Evaluation of National Atmospheric Deposition Program measurements for colocated sites CO89 and CO98 at Rocky Mountain National Park, water years 2010–14

Atmospheric wet-deposition monitoring in Rocky Mountain National Park included precipitation depth and aqueous chemical measurements at colocated National Atmospheric Deposition Program/National Trends Network (NADP/NTN) sites CO89 and CO98 (Loch Vale) during water years 2010–14 (study period). The colocated sites were separated by approximately 6.5 meters horizontally and 0.5 meter in elevation, in accordance with NADP siting criteria. Assessment of the 5-year record of colocated data is intended to inform man-agement decisions pertaining to the achievement of nitrogen deposition reduction goals of the Rocky Mountain National Park Nitrogen Deposition Reduction Plan.

The data at site CO98 met NADP completeness criteria for the first time in 29 years of operation in 2011 and then again in 2012. During the study period, data at site CO89 met completeness criteria in 2012. Median weekly relative precipitation-depth differences between sites CO89 and CO98 ranged from 0 to 0.25 millimeter during the study period. Median weekly absolute percent differences in sample volume ranged from 5 to 10 percent. Median relative concentration differences for weekly ammonium (NH₄⁺) and nitrate (NO₃^-) concentrations were near the NADP Central Analytical Laboratory’s method detection limits and thus were considered small. Absolute percent differences for water-year 2010–14 precipitation-weighted mean concentrations of NH₄⁺, NO₃^-, and inorganic nitrogen (N_inorg) ranged from 0.0 to 25.7 percent. Absolute percent differences for water-year 2010–14 NH₄⁺, NO₃^-, and N_inorg deposition ranged from 2.1 to 18.9 percent, 3.3 to 24.5 percent, and 0.3 to 17.4 percent, respectively.