Predicting nitrogen flux along a vertical canopy gradient in a mixed conifer forest stand of the San Bernardino Mountains in California

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Title: Predicting nitrogen flux along a vertical canopy gradient in a mixed conifer forest stand of the San Bernardino Mountains in California

Author: Arbaugh, Michael J.; Bytnerowicz, Andrzej; Fenn, Mark E.

Date: 1998

Source: In: Bytnerowicz, Andrzej; Arbaugh, Michael J.; Schilling, Susan L., tech. coords. Proceedings of the international symposium on air pollution and climate change effects on forest ecosystems. Gen. Tech. Rep. PSW-GTR-166. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 115-122

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Station ID: GTR-PSW-166

Description: A 3-year study of nitrogenous (N) air pollution deposition to ponderosa pine (Pinus ponderosa Dougl. ex. Laws.) seedlings along a mature tree vertical canopy gradient was conducted in the mixed conifer forest of the San Bernardino Mountains of southern California. Concentrations of nitric acid vapor (HNO₃), particulate nitrate (NO₃^-), and ammonium (NH₄⁺) were measured, as well as dry surface deposition of NO₃^- and NH₄⁺. By using this data, along with meteorological information, a series of simple models were developed that predict the vertical gradient of foliage-rinse surface deposition for NO₃^-, NH₄⁺, and total N. Individual models for NO₃^- and NH₄⁺ were calculated by using deposition data, air concentrations at the top of the canopy, and wind speed. These models explained 80 percent of the variation between deposition values at the lower canopy positions. Examination of model coefficients indicated that the two models were not significantly different, and a single model was developed to estimate total N deposition. This model explained less variation than the individual models (R²_N = 0.69) but is a simpler description of the system. All models have two parameters (a₀ and a₁) that are estimated by nonlinear regression. Independent data indicates that the a₁ parameter depends only on the rate of decline in wind speed vertically down the canopy. The a₀ parameter reflects the difference between foliage rinse surface deposition at the top of the canopy and that at lower canopy positions. It indicates that about 20 percent less dry surface deposition occurs at lower canopy positions than expected from wind speed alone for all nitrogenous compounds, most likely because decreased turbulence within the canopy results in increased quasi-laminar boundary layer resistance at lower canopy positions.

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Citation

Arbaugh, Michael J.; Bytnerowicz, Andrzej; Fenn, Mark E. 1998. Predicting nitrogen flux along a vertical canopy gradient in a mixed conifer forest stand of the San Bernardino Mountains in California In: Bytnerowicz, Andrzej; Arbaugh, Michael J.; Schilling, Susan L., tech. coords. Proceedings of the international symposium on air pollution and climate change effects on forest ecosystems. Gen. Tech. Rep. PSW-GTR-166. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 115-122.