Document: HER-3-99-148

Atmospheric nitrogen loading at a Rocky Mountain conifer forest: Perturbation of the natural nitrogen cycle and potential carbon storage enhancement.

SIEVERING, H.S.* 1, T.KELLY 1, G.MCCONVILLE 1 and A.TURNIPSEED 2

University of Colorado, Denver, CO 80217 USA 1
University of Colorado, Boulder, CO 80303 USA 2

Abstract:
Dry deposition of gaseous nitric acid (HNO3) at a 3000m subalpine spruce, fir, and pine forest site on Niwot Ridge was measured during the growing season of 1999. The dry deposition velocity for HNO3 was found to be quite large, 5 to 9 cm s-1 (90% CI), indicating it is the single most important contributor to total atmospheric nitrogen (TN) loading at this site. TN loading is enhanced several-fold over natural nitrogen loading by summertime afternoon mountain upslope flow which brings Colorado Front Range pollution nitrogen to the site. Growing season (May-October) nitrogen loading is estimated to be doubled by this pollution nitrogen deposition. The accumulation of nitrogen by this conifer forest may significantly perturb the natural forest nitrogen cycle at this site. Given that conifer foliage nitrogen content is generally < 1% of dry wt., the potential for pollution-derived nitrogen to stimulate added forest growth is high.

Keywords: deposition

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This abstract is being presented at: 2:15 PM in session:
Oral Session #28: Effects of N Deposition in Ecosystems.