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Modeling of Ammonia Dry Deposition to a Pocosin Landscape Downwind of a Large Poultry Facility
Citation:
Walker, Johnt, W. Robarge, AND R. Austin. Modeling of Ammonia Dry Deposition to a Pocosin Landscape Downwind of a Large Poultry Facility. AGRICULTURE, ECOSYSTEMS & ENVIRONMENT. Elsevier Science Ltd, New York, NY, 185(0):161-175, (2014).
Impact/Purpose:
The objective of this study is to estimate NH3 dry deposition to a pocosin landscape downwind of a large poultry facility in the coastal plain region of North Carolina, USA. A semi-empirical modeling approach is used to estimate bi-directional air-surface exchange fluxes of NH3 from measured atmospheric concentrations, meteorological parameters, and the chemical and physical characteristics of the soil/vegetation of the receiving ecosystem. We then examine the magnitude of the NH3 dry deposition fluxes within the context of the total atmospheric deposition budget.
Description:
A semi-empirical bi-directional flux modeling approach is used to estimate NH3 air concentrations and dry deposition fluxes to a portion of the Pocosin Lakes National Wildlife Refuge (PLNWR) downwind of a large poultry facility. Meteorological patterns at PLNWR are such that some portion of the refuge is downwind of the poultry facility 45%, 66%, 57%, and 46% of time during winter, spring, summer, and fall, respectively. Air concentrations and dry deposition rates are highest in the northeasterly direction from the facility, consistent with prevailing wind patterns. Dry deposition rates along the axis of highest concentrations are 10.1 kg N ha-1 yr-1 at the refuge boundary closest to the facility, decreasing to 5.4 kg N ha-1 yr-1 1.5 km further downwind and continuing to decrease non-linearly to a deposition rate of 1.4 kg N ha-1 yr-1 8 - 10 km downwind. Approximately 10% of the refuge model domain receives ≥ 3.0 kg N ha-1 yr-1 as dry NH3 deposition. Depending on the definition of the background air concentration, annual nitrogen loading to the refuge from background NH3 dry deposition and NH3 dry deposition associated with elevated concentrations downwind of the facility is between 41% and 79% higher than background dry NH3 deposition alone. Relative to the total N deposition budget for the refuge, which includes all nitrogen compounds, total background N deposition plus NH3 dry deposition associated with elevated concentrations downwind of the facility is, correspondingly, 6% to 10% greater than background total N deposition alone. From a process standpoint, predicted fluxes are most sensitive to uncertainty in the parameterization of the cuticular resistance.
