Quantifying Ammonia Emissions from High Elevation Grassland and Forest Soils

Extensive evidence has shown that Rocky Mountain National Park (RMNP) has undergone ecosystem changes due to excessive nitrogen (N) deposition. Previously, the Rocky Mountain Atmospheric Nitrogen and Sulfur (RoMANS) study was conducted to identify the species of N that deposit in RMNP. Results from the RoMANS study were used to identify contributions to N deposition in RMNP showing that local sources provided 33% of the wet-deposited ammonia in RMNP during the summer period. With the uncertainty of the type of local sources and their influence on the N in RMNP, the major goal of this study is to determine the amount of ammonia released from native grassland and forest soils. Intact soil cores were collected from native grassland and forest soils near RMNP on June 28th, July 20th, and August 9th 2010 and monitored in a laboratory chamber study for seven days. The samples were collected in the morning of the sampling dates to limit artifacts such as temperature variations. Ammonia gas released from the cores was collected in an acid trap and analyzed using Ion Chromatography. Results showed that ammonia gas released, based on an average (n = 18) over seven days, was 1.71 and 0.677 mg NH3/m2 soil/day for grassland and forest soils, respectively. Not all of the 36 soil cores investigated lost quantifiable amounts of ammonia. The results are small in comparison to other non-local sources (e.g. animal feeding operations, fertilizer, etc.), but further studies need to be conducted to determine its significance as a local source. Seasonal trends were visible with June 28th being higher than both July 20th and August 9th sampling. Grassland soil emissions were higher than forest soils emissions for all three sampling dates, and water loss from the soil cores did not strongly correlate with ammonia emission. Studies are also being conducted to understand the fate of wet-deposited N on native grassland and forest soils.