This book provides an up-to-date synthesis of the understanding of the interaction between the emission of nitrogen, its deposition and impact on the most important components of natural and semi-natural ecosystems. The work consists of contributions from internationally renowned research scientists. Individual chapters deal with the factors and processes related to nitrogen deposition and soils, non-forest vegetation communities, forest ecosystems, and surface waters. The assessment of these impacts is discussed in terms of setting critical loads. The book is aimed at researchers, advanced course students and policy makers/advisors involved with aspects of the impact of air pollution.

In the past century, anthropogenic activities have increased N input drastically to terrestrial ecosystems and influenced the global N cycle. Especially temperate forest ecosystems are affected in their productivity, species composition, soil chemistry and water quality. N input to forest ecosystems is retained in trees and soil. Excessive N is leached out or released as gases. The retention of N input in soils is mainly influenced by the stability of soil organic matter (SOM). Many forests in central Europe and North America have been subjected to N saturation, i.e. excessive N appeared as nitrate in the leachate below the rooting zone. Reduction of atmospheric N emission and consequent atmospheric N deposition is proposed to be the only practical long-term solution to improve N-saturated forest ecosystems. However, responses of N-saturated forest ecosystems to reduced atmospheric N deposition have been seldom investigated. In the present study, atmospheric deposition was manipulated through roof constructions below the canopy of a mature Norway spruce forest on the Solling plateau in central Germany. A £^(5)N tracer field and a density fractionation laboratory experiment were conducted in the present study to investigate the influence of long-term reduced atmospheric N deposition on the partitioning of atmospheric N in different forest ecosystem compartments as well as on the partitioning of atmospheric N retained in the soil in different SOM pools.

Atmospheric Nitrogen Deposition in Global Forests: Spatial Variation, Impacts, and Management Implications provides the most comprehensive knowledge on spatial variation and ecological impacts of reactive nitrogen deposition in global forests, as well as forest management options to mitigate the negative impacts. Written and edited by international experts in the field, this book synthesizes recent research developments and insights in monitoring and modeling nitrogen deposition in global forests. The book also assesses ecological impacts of enhanced nitrogen deposition on forest structure and function and responses of forest ecosystems to decreasing nitrogen deposition in regions such as the European Union and North America. Finally, the book reviews indicators and thresholds for nitrogen saturation in global forests and analyzes remediation options to reduce impacts of excess nitrogen deposition. This is an important resource for researchers in forestry and biodiversity conservation, as well as graduate students, policymakers and others who want to understand environmental issues of reactive nitrogen deposition in global forests. Offers a systematic view of the ecological impacts of enhanced nitrogen deposition Provides the most comprehensive knowledge on spatial variation and the ecological impacts of reactive nitrogen deposition in global forests Presents expert research and findings on forest management options to remediate negative impacts

A critical load (CL) is a science-based threshold that identifies the amount of pollutant deposition below which no significant ecological harm to an ecosystem component is expected. This report provides baseline critical load (CL) analyses for nitrogen (N) and sulfur (S) as required under the 2012 Planning Rule for forest plan assessments. The data also can be used to inform land management decisions where the effects of N and S deposition are relevant, including the evaluation of large projects through the National Environmental Policy Act, Prevention of Significant Deterioration (PSD) permitting program, wilderness monitoring, and watershed condition. Significant portions of the USDA Forest Service system lands in the Intermountain Region are exposed to N deposition levels that exceed CLs. Areas in exceedance have an increased risk of negative ecological effects. Nine of the 12 National Forests within the Intermountain Region have areas that exceed CLs for surface water acidification and therefore are at higher risk for declines in abundance and diversity of aquatic species. All 12 National Forests have areas that exceed CLs for surface water eutrophication, lichen species richness, forage lichen abundance, and tree species growth rate and probability of survival (over 10 years). In areas with increased risk of surface water eutrophication, competitive interactions and community structure of primary producers can shift and cause compounding effects within the food web. Diversity and abundance of key aquatic species may decrease to the point of extirpation. Areas that exceed CLs for lichen species richness and forage lichen abundance have an increased risk to experience reduced diversity, occurrence, and abundance of lichen species which can negatively affect other biota such as mammals, birds, and invertebrates, that rely on lichens for food, shelter, and camouflage. Areas with an increased risk for declines in tree growth rate and probability of survival may experience a change in the composition of forest communities.

Despite effective global-scale legislation to restrict the emissions of nitrogen (N) into the atmosphere, atmospheric deposition of N remains high in many forested regions. In addition, many N-impacted forests still retain the imprint of N saturation, such as altered species composition and leaching of essential base cations. Accordingly, we need a further understanding of the complexities of N cycling in forest ecosystems and the effects of excess N on forest biodiversity and biogeochemical cycling. This volume explores these complexities, including effects on plants, plant assemblages, and forest biogeochemistry, by synthesizing research from Asia, Europe, and North America. Because of the widespread nature of current declines in N deposition, this book ends with a look to the future as N-impacted forests experience a return to lower levels of atmospheric deposition of N.