Document: SHE-3-15-2

Terrestrial-aquatic linkages in a Pacific Northwest old-growth forest: Results from an aquatic ¹⁵N tracer study.

JOHNSON, S.L.*, L.R.ASHKENAS and S.V.GREGORY

Oregon State University, Corvallis, OR 97331 USA ¹

Abstract:
Many studies in lotic ecology have focused on the influences of riparian forests on stream structure and function. However, few have examined stream influences on riparian forests and terrestrial vertebrates. We added ¹⁵N -NH₄ for 6 weeks to Mack Creek, a third-order stream in the H.J. Andrews Experimental Forest, Oregon. At the end of this release, we sampled leaves, roots and stems of 4 perennial riparian species from four sites along a 200 m longitudinal gradient. We observed significant enrichment of all 4 species. However, the pattern of enrichment varied substantially among species: leaves, stems and roots of oxalis (Oxalis oregana) had similar levels of enrichment (¹⁵N ~28^o/_oo), while the leaves of lady fern (Athyrium filix-femina ) were only slighlty enriched (¹⁵N=2^o/_oo) compared to their roots (¹⁵N=53^o/_oo). Leaves from an additional 15 species, sampled at one site, exhibited similar variation. Our results suggest that these riparian species have high hydraulic connectivity with stream water, but differ in their partitioning of N. A stream-foraging bird, the dipper (Cinclus mexicanus), and 3 species of small riparian mammals also showed slight ¹⁵N enrichment. Stream N budgets usually do not account for terrestrial uptake of N but our calculations suggest that it may in fact be important.

Keywords: riparian, nitrogen, stream, LINX

This abstract is being presented at: 8:30 AM in session:
Symposium # 3: Linking Communities Across Ecosystem Boundaries: A Symposium in Memory of Gary A. Polis.