Modelling impacts to water quality in salmonid-bearing waterways following the introduction of Emerald Ash Borer in the Pacific Northwest, USA.

Abstract

Abstract Oregon ash (Fraxinus latifolia Benth.) wetlands and riparian forests are an important economic, cultural, and ecological resource in the Pacific Northwest, USA, and are threatened by the invasive insect, emerald ash borer (Agrilus planipennis Fairmmaire) (EAB). Following the discovery of EAB in Forest Grove, Oregon in June of 2022, concern has focused on EAB-induced ash mortality that has the potential to alter vegetation communities and modify wetland hydrology by elevating the water table. Of primary concern is an increase in solar loading of waterways and wetlands that are already degraded beyond meeting their beneficial uses for Endangered Species Act-listed salmonids and other cold-water species following canopy dieback of Oregon ash. Our study, begun before the first detection of EAB on the West Coast, models potential impacts of EAB-mediated Oregon ash canopy loss to temperature-related water quality on two waterways in the vicinity of Portland, Oregon. Our results indicate a significant increase in solar loading with likely negative impacts to aquatic Endangered Species Act-listed salmonids, other aquatic wildlife, and associated habitat. We forecast greater impacts to these resources outside our study scope and include management considerations and recommendations for entities with water quality-related regulatory obligations.