Meaghan gave an excellent talk at the National Atmospheric Deposition meeting!

Assessing nitrogen critical loads at North Cascades National Park Service Complex 

Meaghan Petix1, Michael D. Bell2, Tonnie Cummings3, Alida Melse4 and R. Dave Evans5

Anthropogenic nitrogen (N) deposition (Ndep) contributes globally to disruptions in nutrient cycling, ecosystem functioning, and shifts in community composition. National Park Service (NPS) lands, including the North Cascades National Park Service Complex (NOCA), contain ecosystems that are potentially sensitive to Ndep. Accurate measurements of Ndep are needed to determine N critical loads, levels of Ndep that can be sustained without adverse biological effects. However, in the western U.S., complex topography and weather patterns can lead to difficulty in accurately estimating Ndep with predictive models. The N concentration of epiphytic lichens can be utilized to monitor Ndep because the relationship between lichen N concentration and Ndep can be modeled for a given region.

The goal of this study is to assess patterns of Ndep in NOCA and determine which ecosystems are affected by Ndep. We established 30 plots across NOCA to determine lichen community composition and N content and stable isotope composition in the summer of 2018 and 2019. Lichen N content (% dw) varied between 0.25 and 0.49 and estimated throughfall total inorganic Ndep spanned a range from 0.10 to 0.63 kg N ha-1 year-1, indicating low levels of Ndep throughout the park. We found levels of Ndep increased moving east in the northern portion of the park. There was not a strong relationship for lichen N content along an elevational gradient. Results will be incorporated with lichen community composition and atmospheric chemistry models in a GIS framework to develop a powerful approach to evaluate N critical load exceedance in the North Cascades. Integration with U.S. Forest Service (USFS) lichen air quality datasets will allow for further assessment of patterns of Ndep across the region.

1Washington State University, meaghan.petix@wsu.edu 2NPS Air Resources Division, michael_d_bell@nps.gov 3NPS Pacific West Region, tonnie_cummings@nps.gov 4Washington State University, alida.melse@wsu.edu 5Washington State University, rdevans@wsu.edu