Document: SAN-3-15-7

Nitrogen transfer from stream to riparian foodwebs: Results from eight ¹⁵N tracer experiments.

SANZONE, D.M.* ¹, J.L.MEYER ¹, J.L.TANK ², P.J.MULHOLLAND ³, N.B.GRIMM ⁴, S.V.GREGORY ⁵, W.H.MCDOWELL ⁶, W.B.BOWDEN ⁷ and W.K.DODDS ⁸

University of Georgia, Athens, GA, 30602 USA ¹
University of Illinois, Urbana, IL, 61801 USA ²
Oak Ridge National Lab, Oak Ridge, TN, 37831 USA ³
Arizona State University, Tempe, AZ 85287 USA ⁴
Oregon State University, Corvallis, OR 97331 USA ⁵
University of New Hampshire, Durham, NH 03824 USA ⁶
Landcare Research, Lincoln 8152, New Zealand ⁷
Kansas State University, Manhattan, KS 66506 USA ⁸

Abstract:
Movement of nutrients and organic matter between aquatic and terrestrial habitats may have a greater impact on assemblage structure and community dynamics than within-habitat inputs. In this study, we document the effect of aquatic prey subsidies on surrounding terrestrial predators in eight riparian zones using a stable isotopic ¹⁵N tracer experiment to quantify the flow of nitrogen from aquatic to terrestrial food webs via emerging aquatic insects. We continuously dripped ¹⁵N-NH₄Cl for six weeks into four temperate forested streams (North Carolina, Tennessee, New Hampshire and Oregon), one tropical forest stream (Puerto Rico), a desert stream (Arizona), a grassland stream (Kansas), and one arctic stream (Iceland), and traced the flow of ¹⁵N from the streams into spiders living in the riparian zone. After correcting for background ¹⁵N values, we used simple mixing models to calculate proportion of ¹⁵N tracer from emerging aquatic insects incorporated into spider biomass. In addition, we documented spider abundance, biomass and diversity along a transitional gradient at various distances from the stream bank (0-50m). Ground-dwelling spider abundance was highest within the first 10m of the stream bank in six of the eight streams, three of which had relatively high emergence production (desert, arctic and temperate rainforest streams). Spider ¹⁵N values were elevated above background levels and tracked that of emerging aquatic insects at these three sites, indicating a reliance on aquatic resources.

Keywords: 15N tracer, nitrogen, spiders, riparian zone, aquatic subsidies

This abstract is being presented at: 10:50 AM in session:
Symposium # 3: Linking Communities Across Ecosystem Boundaries: A Symposium in Memory of Gary A. Polis.