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. 2018 Dec;243(Pt B):1287-1301.
doi: 10.1016/j.envpol.2018.09.084. Epub 2018 Sep 20.

Spatial variation of modelled total, dry and wet nitrogen deposition to forests at global scale

Donna B Schwede  1 , David Simpson  2 , Jiani Tan  3 , Joshua S Fu  3 , Frank Dentener  4 , Enzai Du  5 , Wim deVries  6
Affiliations

Spatial variation of modelled total, dry and wet nitrogen deposition to forests at global scale

Donna B Schwede et al. Environ Pollut. 2018 Dec.

Abstract

Forests are an important biome that covers about one third of the global land surface and provides important ecosystem services. Since atmospheric deposition of nitrogen (N) can have both beneficial and deleterious effects, it is important to quantify the amount of N deposition to forest ecosystems. Measurements of N deposition to the numerous forest biomes across the globe are scarce, so chemical transport models are often used to provide estimates of atmospheric N inputs to these ecosystems. We provide an overview of approaches used to calculate N deposition in commonly used chemical transport models. The Task Force on Hemispheric Transport of Air Pollution (HTAP2) study intercompared N deposition values from a number of global chemical transport models. Using a multi-model mean calculated from the HTAP2 deposition values, we map N deposition to global forests to examine spatial variations in total, dry and wet deposition. Highest total N deposition occurs in eastern and southern China, Japan, Eastern U.S. and Europe while the highest dry deposition occurs in tropical forests. The European Monitoring and Evaluation Program (EMEP) model predicts grid-average deposition, but also produces deposition by land use type allowing us to compare deposition specifically to forests with the grid-average value. We found that, for this study, differences between the grid-average and forest specific could be as much as a factor of two and up to more than a factor of five in extreme cases. This suggests that consideration should be given to using forest-specific deposition for input to ecosystem assessments such as critical loads determinations.

Keywords: Dry deposition; Forest biomes; Modelling approach; Nitrogen deposition; Wet deposition.

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Figures

Figure 1.
Figure 1.
Global forest coverage (%) in 18.5x18.5 km2 grid cells based on the Globcover data (http://due.esrin.esa.int/page_globcover.php).
Figure 2.
Figure 2.
Multimodel mean total N deposition (kgN ha−1yr−1) from the HTAP2 project on grid cells with a forest cover >5%.
Figure 3.
Figure 3.
Contribution of dry deposition to total deposition at grid level for total N (top), NOy (middle) and NHx (bottom) based on HTAP II multi-model model results.
Figure 4.
Figure 4.
Contribution of NHx deposition to total deposition (top), dry deposition (middle) and wet deposition (bottom) based on the HTAP II multi-model mean results.
Figure 5.
Figure 5.
Ratio of the forest-specific deposition to grid cell average deposition by the EMEP model for total deposition of total N (top), NOy (middle) and NHx (bottom).
Figure 6.
Figure 6.
Ratio of the forest-specific deposition to grid cell average deposition by the EMEP model for dry deposition of total N (top), NOy (middle) and NHx (bottom).
See this image and copyright information in PMC

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