Ammonia Emissions from Subalpine Forest and Mountain Grassland Soils in Rocky Mountain National Park

Abstract

Atmospheric deposition of NH and NH contributes to eutrophication within sensitive subalpine ecosystems of Rocky Mountain National Park (RMNP) in the United States. However, little is known about the local contribution of NH from soils within the park. Thus, the goal of this study was to quantify and compare NH emissions from intact soil cores sampled from a subalpine grassland and forest within RMNP. Cores were collected at 2-wk intervals from 20 June 2011 to 12 Sept. 2011 and transferred to a laboratory chamber system for NH flux measurements. Additionally, N wet deposition was monitored at the sampling location to investigate possible impacts on NH soil emissions. The average quantifiable NH emissions (with SDs) from intact soil cores analyzed in the laboratory (23°C) were 0.42 ± 0.30 mg NH-N m d for grassland soil and 0.21 ± 0.03 mg NH-N m d for forest soil ( < 0.001). A mechanistic model was developed to estimate the impact of temperature on soil emissions using the chamber data and field-site air temperatures. Average estimated NH emissions from the field site over the study period were 0.21 and 0.082 mg NH-N m d for grasslands and forests, respectively. Ammonium wet deposition was not correlated to short term reemission of NH based on N isotope analysis. This work provides new information on the magnitude of NH emissions from native subalpine soils, indicating that natural emissions are not likely major sources of NH in the RMNP airshed.

Ammonia Dry Deposition in an Alpine Ecosystem Traced to Agricultural Emission Hotpots

“…forest. 33 The EC measurements were conducted from July to August in 2015 and from June to August in 2016. Soil NH 3 emissions from the grassland and the forest areas have been measured with detailed soil information.…”

“…Soil NH 3 emissions from the grassland and the forest areas have been measured with detailed soil information. 33 N r deposition at the site has been measured annually (3.65 kg N ha −1 yr −1 in 2009), which includes wet N deposition and dry deposition estimates of nitric acid (HNO 3 ), NH 3 , particulate ammonium (NH 4 + ), and particulate nitrate. Dry NH 3 deposition was estimated by multiplying NH 3 concentrations by scaled HNO 3 deposition velocity.…”

Summertime Soil-Atmosphere Ammonia Exchange in the Colorado Rocky Mountain Front Range Pine Forest

“…This assumes all extracted [NH 4 + ] represents the amount found in soil pore water that can volatilize into the atmosphere. Recent chamber studies of soil, either of core samples [15] or overtop the intact soil [38,39], overcome this limitation by measuring the NH 3 emission directly. However, enclosure experiments, such as chambers, have difficulty in recreating the turbulent mixing that regulates the transfer velocity between the soil and atmosphere under ambient conditions, which is critical for fluxes that are driven by a compensation point, such as for NH 3 .…”

“…The correlation they observed with air temperature led to the assumption the plant canopy was solely responsible for increased NH 3 concentrations in the NH 3 -poor air. More than two decades later, a study examined the soil contribution of NH 3 emissions to the atmosphere within the Colorado Front Range [15]. Based on chamber measurements of extracted soil cores, Stratton et al reported an average emission flux of 0.21 ± 0.03 mg NH 3 -N m −2 d −1 .…”

“…As a result, the magnitude, and even sign, of net NH 3 exchange are challenging to predict. Many reports, including Stratton et al, use compensation point (χ) modeling to predict the magnitude and direction of NH 3 exchange (i.e., flux) [15,[18][19][20][21][22][23]. Due to the technical and instrumental demands of measuring fluxes directly (i.e., through eddy covariance), compensation point modeling offers an affordable alternative to infer fluxes.…”