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Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, 2002
in Food Webs
ROLE OF RIPARIAN RED ALDER IN SHAPING HEADWATER STREAM NUTRIENT DYNAMICS AND AQUATIC COMMUNITIES.
C.J. Volk1, P.M. Kiffney2, and R.L. Edmonds1. 1Center for Streamside Studies, College of Forest Resources, University of Washington, Seattle, Washington, U.S.A., 2National Marine Fisheries Service, Northwest Fisheries Science Center, Seattle, Washington, U.S.A.
Riparian vegetation provides an important subsidy of organic matter and nutrients to aquatic ecosystems. In the Pacific Northwest, natural disturbance events (e.g., fire) and clearcutting have contributed to the predominance of red alder (Alnus rubra) in riparian corridors. Current management supports the removal of nitrogen-fixing red alder and replacement with conifers because they provide a more stable supply of large woody debris to streams, and thus form important fish habitat. However, our previous research has shown water, seston, leaf litter, and periphyton from red alder-dominated streams to have higher biomass and macronutrient concentrations; these food resources may provide critical sources of nutrients for fish and amphibians. To compare the structure and resource derivation of red alder and conifer food webs, we collected vegetation, periphyton, invertebrates, and amphibians for 13C and 15N stable isotope analyses from four streams: two dominated by red alder and two by old-growth conifers. Preliminary analyses have shown vegetation and invertebrate shredders from alder sites to have higher δ15N content than conifer-dominated sites. In addition, the δ13C signature of invertebrates (grazer, filter feeder, predator, and aggregate benthic samples) from alder streams was higher compared to conifer-dominated systems, suggesting differences in invertebrate food source derivation between stream systems.
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