Contribution of Animal Feeding Operations and Synthetic Fertilizers to Ammonia Deposition in Rocky Mountain National Park

Ammonia (NH₃) deposition has been identified as a concern from both human health and environmental standpoints, and has recently been targeted by Colorado as a primary contributor to atmospheric and ecosystem changes in Rocky Mountain National Park (RMNP). The Colorado Department of Public Health and Environment has estimated that 60% of the NH₃ deposition in RMNP comes from agricultural activities with 40% from animal feeding operations and 20% from fertilizer. However, these estimates have not been verified by scientific measurement, and verification is especially important if future regulations require that agriculture be held accountable for NH₃-related ecosystem damage.

One promising way to track N to its original source is via N isotopic signatures (ä¹⁵N) since the ratio between the ¹⁴N and ¹⁵N isotopes is influenced by source. A major goal of this project is to assess the ability of isotopes as tracers, and in turn to determine sources of ammonia contributing to N deposition in RMNP. The original objectives of this study were to 1) determine the major sources of NH₃ deposition in RMNP based on nitrogen isotopic signatures of different NH₃ sources (i.e., agricultural, natural, and industrial), and 2). quantify the relative contribution of NH₃ to RMNP from animal feeding operations, synthetic fertilizers, and other sources.

Progress over the past year includes completion of an ammonia field sampling (radiellos) campaign, collection of wet deposition in RMNP, and a RMNP soil emission study. Radiellos were placed at seven sites including animal husbandry, urbanized sources, cropland, foothills, and RMNP. Animal husbandry had the highest average ammonia concentrations, ranging from 4x to 100x higher than other sources. Preliminary analysis of nitrogen isotopes has shown some variation across studied sources. Wet deposition is similar to previous studies with 1.39 and 2.00 kg N ha^-1 during the spring and summer, respectively. Ammonia contributed 50% and 30% to total N during the spring and summer period, respectively. Our findings from the RMNP show that grassland soils have higher ammonia emissions than forest soils. Support for this work will continue in 2012. CO-13F.