Document: JAC-3-15-8

Use and limits of natural abundance stable isotope measurements to understand watershed-river exchange.

FINLAY, J.* ¹, G.CABANA ², W.RAINEY ¹, M.POWER ¹, J.L.BASTOW ¹ and A.P.SMYTH ¹

University of California, Berkeley, Berkeley, CA 94720-3140 USA ¹
Universite du Quebec a Trois-Rivieres, Trois-Rivieres, Quebec, Canada ²

Abstract:
Natural abundance stable isotope measurements are increasingly used to identify previously unknown or unquantified trophic connections between terrestrial and aquatic ecosystems. Here we examine the controls of stable carbon (C) and nitrogen (N) isotope ratios of riparian and river primary producers to assess the contribution of terrestrial and aquatic ecosystems to river and near-river food webs. Algal ¹³C are broadly controlled by the balance of heterotrophic and autotrophic processes in streams. As forest canopy cover decreases with increasing stream size, stable carbon isotope measurements show that contributions of algal carbon to stream food webs increase sharply. Preliminary data suggest that transfer of algal carbon to riparian food webs follows a similar pattern, although overlap between terrestrial and algal ¹³C is more common in productive rivers. Algal ¹⁵N are influenced by sources and cycling of N in streams. Differences between terrestrial and algal ¹⁵N may allow distinction of organic matter sources to river and riparian food webs. Thus, under some circumstances, the response of stable isotope ratios in food webs to variation in watershed biogeochemistry will provide tracers to determine the sources or scales of watershed-river exchange.

Keywords:

This abstract is being presented at: 8:50 AM in session:
Symposium # 3: Linking Communities Across Ecosystem Boundaries: A Symposium in Memory of Gary A. Polis.