The Impacts of Increasing Atmospheric Nitrogen Deposition on Forest Carbon Accumulation in the U.S. Mid-Atlantic Region
Abstract
The global carbon assessments have suggested that the mid-latitude forests are likely the primary places where carbon sequestration has been enhanced because of increasing anthropogenic N deposition. In this paper, we examine the idea with a regional study of the U.S. mid-Atlantic and present the estimate produced by a dynamic and process-based forest ecosystem model, PnET-CN. For the U.S. mid-Atlantic region, forests cover about 56% of the total land area. The pattern of N deposition varies across the region because of complicated landscape features and land-use types. High wet deposition generally occurs in the northern lake and high elevation areas, as well as urban/suburban especially metropolitan areas. The N deposition data used for the modeling were from the 1999 scenario that was generated by a research group at Penn State University using interpolation algorithms based on concentration data collected at National Atmospheric Deposition Project/ National Trends Network monitoring sites and precipitation data from a denser network of National Atmospheric and Oceanic Administration Cooperative climatic sampling sites. We assumed that N deposition in 1930 was about 25% of the 1999 level and interpolated this level linearly back to 1930 for each 1-km square pixel within the region. Our simulations based on the ramped N increase and controlled N level in the past 70 years indicate that the growth effect of a sustained increase of N deposition could vary in different locations and forest types. For example, some mountain coniferous forests are likely N saturated and the increased N deposition had little effect on forest growth. Deciduous forests in the region seemed to respond more positively to N deposition. The annual growth rate could be up to 4.7% higher after a long-term exposure to additional N inputs. It is unclear what is the threshold in which additional nitrogen may degrade forest ecosystem function in terms of reducing net photosynthesis, N use efficiency and forest growth. The results reported here are only preliminary because (1) we only simulated the growth impacts from additional wet N deposition due to the lack of dry deposition data, and (2) the assumption of a ramped increase of N deposition may fail to count the growth effect of inter-annual variations of N deposition that can change tremendously in wet and dry years. The modeling results will be improved along with our on-going research and new data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.B51B0212P
- Keywords:
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- 0400 BIOGEOSCIENCES