Model analysis and visualization of 6PPD-quinone fate and transport in Longfellow Creek watershed, Seattle, USA
· Transport of materials from the landscape controls nearshore water quality in most estuarine and coastal ecosystems, including Puget Sound. A prevailing assumption is that nearshore and coastal water quality can be improved through effective land use policies designed to minimize pollutant runoff. Examples include requirements that green infrastructure such as rain gardens, and gray infrastructure such as stormwater vaults, be included in new and updated development projects. Developing such policies and strategies requires understanding the relationships between the kinds, amounts, and spatial distribution of green and gray infrastructure and resulting loadings of water, sediments, pathogens, and chemical pollutants. This presentation focuses on applications of the US EPA’s VELMA ecohydrological model for assessing the effectiveness green and gray infrastructure improvements for reducing stormwater contaminant loads to Seattle’s Longfellow Creek. This creek, like many other urban creeks draining to Puget Sound, experiences high rates of coho salmon prespawn mortality associated with lethal concentrations of 6PPD-quinone, a breakdown product of 6PPD contained in tire-wear particles (Tian et al. 2020). Details of the hydrological and biogeochemical processes controlling spatial and temporal dynamics of 6PPD-quinone fate and transport from points of deposition to stream and estuary are poorly understood. Here we present initial VELMA model results to elucidate these processes for the Longfellow Creek watershed (1,087 ha). Results include high-resolution (10-m) spatiotemporal animations of 6PPD-quinone fate and transport for various alternative green and gray infrastructure treatments.