A Comparison of Methods to Evaluate the Response of Periphyton and Invertebrates to Wood Placement in Large Pacific Coastal Rivers

The goal of our study was to evaluate the importance of placed wood for periphyton and invertebrates in two large Pacific Northwest rivers systems (bankfull width>30 m) using artificial substrates, a widely used method in small streams, and natural substrates including cobble and wood. Preliminary findings suggest that artificial substrates were ineffective at mimicking invertebrate densities and community structure and periphyton biomass found on natural substrates. Artificial substrates were also logistically difficult to place and retrieve. As current methods for sampling wood are not designed for periphyton collection and are logistically difficult in large systems, we developed a new method for sampling both invertebrates and periphyton from wood in large rivers where log jams can be large and deep pool habitats are prevalent. This method proved highly effective at a) sampling invertebrates as well as finer, more easily dispersed components of periphyton and b) detecting biological responses to wood placement. Furthermore, our findings suggest that wood can be an effective instream restoration method in large river systems because it can serve as both physical refugia during high flows and as an important substrate for periphyton and invertebrates. Finally, wood supports a unique community of invertebrates that are often understudied and therefore underrepresented in lotic system studies. 1Author to whom correspondence should be addressed