2022 monitoring and tracking wet nitrogen deposition at Rocky Mountain National Park: May 2024

Abstract

The Colorado Department of Public Health and Environment (CDPHE), the National Park Service (NPS), and the U.S. Environmental Protection Agency (EPA) issued the Nitrogen Deposition Reduction Plan (NDRP) in 2007 to address the impacts of nitrogen deposition at Rocky Mountain National Park (RMNP). The agencies chose a glidepath approach to reduce wet nitrogen deposition to a level of 1.5 kilograms of nitrogen per hectare per year (kg N/ha/yr), the resource management goal, by the year 2032 to protect sensitive ecosystems within RMNP. This report summarizes wet nitrogen deposition data collected in 2022 and places it in the context of measurements made since 1984. In 2022, wet nitrogen deposition (5-year average) at Loch Vale in RMNP was 2.8?0.22 kg N/ha/yr, which is above the glidepath (2.2 kg N/ha/yr), but below the 2006 baseline of 3.3 kg N/ha/yr. Another goal of the NDRP is to ?reverse the trend of increasing nitrogen deposition at the park? that occurred from 1984 to 2000. Trends in wet nitrogen deposition, ammonium and nitrate concentrations, and precipitation were analyzed at three sites in RMNP and four regional sites outside of the park. Wet nitrogen deposition has not decreased at any of the RMNP locations or other sites in the region over the long-term (>35 years). Moreover, wet nitrogen deposition and precipitation increased at the Beaver Meadows site in RMNP. Ammonium concentrations showed a statistically significant increase at three of four sites and nitrate concentrations showed a significant decrease at four sites over the period of record (p-value?0.05). Since the NDRP was developed in 2006, wet nitrogen deposition showed no significant trend at sites in RMNP, but significantly decreased at one regional site, Pawnee. Concentrations of ammonium showed no trends and concentrations of nitrate significantly decreased from 2006-2022 at all four sites that met data completion criteria. Even though the trend in wet nitrogen deposition did not decrease significantly at Loch Vale since 2006, the current wet nitrogen deposition (2018-2022) of 2.8 kg/ha/yr is approximately 15% lower than the baseline average (2002-2006) of 3.3 kg/ha/yr. Wet nitrogen deposition at Loch Vale has decreased 0.5 ? 0.38 kg/ha/yr (0.13 to 0.88 kg/ha/yr) at the 95% confidence interval, suggesting some progress has been made.