Lovett, G.M. and S.E. Lindberg. 1993. Atmospheric deposition and canopy interactions of nitrogen in forests. Canadian Journal of Forest Research, 23(8):1603-1616.

Abstract: Wet deposition of nitrogen compounds was measured and dry and cloud water deposition were estimated at 11 forested sites in North America and one site in Europe. Dry deposition was a significant pathway of N input to all the forests, averaging 46% of the total deposition. At most of these sites, NH4+ was the dominant form of fixed N in the air, but HNO3 vapor dominated the dry deposition of N. Coarse-particle deposition was often important, but fine-particle deposition usually contributed only a small amount of the dry-deposited N. The deposition rates of inorganic N, which ranged between 4.8 and 27 kg N.ha-1.year-1, were generally much higher than has been reported by other studies measuring only wet or bulk deposition. The highest deposition rates were at the high- elevation sites in the southeastern and northeastern United States and much of the deposition at these sites was attributed to cloud water. Throughfall and stemflow (TF + SF) flux was also measured at all sites, and the net canopy exchange (NCE = (TF + SF) - total deposition) was found to be negative (indicated consumption of N in the canopy) for NH4+ and NO3-, and positive (indicating canopy release) for organic N. Past reports of canopy release of NO3- can probably be attributed to washoff of dry-deposited NO3- species. Consumption of inorganic N in the canopy ranged from 1 to 12 kg N.ha-1.year-1, and was highest in the spruce and spruce-fir stands. When organic N was included in the canopy N balance, the net canopy uptake of N was generally <15% of the total system N requirement. Total N deposition was a linear function of wet deposition for low-elevation sites, and dry deposition was a linear function of the net throughfall flux for NO3-.