Feraud, MarinaAhearn, Sean P.Parker, Emily A.Avasarala, SumantRugh, Megyn B.Hung, Wei-ChengLi, DongVan De Werfhorst, Laurie C.Kefela, TimnitHemati, AzadehMehring, Andrew S.Cao, YipingJay, Jennifer A.Liu, HaizhouGrant, Stanley B.Holden, Patricia A.2024-02-262024-02-262022-12-170043-1354S0043-1354(22)01446-4 (PII)https://hdl.handle.net/10919/118153Nitrogen (N) in urban runoff is often treated with green infrastructure including biofilters. However, N fates across biofilters are insufficiently understood because prior studies emphasize low N loading under laboratory conditions, or use “steady-state” flow regimes over short time scales. Here, we tested field scale biofilter N fates during simulated storms delivering realistic transient flows with high N loading. Biofilter outflow ammonium (NH4+-N) was 60.7 to 92.3% lower than that of the inflow. Yet the characteristic times for nitrification (days to weeks) and denitrification (days) relative to N residence times (7 to 30 h) suggested low N transformation across the biofilters. Still, across 7 successive storms, total outflow nitrate (NO3−-N) greatly exceeded (3100 to 3900%) inflow nitrate, a result only explainable by biofilter soil N nitrification occurring between storms. Archaeal, and bacterial amoA gene copies (2.1 × 105 to 1.2 × 106 gc g soil−1), nitrifier presence by16S rRNA gene sequencing, and outflow δ18O-NO3− values (-3.0 to 17.1 ‰) reinforced that nitrification was occurring. A ratio of δ18O-NO3− to δ15N-NO3− of 1.83 for soil eluates indicated additional processes: N assimilation, and N mineralization. Denitrification potential was suggested by enzyme activities and soil denitrifying gene copies (nirK + nirS: 3.0 × 106 to 1.8 × 107; nosZ: 5.0 × 105 to 2.2 × 106 gc g soil−1). However, nitrous oxide (N2O-N) emissions (13.5 to 84.3 μg N m −2 h −1) and N2O export (0.014 g N) were low, and soil nitrification enzyme activities (0.45 to 1.63 mg N kg soil−1day−1) exceeded those for denitrification (0.17 to 0.49 mg N kg soil−1 day−1). Taken together, chemical, bacterial, and isotopic metrics evidenced that storm inflow NH4+sorbs and, along with mineralized soil N, nitrifies during biofilter dry-down; little denitrification and associated N2O emissions ensue, and thus subsequent storms export copious NO3−-N. As such, pulsed pass-through biofilters require redesign to promote plant assimilation and/or denitrification of mineralized and nitrified N, to minimize NO3−-N generation and export.11 page(s)application/pdfenCreative Commons Attribution 4.0 InternationalPollutant RemovalBioretentionDenitrificationPerformanceProkaryotesNutrientNitratesNitrogenNitrous OxideAmmonium CompoundsSoilSoil MicrobiologyDenitrificationNitrificationArticle - Refereedhttps://doi.org/10.1016/j.watres.2022.119501230Grant, Stanley [0000-0001-6221-7211]365875191879-2448