VELMA model green infrastructure applications for reducing 6PPD-quinone concentrations in Puget Sound urban streams.
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Coho salmon (Oncorhynchus kisutch) are highly sensitive to 6PPD-Quinone (6PPD-Q). The processes controlling spatial and temporal dynamics of 6PPD-Q fate and transport from points of deposition to receiving waters are poorly understood. To understand the fate and transport of 6PPD-Q and mechanisms leading to salmon mortality, Visualizing Ecosystem Land Management Assessments (VELMA), an ecohydrological model developed by U.S. Environmental Protection Agency (EPA), was enhanced to better understand, and inform stormwater management planning by municipal, state, and federal partners seeking to reduce stormwater contaminant loads in urban streams draining to the Puget Sound National Estuary. Model results highlight hydrological and biogeochemical controls on 6PPD-Q flow paths and hotspots within the watershed and its stormwater infrastructure, that ultimately impact contaminant transport. Most importantly, VELMA’s high-resolution spatial and temporal analysis of 6PPD-Q hotspots provides a tool for prioritizing the locations, amounts, and types of green infrastructure (GI) that can most effectively reduce 6PPD-Q stream concentrations to levels protective of coho salmon and other aquatic species. Here we present a series of theoretical installations of GI at and downstream of model identified hotspots. Each GI installation has both an estimated installation cost and quantified ecological benefit as reduced 6PPD-Q instream loading compared to the No-GI baseline simulation. This modeling approach is presented as a decision support framework to 1) ensure the management action, or coupled actions, will sufficiently reduce 6PPD-Q to protective levels, while 2) comparing each management action’s economic cost. VELMA’s high-resolution spatial and temporal analysis of 6PPD-Q hotspots demonstrates the capabilities of this tool and approach for prioritizing the locations, amounts, and the kinds of GI among those tested in the scenarios that can most effectively reduce 6PPD-Q stream concentrations to levels protective of coho salmon and other aquatic species.