Nitrogen deposition in and around an intensive agricultural district in central New York

Emissions of NH₃ from intensive agriculture may perturb natural ecosystems by increasing atmospheric N deposition. This study was undertaken to quantify patterns of atmospheric chemistry and N deposition in and around a highly intensive agricultural district and thereby to improve understanding of the fate of NH₃ emissions and possible effects on regional forests. Atmospheric chemistry, wet and bulk deposition, canopy throughfall, and soil and vegetation N status were measured at a suite of sites in and around the agricultural district centered in southern Cayuga County, New York. Concentrations of NH₄/⁺ and acidic gases and particulates were slightly elevated compared with regional background values. Temporal variations in these species were consistent throughout the district and surrounding areas, suggesting wide dispersion. In contrast, NH₃ concentrations were greatly elevated within the district (often >1 μg m^-3), comparable to values in southeastern Netherlands, but declined to moderate values in outlying areas (0.2 μg m^-3). Bulk deposition of NH₄⁺ near large farms (7-8 kg NH₄-N ha^-1 yr^-1) was over twice as high as the regional background, declining to levels about 50% above background throughout the district but more than 2 km away from large farms (4-5 kg NH₄-N ha^-1 yr^-1). These values must be regarded as tentative estimates because of probable high seasonal and annual variation and the limited intervals of sampling in the current study. Also, gaseous deposition of NH₃ to forests in the district probably contributes significantly to total deposition, but its magnitude remains uncertain.