O'Neal, Jennifer. 2000. Biological evaluation of stream enhancement: A comparison of large woody debris and an engineered alternative. M.S.
Concern for the health of aquatic systems in the Pacific Northwest has encouraged research on new methods to enhance fresh water spawning and rearing habitat (Nehlsen et al. 1991). Lack of large woody debris in streams has reduced the complexity and quality of fish habitat. This paper compared the biological performance of native large woody debris (LWD) and an organic, engineered alternative to large woody debris (ELWdTM). This study analyzed potential differences in populations of macroinvertebrates and fish associated with ELWdTM and natural LWD. Macroinvertebrate samples were from communities on the submerged surface of the wood structures and in the substrate downstream from each structure. A comparison of thirteen measures of ecological health was made to detect any significant differences between the invertebrate communities associated with each type of structure. Values of invertebrate metrics were generally higher for samples collected from ELWdTM surfaces than from traditional LWD. Benthic samples did not show a consistent difference between invertebrate communities downstream from the different types of structures. The effects of these structures on fish populations were assessed by examining spatial distribution and fish feeding behavior. Fish response was not significantly different for the two types of wood. Water velocity within habitat units was an important factor in the prediction of fish distribution. Invertebrate samples from the log surfaces and the benthic substrate were also evaluated in terms of the production of available food resources for salmonids. The results from the log surface samples showed greater food availability from the ELWdTM structures. Benthic samples did not show a clear difference between the wood types. Regression analysis revealed four significant relationships between invertebrate metrics and water quality parameters, which may deserve further study. The results of this study provide an evaluation of the effectiveness of an engineered alternative compared to traditional LWD for stream enhancement projects before engineered structures are widely placed.
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