Nitrogen deposition and its impacts on forest ecosystems
2023
de Vries, Wim | Du, Enzai
Since 1960, anthropogenic activities have doubled the inputs of reactive nitrogen (N) to the biosphere and caused cascading effects on soil, air, and water quality as well as human and ecosystem health. As an important component of global N cycling, N deposition has been greatly increased in comparison to its ambient levels, although it has recently shown a decline in some regions (e.g., EU and US) with the implementation of emission reduction policies. As an external N input, N deposition is found to exert significant impacts on forest ecosystems that cover approximately one third of the global land surface and provide essential ecosystem services. In this overview chapter, we summarize the (i) current monitoring and modeling approaches to understand the spatial variation in N deposition to global forests, (ii) ecological and biogeochemical impacts of enhanced N deposition, (iii) responses of forest ecosystems to declining N deposition mainly in Europe and the Northeastern United States, and (iv) thresholds of N saturation, the estimated critical loads and management options to mitigate the negative impacts of N deposition. Finally we highlight several knowledge gaps that remain in the patterns, effects and managements of N deposition to global forests, which can inspire future research efforts and inform N emission policies.
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