Dry deposition determinations, along with wet deposition and throughfall (TF) measurements, at a spruce fir forest in central Maine were used to estimate the effect of atmospherically deposited nitrogen (N) uptake on forest carbon storage. Using nitric acid and particulate N as well as TF ammonium and nitrate data, the growing season (May-October) net canopy uptake of atmospheric, predominantly anthropogenic, N deposition was found to be 1-5 kg N ha-1. The ratio of growing season net canopy N uptake to that of recycled root N uptake (10-30 kg N ha-1, during the growing season) suggests a substantial modification of the N cycle at this Maine spruce fir forest over the past decade. The growing season 1-5 kg ha-1 canopy N uptake may induce an enhanced annual carbon (C) storage of 250-1350 kg C ha-1 yr-1. This magmtude of N-stimulated C storage may be compared with measured annual C sequestration of ~2000 kg C ha-1 for each of the years 1996-1998 at this Maine site. Consideration of four other eastern U.S. forest sites for which net canopy N uptake data are available suggests that from 285 to 2950 kg C ha-1, annual C sequestration may be occurring at these conifer sites, consistent with the Maine site results.
Sievering, Herman; Fernandez, Ivan; Lee, John; Hom, John; Rustad, Lindsey. 2000. Forest canopy uptake of atmospheric nitrogen deposition at eastern U.S. conifer sites: Carbon storage implications? Global Biogeochemical Cycles. 14(4): 1153-1159. https://doi.org/10.1029/2000GB001250.