Document: JON-3-59-110

Effects of atmospheric pollutants and deposition on forested ecosystems as assessed with stable isotopic composition

COMSTOCK, J.*, M.SY and R.PAUSCH

Boyce Thompson Insitute, Ithaca, NY 14853 USA ¹

Abstract:
Alterations in the integration of carbon, water, and nutrient cycling in forest stands were evaluated using stable isotopes of C, O, H, N, &S. These isotopes were measured concurrently on both soil and plant pools sampled from three national parks spanning the gradient from the Canadian to the Mexican borders of the western United States. Several patterns were apparent that reflect primarily the climatic gradient in temperature and precipitation from north to south. These are particularly clear in isotopic data of C, O, and H, which are all more negative at the more northern latitudes. Nitrogen isotopic behavior showed a more complex pattern geographically and had selected features that appear correlated with rates of pollutant deposition. The most obvious of these was a consistent age-dependence of leaf isotopic composition only in the most polluted sites. In Sequoia, the park with the highest levels of atmospheric deposition, nitrogen isotope composition shifted -0.9 per mil between 1 and three year old foliage. In addition to individual element analyses, simultaneous measurement of multiple elements permits an evaluation of changed relationships between the different cycles of water, carbon and mineral nutrition across broad gradients.

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This abstract is being presented at: 3:30 PM in session:
Poster Session #15: Nutrient Cycling.