Browsing by Author "Holden, Patricia A."

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    Perceived services and disservices of natural treatment systems for urban stormwater: Insight from the next generation of designers
    Rippy, Megan A.; Pierce, Gregory; Feldman, David; Winfrey, Brandon; Mehring, Andrew S.; Holden, Patricia A.; Ambrose, Richard; Levin, Lisa A. (Wiley, 2022)
    1. Natural treatment systems (NTS) for stormwater have the potential to provide a myriad of ecosystem services to society. Realizing this potential requires active collaboration among engineers, ecologists and landscape planners and begins with a paradigm shift in communication whereby these groups are made aware of each other's perceptions about NTS and the presence of knowledge gaps that their respective disciplines can bridge. 2. Here we participate in the first part of what we hope will be a reciprocal exchange: presenting results from a landscape perceptions survey to urban planners, ecologists and landscape architects that illustrates how the next generation of engineers perceives NTS relative to other landscape features, and the implications of those perceptions for future infrastructure development. 3. Our results suggest that although lawns, gardens and native ecosystems were perceived as multifunctional, providing characteristic bundles of services/disservices, perceptions of NTS were more variable (i.e. there was no social norm for their perception). 4. Environmental worldviews, knowledge, attitudes about ecosystem services and demographics were all significant drivers of perceived services. However, students had difficulty identifying NTS correctly, and factual knowledge about NTS did not help students associate NTS with typical design services like flood reduction more than features not designed for those purposes, such as lawns. This suggests that engineering students lack familiarity with the outward appearance of NTS and have difficulty placing NTS services into a broader landscape context. 5. Expertise from urban planning and ecology could help bridge these knowledge gaps, improving the capacity of tomorrow's engineers to co-design NTS to meet diverse community needs.
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    Stormwater biofilter response to high nitrogen loading under transient flow conditions: Ammonium and nitrate fates, and nitrous oxide emissions
    Feraud, Marina; Ahearn, Sean P.; Parker, Emily A.; Avasarala, Sumant; Rugh, Megyn B.; Hung, Wei-Cheng; Li, Dong; Van De Werfhorst, Laurie C.; Kefela, Timnit; Hemati, Azadeh; Mehring, Andrew S.; Cao, Yiping; Jay, Jennifer A.; Liu, Haizhou; Grant, Stanley B.; Holden, Patricia A. (Pergamon-Elsevier, 2022-12-17)
    Nitrogen (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.