watershed. Red symbols indicate TN removal efficiency for rain events preceded by a storm of identical magnitude one month earlier. Positive TN removal efficiencies represent net retention of TN by the BMP during the rain event, and negative TN removal efficiencies indicate that the BMP acted as a net source of TN during the rain event.