Northwest Fisheries Science Center

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Document Type: Journal Article
Center: NWFSC
Document ID: 771
Title: Periphyton and invertebrate response to wood placement in large Pacific coastal rivers
Author: Holly J. Coe, Peter M. Kiffney, G. R. Pess, K. Kloehn, M. McHenry
Publication Year: 2009
Journal: River Research and Applications
Volume: 25
Issue: 8
Pages: 1025-1035

    Wood abundance in aquatic systems has been dramatically reduced compared to historical levels due to anthropogenic activities that led to wood removal and stream simplification.  As a result, reintroduction of wood to aquatic systems is now a widely used and relatively well–studied restoration technique for increasing habitat complexity.  Although stream periphyton (biofilm) and invertebrates serve as food sources for a variety of predators including fish, birds, and bats, data on how lower trophic levels respond to wood placement are relatively scarce.  The purpose of this study was to test the hypothesis that periphyton biomass and aquatic invertebrate density were higher on Engineered Log Jams (ELJs) than on inorganic substrates in two large Pacific Northwest river systems.  Among years and rivers, periphyton biomass and invertebrate densities were significantly higher on ELJs than on cobbles within the same reach.  Invertebrate communities on ELJs were dominated by meiofauna (<500 µm), whereas cobbles were dominated by larger chironomids.  We attribute these trophic level differences to substrate type, as we did not detect taxonomic differences between cobbles in reaches with and without ELJs.  We show that adding wood to reaches with little or no naturally occurring wood increased overall habitat surface area and thereby the potential for increased productivity relative to reaches with low levels of wood.  Finally, wood supports a unique community of invertebrates that are often overlooked in lotic system studies but may be contributing substantially to overall biological diversity.

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