Anthropogenic emissions of nitrogen can travel long distances to be deposited in remote, pristine ecosystems. Thin soils, short growing seasons, and steep terrain make alpine ecosystems especially sensitive to the effects of even moderate amounts nitrogen deposition. Critical Loads of N for alpine areas for changes in vegetation communities (3.0 kg N ha-1 yr-1) and soil leaching (10.0 kg N ha-1 yr-1) have been established in Colorado. Even though the research was done outside of National Park boundaries, alpine provide a multitude of ecosystem services and natural resources that are important to protect. Thus, we extrapolated the critical loads to alpine areas within parks to inform current risk to alpine systems and how that has evolved over the past several decades. We used the USGS GAP dataset to identify alpine areas within national park units and compared the alpine critical loads to the NADP Total Deposition Model received from 2000-2002 and from 2014-2016 to determine how exceedances have changed over time. 

We found that 24 of the 28 park units that had alpine area received total deposition greater than the alpine vegetation critical load of 3.0 kg N ha-1 yr-1. Of these park units, 22 of them exceeded the critical load in 75% or more of their alpine area. However, only Sequoia Kings Canyon National Park received deposition greater than the unvegetated critical load of 10.0 kg N ha-1 yr-1. The maximum total deposition the park units are receiving is on an overall decline, where 20 of the parks experienced lower maximum deposition in 2016 than they did in 2002. Most of the parks didn’t show a large change in percent exceedance from the 2000 – 2002 average to the 2014 – 2016 average, but Olympic National Park and Mount Rainier National Park showed a 57% and 19% decrease in area exceeded, respectively. Crater Lake National Park showed the only noticeable increase in percent exceedance (13%) over the time period. These results can help park managers identify which alpine areas potentially at risk of change due to deposition and help guide restoration and policy actions in exceeded areas