8.04.06 - Nitrogen and sulfur deposition
Excess input of nitrogen and sulfur is harmful for forest health and functions of the ecosystems. The 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 WPs in the RG 8.04, in particular to:
- WP 8.04.01: Detection and monitoring
- WP 8.04.03: Atmospheric deposition, soils and nutrient cycles
- WP 8.04.04: Modelling and risk assessment
- WP 8.04.08: Multiple stressors
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). Although NOX emissions from anthropogenic sources have already started declining in many regions, including Northeast Asia, NH3 emissions have not been enough reduced. Therefore, nitrogen deposition and its effects on forest ecosystems should still be investigated for a while.
Sulfur emissions have already enough been reduced in Europe and North America. Those in other regions, including Northeast Asia, have also started declining. Recovery process from acidification and dynamics of sulfur under climate change 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; Sase et al. 2019, Biogeochemistry). With reduction of SO2 (and probably NOX) emissions, atmospheric reactions of Nr are changing (e.g. gaseous NH3 may not effectively be transformed to particulate matters). To understand Nr behaviors precisely, sulfur deposition should also be monitored.
Investigation on interactions with other stressors, including air pollutants and climate change, has become more important to understand forest ecosystems. Respective roles of multiple stressors for forest ecosystems are large knowledge gaps. Cooperation with other WPs is very important to fill the gaps.