Longevity of Bioretention Depths for Preventing Acute Toxicity from Urban Stormwater Runoff

Poster 170 – Click on poster below to view presentation from author.

Click on poster to view presentation from author.

Lane Maguire

Washington State University

Co-Authors: Jenifer McIntyre, Jay Davis

Urbanization poses increasing threats to aquatic ecosystems including increased chemical loading. The impacts of urbanization on biological integrity are especially evident in the lowland, urban streams of western North America, where adult coho salmon (Oncorhynchus kisutch) returning to spawn in the fall have been prematurely dying at high rates. Previous studies have demonstrated the effectiveness of bioretention treatment systems in treating urban stormwater runoff, thereby reducing chemical loading into surface waters, and preventing acutely lethal and sublethal effects to aquatic organisms. The current study aims to determine the effectiveness and longevity of bioretention soil media (BSM) at various infiltration depths, including those shallower the depth currently required by the Washington Department of Ecology (18”). Experimental columns, containing five different BSM depths, were dosed with roadway runoff at an accelerated rate in order to simulate six water years in approximately 15 calendar months. The chemical and biological effectiveness of the columns in treating runoff was assessed using analytical chemistry and the health of juvenile coho salmon. Bioretention treatment efficiently removed copper, zinc, total PAHs, and total suspended solids (> 70% removal). Although all treatments continued to export nitrates after six accelerated years, the export of nutrients was greatly reduced by the end of the first accelerated year. Influent stormwater runoff was acutely lethal to juvenile coho salmon (88, 90, and 100% mortality in three exposures across the six accelerated years). However, treated effluent stormwater completely prevented coho morality for all bioretention depths and for all three exposures, indicating a continued ability to prevent acute lethal toxicity after six accelerated years of treatment. This study is ongoing and will continue to assess bioretention effectiveness through 10 accelerated years.

Post comments and questions for author below.

All posts are publicly visible after review by site administrator. Students’ responses to posted questions is factored into scoring for the poster competition. Finalists announced May 25 and awards presented May 26, 2021.

5 thoughts on “Longevity of Bioretention Depths for Preventing Acute Toxicity from Urban Stormwater Runoff

  1. Cool and important project! I noticed that your stormwater looked pretty turbid, but TSS concentrations weren’t super high. How did you manage to keep the sediments in suspension in the storage tanks?

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    1. Thank you! That is a great question and something that we’ve worked to address. In the field, we recirculate the stormwater that collects in the tank that sits below the highway downspout before pumping into our transport tank. We also use a large paddle to continuously stir the water as it is being pumped into the transport tank. Back at the environmental chamber where the experimental columns are housed, we use another recirculating pump to keep sediments suspended in the tank as the columns are being dosed over a 24-hour period. All that being said, it is still difficult to ensure that sediments are making their way into the bioretention systems and that our stormwater samples are fully representative of what we’re collecting from the roadway.

      Like

    2. Thank you! That is a great question and something that we’ve worked to address. In the field, we recirculate the stormwater that collects in the tank that sits below the highway downspout before pumping into our transport tank. We also use a large paddle to continuously stir the water as it is being pumped into the transport tank. Back at the environmental chamber where the experimental columns are housed, we use another recirculating pump to keep sediments suspended in the tank as the columns are being dosed over a 24-hour period. All that being said, it is still difficult to ensure that sediments are making their way into the bioretention systems and that our stormwater samples are fully representative of what we’re collecting from the roadway.

      Like

  2. Your project is really great, hitting all the important questions! I enjoyed your presentation, too. I’m wanting to know a little more about how you determined your ‘water years’–what background data and sources of data did you use for determining that?

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    1. Thank you, David! Per our accelerated schedule, 5 water years were simulated in one calendar year. We anticipated being able to collect stormwater runoff from 30 individual storm events in one year. Based on this schedule, 6 storm events completed one ‘water year,’ defined as the period over which experimental columns were treated with the equivalent of one year of runoff. Treatment volumes per storm event were calculated based on the average annual precipitation for the city of Seattle for a 20:1 contributing area to treatment area ratio. I hope that answers your question!

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