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 (o¹⁵N) 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 NH₃ contributing to N deposition in RMNP. This study seeks to: 1) determine the major sources of NH₃ deposition in RMNP based on N 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.

The first year of this study was spent determining the best approach to isotope analysis. After laboratory methods were established, construction of appropriate equipment was initiated. Progress over the past year includes completion of conditional samplers for field studies, some field sampling, and NH₃ studies from native soils in the RMNP. Field sampling from certain sites has presented difficulties associated with mixing from neighboring sources, thus necessitating the construction of conditional samplers. RMNP native soil studies have shown that NH₃ flux can vary greatly with sampling period. Additionally, grassland soils have higher NH₃ emissions than forest soils. Preliminary analysis of volatilized NH₃ shows that N deposited in RMNP via precipitation is retained by the soil. CO-13F