The National Park Service (NPS) is a United States agency established in 1916, that works with all national parks and memorials across the nation. This report series evaluates the relative sensitivity of National Park Service parks and inventory & monitoring networks to potential nutrient enrichment effects caused by atmospheric nitrogen deposition. Such effects can be caused by the addition of oxidized nitrogen (NOx) and/or reduced nitrogen (NHx) to natural ecosystems. Nutrient nitrogen enrichment can occur in both terrestrial and aquatic ecosystems. Nitrogen from air pollution sources can alter plant and algal communities and affect biodiversity.