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McCutcheon, Kelly

Natural Resources

2005

M.S.

The importance of large woody debris (LWD) in aquatic ecosystems has been well documented. LWD serves several functions in lotic systems, providing both hydrologic stability and structural habitat complexity. This research seeks to address the latter function, as well as better understand potential LWD input sources which may be critical for managing LWD. The specific purpose of this research was twofold: first, to evaluate the relationships between LWD patches and fish and macroinvertebrate communities; and second, to understand LWD input sources and the scales at which these factors may be interacting and contributing to overall LWD loading. Most studies of stream habitat conditions collect data at a reach level, often overlooking the potential habitat heterogeneity that occurs at a more local, or patch level. We first explored relationships between large woody debris (LWD) patches and fish and macroinvertebrate communities in nine Vermont streams. In addition, we compared the effectiveness of biotic sampling strategies at the reach and patch level. Habitat measures, as well as fish and macroinvertebrate samples were taken at both the reach and patch level. At each study site, we evaluated the potential LWD habitat available and characterized these patches based on physical and biological parameters such periphyton, length, width, embeddedness, and position relative to flow. Paired t-test results suggest that LWD is providing important patch habitat for fish and macroinvertebrates. Fish densities and percent Chironomidae were both higher at LWD patches than at reach subsamples. Spearman rank correlations indicate that fish and macroinvertebrates use patches in different ways; while fish preferred larger pieces of LWD, macroinvertebrates were found in higher abundance around more moderately sized pieces. We concluded that sampling at a reach level may not accurately portray the community composition of a stream environment because the unique biodiversity in patches such as LWD may be overlooked. This research illustrates the need to restore and maintain patchiness in order to promote biodiversity and stream health.
With this knowledge, we sought to better understand LWD sources, variables controlling LWD distribution, and the scale at which these factors interact. This understanding is critical to manage surrounding terrestrial systems for the production and input of LWD. Our second objective was to explore the interactions of watershed and local scale land use and their effects on LWD input to Vermont streams. More specifically, we evaluated the relative importance of land cover characteristics at the watershed, watershed riparian (100 m buffer of entire stream), and local riparian (50 m buffer of stream reach) scales, as well as local geomorphic conditions as potential contributors to LWD recruitment and distribution in nine study reaches. We used the information theoretic method to model relationships between LWD response variables and key LWD input and distribution variables. Our models with the greatest support suggest that LWD recruitment and distribution relates to various local and regional landscape attributes. The results suggest that management of the riparian zone is important to maintaining adequate LWD loading, however, larger scale factors may also influence LWD recruitment. Understanding the input of LWD into streams requires looking across scales at a combination of sources and land use factors.