Anthropogenic nitrogen (N) deposition has contributed to ecosystem changes across western North America including disruptions in nutrient cycling and ecosystem functioning, as well as shifts in community composition of certain organisms¹. Lands managed by the National Park Service (NPS) in the Pacific Northwest (PNW), including North Cascades National Park Service Complex (NOCA), contain ecosystems that are potentially sensitive to nutrient enrichment effects from anthropogenic N deposition². This study aims to determine the extent to which ecosystems in NOCA are being affected by N deposition and to identify predominant sources of N emissions affecting the park. Our methods involve conducting lichen community surveys and collecting lichen samples for elemental analyses including N content and N stable isotope composition. Lichens can be used as indicator organisms since the relationship between N deposition and lichen N content can be determined for a region. Lichen air quality plots were established throughout NOCA in the summer of 2018 and 2019. Data from these plots will be used to develop deposition estimates and determine the spatial extent of lichen sensitivity in the park. Since lichens are one of the most sensitive communities to N pollution within an ecosystem, assessing critical loads (CLs) based on lichens helps define maximum N deposition levels that may prevent negative impacts to the broader forest ecosystem³.