7.01.10 - Nitrogen and sulfur deposition


Hiroyuki Sase, Japan


Steven McNulty, United States

About Unit

Excess input of nitrogen and sulfur is harmful for forest health and functions of the ecosystems. The new Working Party (WP) studies nitrogen and sulfur deposition with the following objectives:

  • To compile the monitoring data of nitrogen and sulfur deposition in forest area as the global scale
  • To study possible effects of nitrogen and sulfur deposition on biogeochemical processes and biodiversity in forest ecosystems under the climate change
  • To assess capacity of the ecosystems for deposition of nitrogen and sulfur, using indices, such as critical loads.

The objectives above may link to other existing WPs in the RG 7.01, in particular to:

  • WP 7.01.01: Detection and monitoring
  • WP 7.01.03: Atmospheric deposition, soils and nutrient cycles
  • WP 7.01.05: Modelling and risk assessment
  • WP 7.01.08: Hydroecology

State of Knowledge

Nitrogen and sulfur deposition has been discussed in context of acid deposition (so-called 'acid rain'). Although the 'acid rain' issue has been marginalized recently, inputs of nitrogen and sulfur compounds from the atmosphere should be taken into account as the indispensable factors in forest ecosystems. 

Various sources, including fossil fuel combustion, agricultural fields, and livestock, contribute to emissions of reactive nitrogen (Nr) compounds, and therefore, it is difficult to control Nr emissions effectively. Excess input of nitrogen to forest affects its nutrient cycles and may cause eutrophication or nitrogen saturation of the ecosystems (e.g. Aber et al. 1998, Bioscience). Nitrogen deposition itself is also important for biodiversity of indicator species, such as mosses and lichens (e.g. Giordani et al. 2013, Forest Ecology and Management). Effects of nitrogen deposition on nutrient cycles and biodiversity should be studied in forest ecosystems under the climate change.

Sulfur emission has already enough been reduced in Europe and North America. However, recovery process from acidification and dynamics of sulfur should carefully be monitored in watershed scale even in the regions above (e.g. Mitchell et al. 2011 Biogeochemistry; Vuorenmaa et al. 2017, Ecological Indicators). Sulfur emission and its deposition are still high in other regions, such as Asia. It is important in such regions to study not only ongoing acidification but also possible recovery from acidification in the near future. In particular, a large knowledge gap exists in tropical forest, where sulfur deposition is dynamically changing (e.g. Sase et al. 2017, Hydrological Processes).

The data on nitrogen and sulfur deposition in forest area has not been enough compiled in the global scale, especially for contribution of dry deposition. This is also a large gap to be filled for assessment of forest health.