Stable nitrogen isotope ratios in wet and dry nitrate deposition collected with an artificial tree

Amounts of dry NO3-N deposition and N isotope ratios in wet and dry NO3-N deposition have been simultaneously determined by examining differences between precipitation collected by open funnels and throughfall collected beneath an artificial Christmas tree. Samples were collected in a forest clearing on Walker Branch Watershed, near Oak Ridge, Tennessee. From mid-summer to early autumn, NO3-N fluxes beneath the artificial tree were always greater than those measured in precipitation indicating the tree's effectiveness as a passive collector of dry NO3-N deposition. Dry NO3-N deposition averaged 60 +/- 9 % of total (wet and dry) deposition. The mean (+/- SD) calculated delta(15)N value for NO3-N in dry deposition was + 5.6 +/- 2.1 degrees/(oo) (n = 6 sampling periods ranging from 4 to 15 days). On averge, this was approximate to 6 degrees/(oo) heavier than measured delta(15)N values for NO3-N in precipitation. The calculated delta(15)N value for NO3-N in dry deposition was consistent with that expected if NOx precursors to HNO3 vapor (the major constituent of dry deposition at this site) originated principally from coal combustion.