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Modeling bi-directional fluxes of NH3 in a forest ecosystem using SURFATM-NH3 model: A study with a dataset from a deciduous montane forest in the southeastern U.S.
Citation:
Lichiheb, N., E. Personne, J. Walker, R. Saylor, Z. Wu, X. Chen, D. Schwede, AND C. Oishi. Modeling bi-directional fluxes of NH3 in a forest ecosystem using SURFATM-NH3 model: A study with a dataset from a deciduous montane forest in the southeastern U.S. American Meteorological Society, Phoenix,AZ, January 06 - 11, 2019.
Impact/Purpose:
As NOx emissions continue to decline, it is becoming more important to understand the spatial and temporal patterns of NHx (NH3 + NH4+) deposition, its contribution to total reactive nitrogen deposition budgets, and the processes by which reduced N deposits to ecosystems. Dry deposition of NH3 contributes a large fraction of nitrogen deposition to many ecosystems, yet the magnitude and dynamics of NH3 deposition remain difficult to characterize. Improved bi-directional exchange models are needed to properly simulate net canopy-scale fluxes in natural landscapes, particularly forests, and to partition fluxes to ecosystem compartments.
Description:
Ammonia (NH3) is the most abundant alkaline component in the atmosphere, is therefore of great importance in the neutralization of atmospheric acids and formation of aerosol particles. Numerous studies have been published investigating the effects of NH3 fluxes on agricultural ecosystems since emissions of atmospheric NH3 are mainly related to agriculture. However, NH3 emissions also occur from natural sources and may affect sensitive ecosystems such as forests. Understanding and prediction the biosphere-atmosphere interactions of NH3 in a forest canopy is challenging due to the complex nature of this ecosystem. A two-layer NH3 compensation point model SURFATM-NH3 is used to investigate the NH3 flux partitioning between the ground layer, cuticle and stomata compartments for a deciduous forest ecosystem. As key parameters the model uses an energy budget model that makes possible to simulate surface temperature for which volatilization is very sensitive, as well as measured and estimated soil and stomatal emission potentials. The model simulates the energy balance, surface temperature and NH3 fluxes. Modeling results are evaluated with a data set obtained from a field study carried out in a forest canopy at the U. S. Forest Service’s Coweeta Hydrologic Laboratory in southwestern North Carolina during the summer of 2015. The comparison of modeled and measured results will be presented and the sources of NH3 will be examined, giving propositions for future models improvements.