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 the Rocky Mountain National Park (RMNP). The Colorado Department of Public Health and Environment has estimated that 60% of the NH₃ deposition in the 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 important if future regulations require that agriculture be held accountable for NH₃-related ecosystem damage. One way to possibly track N to its original source is via N isotopic signatures (δ¹⁵N) since the ratio between the ¹⁴N and ¹⁵N isotopes is influenced by source.

A major goal of this project is to assess the effectiveness of isotopes as tracers, and in turn to determine sources of NH₃ contributing to N deposition in the RMNP. The original objectives were to 1) determine the major sources of NH₃ deposition in the 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 the RMNP from animal feeding operations, synthetic fertilizers and other sources. Ammonia sampling (radiello) in the RMNP continued in 2012, as did analysis of wet deposition and soil emissions. Also, preliminary studies on urea hydrolysis and experimental development towards investigating Henry’s constant were initiated.

The larger dataset of N isotopes from the radiello study showed that wastewater remediation exhibited a significantly different isotopic value than dairy cattle, beef cattle and crop land. Furthermore, dairy cattle and beef cattle were significantly different, but crop land was not significantly different from either beef or dairy cattle. Hence, contrary to original speculation, this methodology cannot ultimately be used to effectively distinguish between (deposited atmospheric ammonia) N from fertilizer applied to crop land and N from manure. Thus, from this study, it is not possible to make a clear statement regarding the impact of N fertilizer on NH₃ deposition in the RMNP. CO-13