Effective bioretention for stormwater control

The Biological Effectiveness of Bioretention for Stormwater Pollution Control

This research addresses solutions to reducing the toxic impact of stormwater, aiming to provide better tools for managing stormwater runoff in Puget Sound.

Principal Investigator

John Stark, Puyallup Research and Extension Center, Washington State University

Co-Principal Investigators

Jay Davis, U.S. Fish and Wildlife Service

Jenifer McIntyre, Washington State University Extension

Nathaniel Scholz, NOAA Northwest Fisheries Science Center 


Bioretention is a cornerstone of low-impact development: an inexpensive, widely applicable technique for reducing runoff and removing toxins. But evaluations of bioretention have focused on physical and chemical rather than biological metrics. This project will undertake a comprehensive evaluation of its biological effectiveness. It will evaluate the effects of untreated and bioretention-treated stormwater on mortality in adult coho salmon prior to spawning, and on coho embryos and aquatic invertebrates in simulated urban streams. The goal of this work is to give local governments and other stakeholders more confidence in bioretention plans.

Research Updates

Washington Sea Grant-funded researchers used coho salmon adults and embryos to test the effectiveness of bioretention materials — 60 percent sand and 40 percent compost, overlying gravel aggregate, topped with bark mulch — in removing toxicity from runoff. The team used blood chemistry to track injury in adult coho and developed molecular tools to identify exposure and cardiac injury in developing fish.

Each type of untreated runoff killed all exposed juvenile and adult salmon within 24 hours, but all fish exposed to soil-filtered runoff survived. In addition, impacts to embryo size, development and survival were mitigated by bioretention system filtration. These exciting research results garnered significant interest from media and public officials. The research results showing effectiveness of bioretention systems has inspired an increased use of low-impact development methods in construction projects. Tableau, a Seattle software firm, redesigned their new campus to incorporate filtration of runoff from nearby Highway 99, benefiting the entire community.