Author: Scott Jungblom

Publisher:

Published: 2002

Total Pages: 202

ISBN-13:

"Past stream habitat restoration has been focused primarily on increasing specific fish populations with little knowledge of how these habitat manipulations affect the benthic macroinvertebrate community. This study focuses on assessing the immediate effects of instream habitat restoration structures on the benthic macroinvertebrate community and its environment. Physical measurements, water quality measurements, benthic invertebrate and substrate composition samples were taken at three experimental structure locations and one upstream control site twice before structure placement in June and July 1998 and twice after structure placement (October and November 1998). Six benthic samples were taken at each site on each sample date. Three samples each were taken five meters above and below the structure site, sampling a ten-meter zone of impact for each structure. The Kalispel Natural Resource Department built a series of salmonid stream habitat restoration structures in Cee Cee Ah Creek of Pend Oreille Co. Washington in August of 1998. Experimental site 1 received a modified single log weir or channel constrictor, site 2 received a K-dam and site 3 received an upstream-V weir. Comparisons were made between data collected at each site before structure placement vs. after and between each experimental site vs. the upstream control site. All sites shared similar physical and water quality data within each sample date except for slight differences in stream width, embeddedness, and discharge, which changed seasonally. Cobble dominated the system with a high percentage of gravel substrate present at site 3. Structure construction resulted in an increase in stream width and depth at each site above and/or below each structure. There was no significant difference in benthic density or community metric analysis between upstream and downstream samples at any site throughout the study. Therefor upstream and downstream samples were combined to assess each structure's complete ten-meter zone of impact. The upstream control site density did not change significantly throughout the study. However, the density of each experimental site (site 1, site 2, and site 3) and the combined experimental sites (site 1+2+3) did increase significantly in post structure samples (October and November combined). There was no significant difference in the density of the control site and experimental sites one or three either before or after structure placement. However, the density at site 2 (K-Dam) and at the combined experimental sites was significantly higher than the control site after structure placement (October and November combined). Community composition did not change significantly throughout the study at any site and there was no difference between the control site and any experimental site before or after structure placement. The total number of families present during the study was 60, dominated by Chironomidae at site 1 and alternated between Chironomidae and Heptageniidae at the control site, and experimental sites 2 and 3. While the number of feeding guild taxa did not change significantly at any site during the study, the percent shredder composition increased at all three structure sites for both post-structure sample dates. The upstream control did not show a similar trend. Analysis of each sample's volumetric substrate composition in relation to its invertebrate metrics values showed significant differences in metric values corresponding to certain substrate compositions for all the metrics tested except Percent Dominant Family. Samples with reduced small, medium, large and combined gravel compositions and increased cobble + boulder concentration showed an increase in water quality for the metrics: Density, Total Number of Taxa, EPT Index, and the Shannon-Weiner diversity index. However samples with the above substrate compositions showed a decrease in water quality for the metrics: Scraper/Collector ratio, percent EPT, EPT/C ratio and FBI score. This study shows that instream habitat restoration structures significantly increased local macroinvertebrate density and did not jeopardize community diversity or composition. By using instream structures that create specific substrate class compositions habitat managers may be able to enhance problem macroinvertebrate community metrics found in initial assessments. While the scope of this study was restricted to short-term effects on a specific habitat, these results clearly identified the benefits of instream structures as well as the need for future long-term studies to include pre-restoration sampling at control or reference sites"--Document.