Root-Enhanced Infiltration in Stormwater Bioretention Facilities in Portland, Oregon
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Portland State University PDXScholar Dissertations and Theses Dissertations and Theses Winter 3-3-2017 Root-enhanced Infiltration in Stormwater Bioretention Facilities in Portland, Oregon Ted David Hart Portland State University Follow this and additional works at: https://pdxscholar.library.pdx.edu/open_access_etds Part of the Water Resource Management Commons Let us know how access to this document benefits ou.y Recommended Citation Hart, Ted David, "Root-enhanced Infiltration in Stormwater Bioretention Facilities in Portland, Oregon" (2017). Dissertations and Theses. Paper 3468. https://doi.org/10.15760/etd.5352 This Dissertation is brought to you for free and open access. It has been accepted for inclusion in Dissertations and Theses by an authorized administrator of PDXScholar. Please contact us if we can make this document more accessible: [email protected]. Root-enhanced Infiltration in Stormwater Bioretention Facilities in Portland, Oregon by Ted David Hart A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Environmental Sciences and Resources Dissertation Committee: John A. Yeakley, Chair Joseph Maser Shane Latimer Todd Rosenstiel Portland State University 2017 © 2017 Ted David Hart Abstract I evaluated the effectiveness of plant roots to increase infiltration rates within stormwater bioretention facilities (SBFs), roadside planter compartments that filter stormwater. SBFs attenuate harmful effects of stormwater by reducing peak flow and retaining pollutants, with increased infiltration that improves both these functions. Researchers have shown that roots can increase infiltration within greenhouse, lab, field, and test SBF settings. However, no researchers have yet measured either the extent to which different root characteristics can increase infiltration or the variation in root characteristics and their effect on infiltration rates among plant assemblages within currently functioning SBFs. To determine if root-enhanced infiltration was occurring within SBFs, I hypothesized 1) there is a relationship between root characteristics and infiltration during late spring, and 2) seasonal root growth increases infiltration rates. Within Portland, OR, I measured infiltration rate from January 2014 to February 2015 and root characteristics from January- February (J-F) and May-June (M-J) 2014 in ten SBFs with “Elk Blue” rush (Juncus patens) and 1 or 2 trees of less than 8.4 cm stem diameter. During M-J, four root characteristics showed a positive relationship with infiltration rate, and two root characteristics showed a strong positive relationship with infiltration rate within the topsoil. Also, a relationship was shown between the increase (J-F to M-J 2014) in three root characteristics and the increase in infiltration rate. i To determine if root morphology and infiltration rates differed among SBFs with two different dominant vegetation taxa (small and large root biomass), I hypothesized 3) Juncus patens and tree dominant assemblage (greater root biomass) exhibits greater infiltration compared to the Carex dominant assemblage, 4) the increase in infiltration rate and root characteristics from J-F to M-J is greater in the Juncus compared to the Carex assemblage, and 5) root surface area density (RSAD) within Juncus SBFs shows a positive relationship with infiltration rate in late spring. I measured infiltration rate from January 2014 to February 2015 and root characteristics from January-February (J-F) and May-June (M-J) 2014 among five large-root (Juncus and tree) and five small-root biomass (Carex sp) SBFs. Juncus SBFs showed greater values for three root characteristics during J-F and five root characteristics during M-J 2014 compared to Carex SBFs. Also, Juncus SBFs showed an increase from J-F to M-J 2014 for five root characteristics while Carex SBFs showed no root increase. Juncus SBFs showed a relationship with four root characteristics and Carex SBFs a showed relationship with one root characteristic and infiltration rate. This work strongly suggests plant roots increase infiltration, and thus the primary functions of SBFs. Different root characteristics appear to increase infiltration rate at different depths. Data also show larger-root biomass plants increase infiltration rate to a greater degree than smaller-root biomass plants. I recommend considering several site and facility characteristics when determining the potential for root-enhanced infiltration. When selecting plant species to enhance infiltration, I recommend using several criteria, determining root characteristic ii values at certain depths, considering installation approaches, and accounting for regional climate changes. iii Acknowledgements I would like to thank my advisor, Dr. Alan Yeakley, for the all the support including the numerous words of wisdom, use of his lab space for my office and root processing and analysis, use of his computers for hydrological analysis, help modeling, and numerous other contributions over the past several years. I would like to also thank Dr. Joseph Maser for his guidance and help in developing my research during the first years of my degree. He was always a steadfast and understanding supporter. I would like to thank Dr. Todd Rosenstiel for steering me in the direction of in situ root and infiltration measurements as this has greatly increased my knowledge of bioretention facilities and my connections in this field. I would like to thank Dr. Shane Latimer who has always generously offered sage advice. He has provided a necessary real-word perspective to my research greatly enhancing its value. I would like to thank Dr. Martin LaFrenz who helped me during the initial phase of my dissertation project. I would like to thank Josh Caplan who provided valuable assistance and advice analyzing roots. Josh also provided numerous phone calls to determine the most scientifically rigorous and valuable methods for representing root characteristics. I would like to thank all the City of Portland Bureau of Environmental Service (BES) personnel who supported this project: Henry Stevens, Tim Kurtz, Denis O’Brien, Jeff Tilton, and Jordan McCann. I would like to thank all the technicians with whom I have worked and who helped me along the way. I am thankful that Liz Olney led the first investigation of root characteristics in Portland bioretention facilities. Alex Desroches was a supportive and iv enthusiastic friend and collected much data and I’m grateful for his help. Steven Murschel has been a stalwart coworker during times when I needed him most and I most grateful to him for that. Jonathan Hawkes provided much enthusiastic work. Mathew Przyborski was always a pleasant and eager person to work with. Chris Parker provided much good advice. I would like to thank the funding sources for this work: Urban Long-Term Research Area (ULTRA, NSF grant number #0948983), Portland State University (PSU) Cascades to Coast GK12 Project (NSF grant number #0948041), the City of Portland Bureau of Environmental Service (BES), and Portland State University. v Table of Contents Abstract ............................................................................................................................. i Acknowledgements ............................................................................................................ iv List of Tables ................................................................................................................... viii List of Figures ......................................................................................................................x Chapter 1 Introduction .........................................................................................................1 Chapter 2 Evidence for Root-enhanced Infiltration within in situ Stormwater Bioretention Facilities in Portland, OR .............................................................17 Abstract ......................................................................................................................... 17 Introduction ................................................................................................................... 18 Methods ......................................................................................................................... 22 Results ........................................................................................................................... 30 Discussion ..................................................................................................................... 51 Chapter 3 Root Characteristics and Infiltration among Stormwater Bioretention Facilities with Different Vegetation Assemblages ............................................................60 Abstract ......................................................................................................................... 60 Introduction ................................................................................................................... 62 Methods ......................................................................................................................... 66 Results ........................................................................................................................... 75 Discussion ..................................................................................................................... 88 Chapter 4 Management Implications and Summary .........................................................94