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  • Spatial, Temporal, and Biological Factors Influencing Plant Responses to Deicing Salt in Roadside Bioinfiltration Basins

Spatial, Temporal, and Biological Factors Influencing Plant Responses to Deicing Salt in Roadside Bioinfiltration Basins

  • 20 Mar 2024
  • 12:00 PM - 1:00 PM
  • ONLINE: Zoom link to be provided in registration reminder email


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Spatial, Temporal, and Biological Factors Influencing Plant Responses to Deicing Salt in Roadside Bioinfiltration Basins

Presented by

 Josh Caplan, Ph.D.

Research Associate Professor

Temple University


Plants are arguably the most visible components of stormwater bioretention basins and play key roles in stabilizing soils and removing water through transpiration. In regions with cold winters, bioretention basins along roadways can receive considerable quantities of deicing salt, which may variably migrate out of the systems prior to the onset of plant growth in spring or remain in the soil. The resulting effects on plants presumably vary with time (due to annual weather patterns), space (because stormwater exposure is location-dependent), and biology (because plant taxa differ in their salt tolerance). The goal of this study was to investigate the magnitude of deicing salt’s effects on bioretention plants and how it varies with spatial, temporal, and biological factors. The study took place in a set of five bioretention basins in Philadelphia, USA that receive runoff from a major highway. Over a five-year period, the electrical conductivity (EC) of influent stormwater frequently exceeded 1 mS cm-1 in winter, occasionally surpassing that of seawater (~50 mS cm-1). In both of the years when soil EC was measured as well, it remained elevated through all spring months, especially near basin inlets and outlets. Mortality of nine plant taxa ranged widely after three years (0-90%), with rankings largely corresponding to salt tolerances. Moreover, leaf areas and/or crown volumes were strongly reduced in proportion to stormwater exposure in seven taxa. In the three taxa evaluated for tissue concentrations of 14 potentially toxic elements (Hemerocallis 'Happy Returns', Iris 'Caesar’s Brother', and Cornus sericea 'Cardinal'), only sodium consistently exceeded the toxicity limit for salt intolerant plants (500 mg kg-1). However, exceedance of the sodium toxicity limit was associated with plants’ topographic positions, with median concentrations greatest in the bottom of basins and least on basin rims. This study demonstrates that deicing salts can have detrimental effects on plants in bioretention basins, with the strongest effects likely to occur in years with the greatest snowfall (and therefore deicing salt use), in portions of basins with greatest stormwater exposure (typically around inlets and outlets), and in plants with minimal salinity tolerance. Our results therefore underscore the value of installing salt-tolerant taxa in basins likely to experience any frequency of deicing salt exposure.


Josh Caplan is an environmental biologist who specializes in plant responses to human-modified environments. He joined Temple University's stormwater team in 2017 and is now an Associate Professor of Research. Josh has helped lead investigations into plant health, evapotranspiration, and alternative soil media components. He received his PhD in 2009 through Portland State University.


This seminar does qualify for 1.0 Professional Development Hour (PDH). A Certificate of Attendance will be available for AWRA-PMAS members only. The meeting price for non-members who wish to receive a Certificate of Attendance for the PDH is $10.00 ($3.00 for meeting + $7.00 for certificate).  

Please note: 

  • Presentation Zoom link will be provided in registration reminder email.
  • Zoom link should only be used by those who register for the event through AWRA directly. 
  • PDHs will be issued through PDFs.
  • Please allow extra time to register through Zoom and get software set up.
  • Presentation will start at noon.
  • Early participants will be in a Waiting Room until noon. 
  • Participants must email to request PDH Certificate after the event.

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