Assessing the Ability of Nitrogen Isotopes to Distinguish Ammonia Sources Affecting Rocky Mountain National Park

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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 showed that reduced N contributions from within Colorado were 45% and 36% for the spring and summer, respectively.  There is still much uncertainty as to how much each source within Colorado contributes to ammonia deposition in RMNP. The major goal of this study is to determine whether the isotopic signature of nitrogen can be used as a tracer for ammonia released from sources within Colorado into RMNP. Ammonium samplers were deployed in May of 2011.   All samples were collected using passive samplers, Radiellos, deployed for two week and monthly integrations periods. Samples were collected from confined animal feeding operations (beef production), dairies, wastewater reclamation, urban, cropland and RMNP. Sample locations were chosen based its proximity in comparison to RMNP and the availability of meteorological data. The collected ammonia was analyzed using Ion Chromatography, and then diffused onto filters or oxidized for isotopic analysis.  Additionally, soil emission studies (grasslands and forests) and weekly wet deposition were collected at two sites varying in elevation in RMNP.   Results thus far have shown that wet deposition in the park was similar to previous years based on the amount of precipitation and N deposition.  Ammonia isotopic data showed that some sources are significantly different than others, such as wastewater reclamation, dairies, and beef production. However, cropland sources did not significantly differ from dairies and beef production.

Why Study Nitrogen Isotopes?

To assess the potential of isotopes to indicate sources affecting ammonia deposition in Rocky Mountain National Park

What Did We Do?

Gas phase ammonia was measured at sources and in RMNP, as well as, weekly wet deposition was collected in RMNP.   Isotopes were measured on these samplers to compare differences and establish trends.

What Have We Learned?

Some source emissions isotope values can be distinguished, however, mixing and reaction chemistry in the atmosphere diminishes these differences.  The was seen in the measurements in wet deposition.  However, this type of study may be a useful tool to understanding modes of transoport.

Future Plans

Investigations into atmospheric reaction chemistry that can change isotopic values.  Furthermore, single deposition eveny measurements would provide more valuable information on


Joshua Stratton, Ph. D candidate, Colorado State Unversity,

Jay M Ham, Colorado State University, Christina Williams, Colorado State University, Damaris Roosendaal, Colorado State University, Thomas Borch, Colorado State University

Additional Information

(video) Ammonia Deposition in Rocky Mountain National Park : What Is the Role of Animal Agriculture?


Jeff Collette Jr., Katie Benedict

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