Atmospheric Deposition and Critical Loads for Nitrogen and Metals in Arctic Alaska: Review and Current Status

Abstract

To protect important resources under their bureau's purview, the United States National Park Service's (NPS) Arctic Network (ARCN) has developed a series of "vital signs" that are to be periodically monitored. One of these vital signs focuses on wet and dry deposition of atmospheric chemicals and further, the establishment of critical load (CL) values (thresholds for ecological effects based on cumulative depositional loadings) for nitrogen (N), sulfur, and metals. As part of the ARCN terrestrial monitoring programs, samples of the feather moss Hylocomium splendens are being collected and analyzed as a cost-effective means to monitor atmospheric pollutant deposition in this region. Ultimately, moss data combined with refined CL values might be used to help guide future regulation of atmospheric contaminant sources potentially impacting Arctic Alaska. But first, additional long-term studies are needed to determine patterns of contaminant deposition as measured by moss biomonitors and to quantify ecosystem responses at particular loadings/ ranges of contaminants within Arctic Alaska. Herein we briefly summarize 1) current regulatory guidance related to CL values 2) derivation of CL models for N and metals, 3) use of mosses as biomonitors of atmospheric deposition and loadings, 4) preliminary analysis of vulnerabilities and risks associated with CL estimates for N, 5) preliminary analysis of existing data for characterization of CL values for N for interior Alaska and 6) implications for managers and future research needs.

Modeling long‐term changes in tundra carbon balance following wildfire, climate change, and potential nutrient addition

“…To cover a wide range of uncertainties in N deposition estimated from empirical data and global-scale overview (Jaffe and Zukowski 1993, Woodin 1997, Galloway et al 2008, Linder et al 2013) and test the influence of different N deposition rates, we linearly increased annual N deposition rate so that in the 200th year N input was 1, 2, 5, 10, and 20 times the value in 2008 (0.035 g N·m −2 ·yr −1 ), with P weathering rate (1.28 × 10 −4 g P·m −2 ·yr −1 in 2008) increased by the same proportions. To cover a wide range of uncertainties in N deposition estimated from empirical data and global-scale overview (Jaffe and Zukowski 1993, Woodin 1997, Galloway et al 2008, Linder et al 2013) and test the influence of different N deposition rates, we linearly increased annual N deposition rate so that in the 200th year N input was 1, 2, 5, 10, and 20 times the value in 2008 (0.035 g N·m −2 ·yr −1 ), with P weathering rate (1.28 × 10 −4 g P·m −2 ·yr −1 in 2008) increased by the same proportions.…”

“…Only limited information is available on deposition of atmospheric N for the North Slope of Alaska. To cover a wide range of uncertainties in N deposition estimated from empirical data and global-scale overview (Jaffe and Zukowski 1993, Woodin 1997, Galloway et al 2008, Linder et al 2013) and test the influence of different N deposition rates, we linearly increased annual N deposition rate so that in the 200th year N input was 1, 2, 5, 10, and 20 times the value in 2008 (0.035 g N·m −2 ·yr −1 ), with P weathering rate (1.28 × 10 −4 g P·m −2 ·yr −1 in 2008) increased by the same proportions. However, even at these rates, external nutrient supply was very small relative to plant requirements.…”

Assessing the impact of shipping emissions on air pollution in the Canadian Arctic and northern regions: current and future modelled scenarios

“…shipping contributions to the total deposition of S to the three land cover types are small (below 1%), while the contributions to dry deposition (which is more heavily tied to ambient concentrations) are noticeably greater. As shown in Table 9 , which is also below the critical load for acidification 5 currently estimated for the region in Forsius et al (2010) and the empirical critical loads for nutrient N of 1 -3 kg of N ha -1 a -1 for North America ecoregion of tundra (Linder et al, 2013;Pardo et al, 2011).…”

“…It should be noted that, although the current deposition of S and N over the Arctic region are low and generally below the existing critical load estimates, with the 10 projected increase in global production of nitrogen expected to be needed to meet the growing demand for food and energy, atmospheric emissions and depositions of nitrogen are expected to increase (Galloway et al, 2004;Dentener et al, 2006); this situation combined with the expected increase in shipping activities in Arctic waters could raise the level of deposition to above the critical loads for the region. Furthermore, it is recognized that the current estimates of critical loads for North American Arctic ecosystems are highly uncertain due to a number of factors including limitations in methodology and lack 15 of data (Forsius et al, 2010;Pardo et al, 2011;Linder et al, 2013). Given these considerations, a careful assessment of potential ecosystem impacts from Arctic shipping emissions, particularly in the future context, is warranted.…”

Non-Destructive Lichen Biomass Estimation in Northwestern Alaska: A Comparison of Methods

“…Improved burn severity geospatial layers and historic fire perimeters would increase the resolution of these layers by allowing for the modeling of successional status, and hence lichen height and cover. Lichen winter range for the Western Arctic Caribou Herd is projected to suffer some decline with climate-driven shrub increase [1], [35], more frequent wildfire [36], and increasing inputs of nitrogen and sulfur from regional development [38]. Continued monitoring of lichen biomass will be critical for detecting and addressing ongoing changes.…”