Floating Treatment Wetland and Biomedia Module for StormwaterTreatment and 6PPD Quinone Removal

Despite decades of estuarine and river restoration efforts, effectiveness monitoring surveys continue to document premature mortality of coho salmon (Oncorhynchus kisutch) within the streams of urbanized areas in the Pacific Northwest (PNW).Many researchers have identified stormwater inputs, especially road runoff, to be a primary cause of salmon mortality and poor recruitment while other researchers have found that certain stormwater bio-infiltration methods helped reduce mortality significantly.In December of 2020, 6PPD quinone, a previously unknown chemical derived from tire wear particles, was identified as the particularly potent contaminant responsible for killing coho salmon.Traditional biofiltration measures have been shown to alleviate the toxicity of the stormwater on salmon, however, many highly urbanized areas of Puget Sound cannot accommodate bioswales or green infrastructure for the treatment of road runoff before entering urban streams.For these sites where other types of green infrastructure is impractical, using a mesocosm design experiment, we examined the potential of using floating treatment wetlands (FTWs) with biomedia within as an in-situ treatment for stormwater contaminants including 6PDD quinone.We analyzed three biomedia mixes for the ability to adsorb stormwater contaminants, especially 6PPD quinone resulting in reductions of 82%, 81%, and 86% respectively for each biomedia mix tested.We then investigated the efficacy of the most beneficial wetland species planted within FTWs and the most efficient biomedia mix on the reduction of stormwater contaminants (from this point forward including 6PPD quinone) and coho salmon survival.The results were efficacious with a 79% reduction in 6PPD quinone and 100% survival and no symptoms of 6PPD quinone for any of the coho salmon in the treated stormwater.Further deterioration of coho populations risk extinctions within those streams and rivers in high urban environments, reducing overall genetic diversity of the species.