Dry deposition of nitrate to a deciduous forest |
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Authors: | Gary M. Lovett Steven E. Lindberg |
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Affiliation: | (1) Institute of Ecosystem Studies, The New York Botanical Garden, The Mary Flager Cary Arboretum, Box AB, Milbrook, New York 12545, USA;(2) Environmental Sciences Division, Oak Ridge National Laboratory, 37831 Oak Ridge, Tennessee, USA |
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Abstract: | Because dry-deposition inputs are difficult to measure, they are often ignored in biogeochemical studies. In this study three separate methods were used to estimate dry deposition of nitrate to a deciduous forest (Walker Branch Watershed) in eastern Tennessee. The range of estimates of dry-deposition flux was from 1.8 to 9.1 kg NO3--N ha-1 yr-1 Using a hybrid approach that combines some aspects of all three methods, a best estimate of 4.8 kg NO3--N ha-1 yr-1 was derived. About 75% of this flux is attributable to deposition of HNO3, vapor with large particles contributing most of the remainder; the contribution from small particles is negligible. The range of estimates obtained from the three techniques suggest that dry-deposition measurements should be interpreted with caution.Our best estimate indicates that dry deposition of NO3- is the largest single form of inorganic nitrogen (N) deposition to this forest, contributing almost half of the 10.1 kg N ha-1 total annual input. All of the enhancement of NO3- deposition in stemflow and throughfall relative to incident precipitation can be explained by washoff of dry-deposited NO3-, and some canopy uptake of dry-deposited NO3- is suggested. This uptake occurs primarily during the growing season and contributes from 0.2 to 7.5 kg N ha-1 yr-1 to the N requirements of the ecosystem, with a best estimate of 3.2. Despite the uncertainties, the magnitude of the potential input fluxes to forested ecosystems necessitates consideration of nitrate dry deposition in ecosystem nitrogen cycling studies. |
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Keywords: | Nitrogen atmospheric deposition throughfall stemflow nitric acid vapor |
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