Inicio Eventos - Instituto de Ciencias de la Atmósfera y Cambio Climático Atmospheric deposition of reactive nitrogen to a southern Appalachian deciduous forest

Atmospheric deposition of reactive nitrogen to a southern Appalachian deciduous forest

Viernes 09 de abril de 2021 – 12:00 PM

IMPARTE: Dr. John T. Walker┃U.S. Environmental Protection Agency’s Office of Research and Development, Center for Environmental Measurement and Modeling.

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ABSTRACT

Assessment of critical load exceedances for nutrients requires complete and accurate atmospheric deposition budgets for reactive nitrogen (Nr). The exceedance is the total amount of Nr deposited to the ecosystem in excess of the critical load, which is the amount of Nr input below which harmful effects do not occur. Total deposition includes all forms of Nr (i.e., organic and inorganic) deposited to the ecosystem by wet and dry pathways.  Total deposition budgets are often incomplete due to lack of consideration of organic forms of Nr and uncertain due to reliance on models for estimating the dry deposited fraction.  Here we present results from the Southern Appalachian Nitrogen Deposition Study (SANDS) in which a combination of measurements and field-scale modeling is used to develop a complete annual (2015) Nr deposition budget for a mixed deciduous forest at the Coweeta Hydrologic Laboratory in southern Appalachia.  Wet deposition of ammonium, nitrate, nitrite, and bulk organic N were measured directly.  The dry deposited Nr fraction was estimated using a bidirectional resistance-based model driven with speciated measurements of Nr air concentrations (e.g., ammonia, ammonium aerosol, nitric acid, nitrate aerosol, bulk organic N in aerosol, total alkyl nitrates, and total peroxy nitrates), micrometeorology, canopy structure, and biogeochemistry.  Wet deposition contributed 58% of total annual deposition.  Approximately 53% of the total (wet + dry) budget was contributed by reduced forms of Nr (NHx = ammonia + ammonium), with oxidized and organic forms of Nr contributing ~ 40% and 7%, respectively. The dry deposited fraction comprised ~ 60% NHx, with oxidized and organic Nr contributing ~ 35% and 5%, respectively.  Total annual deposition was ~ 7.0 kg N ha-1 yr-1, which is on the upper end of Nr critical load estimates recently developed for similar ecosystems in nearby Great Smoky Mountains National Park.  Our results indicate that reductions in NHx deposition would be needed to achieve the lowest estimates (~ 3.0 kg N ha-1 yr-1) of Nr critical loads in southern Appalachian forests.

 

Dr. John T. Walker

Is a Senior Research Physical Scientist in the U.S. Environmental Protection Agency’s Office of Research and Development, Center for Environmental Measurement and Modeling.  Dr. Walker’s research investigates atmosphere-biosphere exchange of reactive and radiatively important trace gases and particulate matter in natural and agricultural landscapes.  Dr. Walker and his research team conduct field and laboratory experiments to improve emission inventories for gases such as ammonia, nitrous oxide, and methane from biogenic and agricultural sources, improve atmospheric deposition budgets for reactive nitrogen compounds, and improve air-surface exchange algorithms in chemical transport models.  Much of Dr. Walker’s work at EPA has focused on better understanding the processes by which ammonia is exchanged between the atmosphere and ecosystems and its contribution to reactive nitrogen deposition.  Dr. Walker received B.S. and M.S. degrees in Atmospheric Science and a Ph.D. in Soil Science from North Carolina State University.  He is an Adjunct Associate Professor in the Department of Marine, Earth and Atmospheric Sciences at North Carolina State University and is currently vice chair of the Executive Committee of the U.S. National Atmospheric Deposition Program. 

 

Fecha

Abr 09 2021
Finalizdo!

Hora

12:00 pm - 1:00 pm

Etiquetas

Seminario Institucional