N itrogen emissions to the atmosphere due to human activity remain elevated in industrialized regions of the world and are accelerating in many developing regions (Galloway 1995). Although the deposition of sulfur has been reduced over much of the United States and Europe by aggressive environmental protection policies, current nitrogen deposition reduction targets in the US are modest. Nitrogen deposition remains relatively constant in the northeastern United States and is increasing in the Southeast and the West (Fenn et al. in press). The US acid deposition effects

/pdf/nitrogen-saturation-in-temperate-forest-ecosystems-29ixssxci4.pdf

Nitrogen Saturation in Temperate Forest Ecosystems

Most forests in North America remain nitrogen limited, although recent studies have identified forested areas that exhibit symptoms of N excess, analogous to overfertilization of arable land. Nitrogen excess in watersheds is detrimental because of disruptions in plant/soil nutrient relations, increased soil acidification and aluminum mobility, increased emissions of nitrogenous greenhouse gases from soil, reduced methane consumption in soil, decreased water quality, toxic effects on freshwater biota, and eutrophication of coastal marine waters. Elevated nitrate (NO3−) loss to groundwater or surface waters is the primary symptom of N excess. Additional symptoms include increasing N concentrations and higher N:nutrient ratios in foliage (i.e., N:Mg, N:P), foliar accumulation of amino acids or NO3−, and low soil C:N ratios. Recent nitrogen-fertilization studies in New England and Europe provide preliminary evidence that some forests receiving chronic N inputs may decline in productivity and experience greate...

https://www.fs.fed.us/psw/publications/fenn/psw_1998_fenn006.pdf

Nitrogen excess in North American ecosystems: Predisposing factors, ecosystem responses, and management strategies

Abstract Concern is resurfacing in the United States over the long-term effects of excess nitrogen (N) deposition and mobility in the environment. We present here a new synthesis of existing data sets for the northeastern United States, intended to answer a single question: Is N deposition altering the N status of forest ecosystems in this region? Surface water data suggest a significant increase in nitrate losses with N deposition. Soil data show an increase in nitrification with decreasing ratio of soil carbon to nitrogen (C:N) but weaker relationships between N deposition and soil C:N ratio or nitrification. Relationships between foliar chemistry and N deposition are no stronger than with gradients of climate and elevation. The differences in patterns for these three groups of indicators are explained by the degree of spatial and temporal integration represented by each sample type. The surface water data integrate more effectively over space than the foliar or soil data and therefore allow a more comprehensive view of N saturation. We conclude from these data that N deposition is altering N status in northeastern forests.

Is Nitrogen Deposition Altering the Nitrogen Status of Northeastern Forests

The sources and distribution of anthropogenic nitrogen (N), including N fertilization and N fixed during fossil-fuel combustion, are rapidly becoming globally distributed. Responses of terrestrial ecosystems to anthropogenic N inputs are likely to vary geographically. In the temperate zone, long-term N inputs can lead to increases in plant growth and also can result in over-enrichment with N, eventually leading to increased losses of N via solution leaching and trace-gas emissions, and in some cases, to changes in species composition and to ecosystem decline. However, not all ecosystems respond to N deposition similarly; their response depends on factors such as successional state, ecosystem type, N demand or retention capacity, land-use history, soils, topography, climate, and the rate, timing, and type of N deposition. We point to some of the conditions under which anthropogenic impacts can be significant, some of the factors that control variations in response, and some areas where uncertainty is large due to limited information.

The globalization of nitrogen deposition: consequences for terrestrial ecosystems.

Concern is resurfacing in the United States over the long-term effects of excess nitrogen (N) deposition and mobility in the environment We present here a new synthesis of existing data sets for the northeastern United States, intended to answer a single question: Is N deposition altering the N status of forest ecosystems in this region? Surface water data suggest a significant increase in nitrate losses with N deposition Soil data show an increase in nitrification with decreasing ratio of soil carbon to nitrogen (C:N) but weaker relationships between N deposition and soil C:N ratio or nitrification Relationships between foliar chemistry and N deposition are no stronger than with gradients of climate and elevation The differences in patterns for these three groups of indicators are explained by the degree of spatial and temporal integration represented by each sample type The surface water data integrate more effectively over space than the foliar or soil data and therefore allow a more comprehensive view of N saturation We conclude from these data that N deposition is altering N status in northeastern forests

https://udel.edu/~inamdar/nps2007/n_discussion.pdf

https://www.srs.fs.usda.gov/pubs/ja/ja_mcnulty002.pdf

Steven D. Newman

Papers

Nitrogen saturation in a high elevation New England spruce-fir stand☆