Event Title

Coho Salmon Spawner Mortality in Pacific Northwest Urban Watersheds: Lethal Stormwater Impacts are Prevented by Soil Bioinfiltration

Presentation Abstract

Adult coho salmon (Oncorhynchus kisutch) return each fall to freshwater spawning habitats throughout western North America. This migration coincides with increasing seasonal rainfall, which in turn increases stormwater runoff, particularly in urban and urbanizing watersheds in the Pacific Northwest because of the land cover characteristics of these basins (e.g., increasing impervious surfaces with increased urbanization). For more than a decade, field assessments in urban streams in the greater Seattle area have shown that adult coho are dying prior to spawning, often at rates exceeding 50% of the entire fall run. The syndrome is characterized by a loss of orientation and equilibrium, leading to death on a time scale of a few hours. Such high levels of mortality are a significant concern for the long term conservation and recovery of wild coho, particularly those distinct population segments vulnerable to ongoing and future development pressures in the Pacific Northwest. Stressors related to temperature, oxygen, and pathogens have been ruled out based upon extensive forensic data. Although indirect evidence from forensic investigations and geospatial land use analyses has implicated toxic runoff as causing the mortality syndrome, this had not been directly demonstrated. Thus, we exposed otherwise healthy coho spawners to undiluted stormwater collected from a high traffic urban arterial (i.e., highway runoff) and highway runoff that was first pre-treated via bioinfiltration through experimental soil columns to remove pollutants. Results revealed that untreated highway runoff collected during nine distinct storm events over three seasons was universally lethal to adult coho relative to unexposed controls. The mortality syndrome was prevented when highway runoff was pretreated by soil infiltration. The findings demonstrate that exposure to urban stormwater is sufficient to cause the adult coho mortality syndrome. However, although the causal chemical stressor(s) have not yet been identified, conventional green stormwater infrastructure (GSI or LID technologies) can effectively protect adult spawners from the acutely toxic effects of highway runoff. Finally, integration of these types of infrastructure may protect salmonid habitat in urban watersheds.

Session Title

Bioretention Performance in the Pacific Northwest

Keywords

Keywords: habitat restoration; non-point source pollution; Pacific salmon; run-off; storm water; urban ecology; urban streams

Conference Track

Fate and Effects of Pollutants

Conference Name

Salish Sea Ecosystem Conference (2016 : Vancouver, B.C.)

Document Type

Event

Location

2016SSEC

Type of Presentation

Oral

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Comments

http://onlinelibrary.wiley.com/doi/10.1111/1365-2664.12534/abstract

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

Text

Language

English

Format

application/pdf

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Coho Salmon Spawner Mortality in Pacific Northwest Urban Watersheds: Lethal Stormwater Impacts are Prevented by Soil Bioinfiltration

2016SSEC

Adult coho salmon (Oncorhynchus kisutch) return each fall to freshwater spawning habitats throughout western North America. This migration coincides with increasing seasonal rainfall, which in turn increases stormwater runoff, particularly in urban and urbanizing watersheds in the Pacific Northwest because of the land cover characteristics of these basins (e.g., increasing impervious surfaces with increased urbanization). For more than a decade, field assessments in urban streams in the greater Seattle area have shown that adult coho are dying prior to spawning, often at rates exceeding 50% of the entire fall run. The syndrome is characterized by a loss of orientation and equilibrium, leading to death on a time scale of a few hours. Such high levels of mortality are a significant concern for the long term conservation and recovery of wild coho, particularly those distinct population segments vulnerable to ongoing and future development pressures in the Pacific Northwest. Stressors related to temperature, oxygen, and pathogens have been ruled out based upon extensive forensic data. Although indirect evidence from forensic investigations and geospatial land use analyses has implicated toxic runoff as causing the mortality syndrome, this had not been directly demonstrated. Thus, we exposed otherwise healthy coho spawners to undiluted stormwater collected from a high traffic urban arterial (i.e., highway runoff) and highway runoff that was first pre-treated via bioinfiltration through experimental soil columns to remove pollutants. Results revealed that untreated highway runoff collected during nine distinct storm events over three seasons was universally lethal to adult coho relative to unexposed controls. The mortality syndrome was prevented when highway runoff was pretreated by soil infiltration. The findings demonstrate that exposure to urban stormwater is sufficient to cause the adult coho mortality syndrome. However, although the causal chemical stressor(s) have not yet been identified, conventional green stormwater infrastructure (GSI or LID technologies) can effectively protect adult spawners from the acutely toxic effects of highway runoff. Finally, integration of these types of infrastructure may protect salmonid habitat in urban watersheds.