1. Logjams: A Look at Logjams and Emergent Wood Effects on Insect Emergence in a Small Northern Minnesota Stream Zachary Snobl with Faculty Mentors: Todd Wellnitz and Eric Merten
Introduction
Wood performs vital functions in streams. Wood can create pools and backwater areas, trap leaves and organic matter that are food for invertebrates, and provide refuge from predators (Coe et al. 2009). Macroinvertebrate production increases upstream of wood, possibly due to organic material deposition, which many macroinvertebrates use for food (Wallace et al. 1995).
Although wood effects on benthic (i.e., bottom-dwelling) macroinvertebrates have been well-studied, surprisingly little has been published on how wood influences insect emergence.
Hypothesis
We predict that both emergent and benthic taxa richness will increase as submerged and emergent wood becomes more abundant. We also predict that wood will influence the composition of the emergent community.
Results
r2= 0.24
p= 0.04
Emergent insect taxa richness increased with emergent wood in and around a logjam in Cabin Creek. Data were collected for 3 d from 0.5-m2 emergence traps placed above wood protruding from the stream.
The NMDS shows that emerged wood surface area and submerged wood surface area are both related to changes in the community composition of emerging insects. Each point represents one emergence trap. The more a point is pulled in the direction of the arrows, the more of an effect that that variable is having on the emergent community in that trap.
Conclusion
Our results suggest that benthic and emergent taxa congregate on or around increasing amounts of stream wood.
Our data show that wood was positively related to both benthic and emergent macroinvertebrate richness and community composition. Given the importance of aquatic macroinvertebrates as a resource subsidy to adjacent riparian zones, our findings suggest that wood provides an important linkage between aquatic and terrestrial communities.
Methods
1) Randomly placed 50 floating emergence traps over a 40m stretch of stream centered on a logjam.
2) Collect benthic macroinvertebrates at each trap via Surber samples.
3) Quantified wood inside of each trap. 1 2
r2= 0.59
p< 0.001 3
Acknowledgements
I would like to thank the other student researchers that worked on this project including Jennifer Mack, Ong Xiong, John Schoen, Chris Wojan, Laura Gaffeny, Aaron DeVoe, Stephanie Vinetas, and Ashwin Sasidharan. I also would like to thank The Office of Research and Sponsored Programs and The United States Forest Service for funding this project.
Literature Citied
Coe, H.J., P.M. Kiffney, G.R. Pess, K.K. Kloehn, and M.L. McHenry Periphyton and invertebrate response to wood placement in large Pacific coastal rivers. River Research and Applications 25:
Wallace, J.B., J.R. Webster, and J.L. Meyer Influence of log additions on physical and biotic characteristics of a mountain stream. Canadian Journal of Fisheries and Aquatic Sciences 52:
Benthic macroinvertebrate taxa richness increased with submerged wood surface area in and around a logjam in Cabin Creek.