Ammonia Emissions from Subalpine Forest and Mountain Grassland Soils in Rocky Mountain National Park

Atmospheric deposition of NH₃ and NH₄⁺ contributes to eutrophication within sensitive subalpine ecosystems of Rocky Mountain National Park (RMNP) in the United States. However, little is known about the local contribution of NH₃ from soils within the park. Thus, the goal of this study was to quantify and compare NH₃ emissions from intact soil cores sampled from a subalpine grassland and forest within RMNP. Cores were collected at 2-wk intervals from 20 June 2011 to 12 Sept. 2011 and transferred to a laboratory chamber system for NH₃ flux measurements. Additionally, N wet deposition was monitored at the sampling location to investigate possible impacts on NH₃ soil emissions. The average quantifiable NH₃ emissions (with SDs) from intact soil cores analyzed in the laboratory (23°C) were 0.42 ± 0.30 mg NH₃–N m⁻² d⁻¹ for grassland soil and 0.21 ± 0.03 mg NH₃–N m⁻² d⁻¹ for forest soil (p < 0.001). A mechanistic model was developed to estimate the impact of temperature on soil emissions using the chamber data and field-site air temperatures. Average estimated NH₃ emissions from the field site over the study period were 0.21 and 0.082 mg NH₃–N m⁻² d⁻¹ for grasslands and forests, respectively. Ammonium wet deposition was not correlated to short term reemission of NH₃ based on N isotope analysis. This work provides new information on the magnitude of NH₃ emissions from native subalpine soils, indicating that natural emissions are not likely major sources of NH₃ in the RMNP airshed.